5709 lines
228 KiB
Plaintext
5709 lines
228 KiB
Plaintext
From owner-pgsql-hackers@hub.org Tue Oct 13 15:05:53 1998
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Received: from hub.org (majordom@hub.org [209.47.148.200])
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for <hackers@postgreSQL.org>; Tue, 13 Oct 1998 14:53:22 -0400
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Date: Tue, 13 Oct 1998 14:53:22 -0400 (EDT)
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From: Terry Mackintosh <terry@terrym.com>
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X-Sender: terry@terry1.acun.com
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Reply-To: Terry Mackintosh <terry@terrym.com>
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To: PostgreSQL-development <hackers@postgreSQL.org>
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Subject: Re: [HACKERS] What about LIMIT in SELECT ?
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In-Reply-To: <Pine.GSO.3.96.SK.981013211058.17758A-100000@ra>
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Message-ID: <Pine.LNX.3.95.981013141634.9255C-100000@terry1.acun.com>
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Sender: owner-pgsql-hackers@postgreSQL.org
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Precedence: bulk
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Status: ROr
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Hi, my 2 cents...
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I agree completely, LIMIT would be VERY usefull in web based apps, which
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is all I run. It does not matter to me if it is not part of a formal
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standard. The idea is so common that it is a defacto standard.
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I would not expect it for this release, but could it get put on the TODO
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list for next time? I am even willing to work at an apprentise level on
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this with a more expeireanced person that knows this stuff.
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A note on implimentation:
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I *used to* :) work with VFP on NT's :(
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And the way VFP did LIMIT, it would only return the number of rows asked
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for, BUT it still did the WHOLE search!
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So on a larger table, which we had (property tax database for the county),
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if some one put in too vague a query, it would try to collect ALL of the
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rows as the initial result set, then give you the first x rows of that.
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This did save on pushing mass amounts of data out to the browser, but it
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would have been even better if it could have simply aborted the select
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after having found x rows.
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Also, it did not have the concept of an offset, so one could not select
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100 rows, starting 200 rows in, which would be REALLY usefull for "paging"
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through data. I do not know if mySQL or any other has such a concept
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either, but it would be nice.
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So a properly implemented "LIMIT" could:
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1. Save pushing mass amounts of data across the web, that no one wants
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any way.
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2. Stop vague queries from bogging down the server.
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(On very larg tables this could be critical!)
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3. Enable "Paging" of data. (easyer then now (app. level))
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4. Would be a very nice feather in PostgreSQL's cap that could make it
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even more attractive to those looking at all sorts of databases out there.
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Have a great day.
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On Tue, 13 Oct 1998, Oleg Bartunov wrote:
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> Hi,
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>
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> I took a look at mysql and was very impressed with possibility
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> to limit number of rows returned from select. This is very useful
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> feature for Web applications when user need to browse results of
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> selection page by page. In my application I have to do full
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> select every time user press button [Next] and show requested page
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> using perl. This works more or less ok for several thousands rows but
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> totally unusable for large selections. But now I'm about to work
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> with big database and I don't know how I'll stay with postgres :-)
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> It'll just doesn't work if customer will wait several minutes just browse
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> next page. Mysql lacks some useful features postgres has
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> (subselects, transaction ..) but for most Web applications I need
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> just select :-) I dont' know how LIMIT is implemented in Mysql and
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> I know it's not in SQL92 standart, but this makes Mysql very popular.
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>
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> Is it difficult to implement this feature in postgres ?
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>
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> Regards,
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>
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> Oleg
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>
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>
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> _____________________________________________________________
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> Oleg Bartunov, sci.researcher, hostmaster of AstroNet,
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> Sternberg Astronomical Institute, Moscow University (Russia)
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> Internet: oleg@sai.msu.su, http://www.sai.msu.su/~megera/
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> phone: +007(095)939-16-83, +007(095)939-23-83
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>
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>
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Terry Mackintosh <terry@terrym.com> http://www.terrym.com
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sysadmin/owner Please! No MIME encoded or HTML mail, unless needed.
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Proudly powered by R H Linux 4.2, Apache 1.3, PHP 3, PostgreSQL 6.3
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-------------------------------------------------------------------
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Success Is A Choice ... book by Rick Patino, get it, read it!
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From owner-pgsql-hackers@hub.org Tue Oct 13 18:12:41 1998
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for <hackers@postgreSQL.org>; Tue, 13 Oct 1998 17:54:36 -0400 (EDT)
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Tue, 13 Oct 1998 16:55:35 -0500 (CDT)
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Message-ID: <006701bdf6f4$60ed75f0$c525c4ce@go-to-jail.remapcorp.com>
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From: "Jeff Hoffmann" <jeff@remapcorp.com>
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To: "Marc G. Fournier" <scrappy@hub.org>, "Eric Lee Green" <eric@linux-hw.com>
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Cc: "PostgreSQL-development" <hackers@postgreSQL.org>
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Subject: Re: [HACKERS] What about LIMIT in SELECT ?
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Date: Tue, 13 Oct 1998 16:56:48 -0500
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Sender: owner-pgsql-hackers@postgreSQL.org
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Status: RO
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>On Tue, 13 Oct 1998, Eric Lee Green wrote:
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>
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>> On Tue, 13 Oct 1998, Jeff Hoffmann wrote:
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>> > >I agree completely, LIMIT would be VERY usefull in web based apps,
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which
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>> > >is all I run. It does not matter to me if it is not part of a formal
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>> > >standard. The idea is so common that it is a defacto standard.
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>> >
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>> > i'm not familiar with mysql and using "LIMIT" but wouldn't this same
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effect
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>> > be achieved by declaring a cursor and fetching however many records in
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the
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>> > cursor? it's a very noticeable improvement when you only want the
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first 20
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>> > out of 500 in a 200k record database, at least.
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>>
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>> The problem with declaring a cursor vs. the "LIMIT" clause is that the
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>> "LIMIT" clause, if used properly by the database engine (along with the
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>> database engine using indexes in "ORDER BY" clauses) allows the database
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>> engine to short-circuit the tail end of the query. That is, if you have
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25
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>> names and the last one ends with BEAVIS, the database engine doesn't have
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>> to go through the BUTTHEADS and KENNYs and etc.
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>>
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>> Theoretically a cursor is superior to the "LIMIT" clause because you're
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>> eventually going to want the B's and K's and etc. anyhow -- but only in a
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>> stateful enviornment. In the stateless web environment, a cursor is
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>> useless because the connection can close at any time even when you're
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>> using "persistent" connections (and of course when the connection closes
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>> the cursor closes).
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>
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>Ookay, I'm sorry, butyou lost me here. I haven't gotten into using
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>CURSORs/FETCHs yet, since I haven't need it...but can you give an example
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>of what you would want to do using a LIMIT? I may be missing something,
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>but wha is the different between using LIMIT to get X records, and
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>definiing a cursor to FETCH X records?
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>
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>Practical example of *at least* the LIMIT side would be good, so that we
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>can at least see a physical example of what LIMIT can do that
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>CURSORs/FETCH can't...
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>
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fetch with cursors should work properly (i.e., you can short circuit it by
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just ending your transaction) my understanding on how this works is exactly
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how you explained LIMIT to work. here's some empirical proof from one of my
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sample databases:
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the sample table i'm using has 156k records (names of people)
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i'm using a PP180 with 128MB RAM and some old slow SCSI drives.
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public_mn=> select count(*) from public_ramsey;
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count
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------
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156566
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(1 row)
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i did the following query:
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public_mn=> select * from public_ramsey where ownerlname ~ 'SMITH';
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which returned 711 matches and took about 12 seconds.
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i did the same thing with a cursor:
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public_mn=> begin;
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BEGIN
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public_mn=> declare test cursor for select * from public_ramsey where
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ownerlname ~ 'SMITH';
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SELECT
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the select was instantaneous.
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public_mn=> fetch 20 in test;
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returns 20 records almost instantaneously. each additional 20 took less
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than a second, as well.
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if this isn't what you're talking about, i don't understand what you're
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saying.
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jeff
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From eric@ireland.linux-hw.com Tue Oct 13 18:52:42 1998
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Received: from ireland.linux-hw.com (IDENT:eric@ireland.linux-hw.com [199.72.95.215])
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Tue, 13 Oct 1998 18:55:22 -0400
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Date: Tue, 13 Oct 1998 18:55:22 -0400 (EDT)
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From: Eric Lee Green <eric@linux-hw.com>
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To: Bruce Momjian <maillist@candle.pha.pa.us>
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cc: jeff@remapcorp.com, hackers@postgreSQL.org
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Subject: Re: [HACKERS] What about LIMIT in SELECT ?
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In-Reply-To: <199810132116.RAA11249@candle.pha.pa.us>
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Message-ID: <Pine.LNX.3.96.981013184022.31202B-100000@ireland.linux-hw.com>
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MIME-Version: 1.0
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Content-Type: TEXT/PLAIN; charset=US-ASCII
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Status: RO
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On Tue, 13 Oct 1998, Bruce Momjian wrote:
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> > Theoretically a cursor is superior to the "LIMIT" clause because you're
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> > eventually going to want the B's and K's and etc. anyhow -- but only in a
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> > stateful enviornment. In the stateless web environment, a cursor is
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> > useless because the connection can close at any time even when you're
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> > using "persistent" connections (and of course when the connection closes
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> What we could do is _if_ there is only one table(no joins), and an index
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> exists that matches the ORDER BY, we could use the index to
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> short-circuit the query.
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This is exactly what MySQL does in this situation, except that it can use
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the ORDER BY to do the short circuiting even if there is a join involved
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if all of the elements of the ORDER BY belong to one table. Obviously if
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I'm doing an "ORDER BY table1.foo table2.bar" that isn't going to work!
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But "select table1.fsname,table1.lname,table2.receivables where
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table2.receivables > 0 and table1.custnum=table2.custnum order by
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(table1.lname,table1.fsname) limit 50" can be short-circuited by fiddling
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with the join order -- table1.fsname table1.lname have to be the first two
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things in the join order.
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Whether this is feasible in PostgreSQL I have no earthly idea. This would
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seem to conflict with the join optimizer.
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> happier? If there is an ORDER BY and no index, or a join, I can't
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> figure out how we would short-circuit the query.
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If there is an ORDER BY and no index you can't short-circuit the query.
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MySQL doesn't either. Under certain circumstances (such as above) you can
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short-circuit a join, but it's unclear whether it'd be easy to add such
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a capability to PostgreSQL given the current structure of the query
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optimizer. (And I certainly am not in a position to tackle it, at the
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moment MySQL is sufficing for my project despite the fact that it is
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quite limited compared to PostgreSQL, I need to get my project finished
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first).
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--
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Eric Lee Green eric@linux-hw.com http://www.linux-hw.com/~eric
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"To call Microsoft an innovator is like calling the Pope Jewish ..."
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-- James Love (Consumer Project on Technology)
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From owner-pgsql-hackers@hub.org Wed Oct 14 09:01:01 1998
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From: jwieck@debis.com (Jan Wieck)
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Subject: Re: [HACKERS] What about LIMIT in SELECT ?
|
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To: eric@linux-hw.com (Eric Lee Green)
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Date: Wed, 14 Oct 1998 13:09:21 +0200 (MET DST)
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Cc: jeff@remapcorp.com, hackers@postgreSQL.org
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Reply-To: jwieck@debis.com (Jan Wieck)
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In-Reply-To: <Pine.LNX.3.96.981013161955.30555A-100000@ireland.linux-hw.com> from "Eric Lee Green" at Oct 13, 98 04:24:20 pm
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Status: ROr
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|
Eric Lee Green wrote:
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>
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|
> On Tue, 13 Oct 1998, Jeff Hoffmann wrote:
|
|
> > >I agree completely, LIMIT would be VERY usefull in web based apps, which
|
|
> > >is all I run. It does not matter to me if it is not part of a formal
|
|
> > >standard. The idea is so common that it is a defacto standard.
|
|
> >
|
|
> > i'm not familiar with mysql and using "LIMIT" but wouldn't this same effect
|
|
> > be achieved by declaring a cursor and fetching however many records in the
|
|
> > cursor? it's a very noticeable improvement when you only want the first 20
|
|
> > out of 500 in a 200k record database, at least.
|
|
>
|
|
> The problem with declaring a cursor vs. the "LIMIT" clause is that the
|
|
> "LIMIT" clause, if used properly by the database engine (along with the
|
|
> database engine using indexes in "ORDER BY" clauses) allows the database
|
|
> engine to short-circuit the tail end of the query. That is, if you have 25
|
|
> names and the last one ends with BEAVIS, the database engine doesn't have
|
|
> to go through the BUTTHEADS and KENNYs and etc.
|
|
>
|
|
> Theoretically a cursor is superior to the "LIMIT" clause because you're
|
|
> eventually going to want the B's and K's and etc. anyhow -- but only in a
|
|
> stateful enviornment. In the stateless web environment, a cursor is
|
|
> useless because the connection can close at any time even when you're
|
|
> using "persistent" connections (and of course when the connection closes
|
|
> the cursor closes).
|
|
|
|
I'm missing something. Well it's right that in the stateless
|
|
web environment a cursor has to be declared and closed for
|
|
any single CGI call. But even if you have a LIMIT clause,
|
|
your CGI must know with which key to start.
|
|
|
|
So your query must look like
|
|
|
|
SELECT ... WHERE key > 'last processed key' ORDER BY key;
|
|
|
|
And your key must be unique (or at least contain no duplicate
|
|
entries) or you might miss some rows between the pages (have
|
|
100 Brown's in the table and last processed key was a Brown
|
|
while using LIMIT).
|
|
|
|
In postgres you could actually do the following (but read on
|
|
below - it's not optimized correct)
|
|
|
|
BEGIN;
|
|
DECLARE c CURSOR FOR SELECT ... WHERE key > 'last' ORDER BY key;
|
|
FETCH 20 IN c;
|
|
(process the 20 rows in CGI)
|
|
CLOSE c;
|
|
COMMIT;
|
|
|
|
Having LIMIT looks more elegant and has less overhead in CGI-
|
|
backend communication. But the cursor version is SQL
|
|
standard and portable.
|
|
|
|
>
|
|
> I wanted very badly to use PostgreSQL for a web project I'm working on,
|
|
> but it just wouldn't do the job :-(.
|
|
|
|
I've done some tests and what I found out might be a bug in
|
|
PostgreSQL's query optimizer. Having a table with 25k rows
|
|
where key is a text field with a unique index. Now I used
|
|
EXPLAIN for some queries
|
|
|
|
SELECT * FROM tab;
|
|
|
|
results in a seqscan - expected.
|
|
|
|
SELECT * FROM tab ORDER BY key;
|
|
|
|
results in a sort->seqscan - I would have
|
|
expected an indexscan!
|
|
|
|
SELECT * FROM tab WHERE key > 'G';
|
|
|
|
results in an indexscan - expected.
|
|
|
|
SELECT * FROM tab WHERE key > 'G' ORDER BY key;
|
|
|
|
results in a sort->indexscan - hmmm.
|
|
|
|
These results stay the same even if I blow up the table by
|
|
duplicating all rows (now with a non-unique index) to 100k
|
|
rows and have them presorted in the table.
|
|
|
|
Needless to say that everything is vacuum'd for statistics.
|
|
|
|
The last one is the query we would need in the web
|
|
environment used over a cursor as in the example above. But
|
|
due to the sort, the backend selects until the end of the
|
|
table, sorts them and then returns only the first 20 rows
|
|
(out of sorts result).
|
|
|
|
This is very painful if the qualification (key > ...) points
|
|
to the beginning of the key list.
|
|
|
|
Looking at planner.c I can see, that if there is a sortClause
|
|
in the parsetree, the planner creates a sort node and does
|
|
absolutely not check if there is an index that could be used
|
|
to do it. In the examples above, the sort is absolutely
|
|
needless because the index scan will already return the
|
|
tuples in the right order :-).
|
|
|
|
Somewhere deep in my brain I found a statement that sorting
|
|
sorted data isn't only unnecessary (except the order
|
|
changes), it is slow too compared against sorting randomly
|
|
ordered data.
|
|
|
|
Can we fix this before 6.4 release, will it be a past 6.4 or
|
|
am I doing something wrong here? I think it isn't a fix (it's
|
|
a planner enhancement) so it should really be a past 6.4
|
|
item.
|
|
|
|
For now, the only possibility is to omit the ORDER BY in the
|
|
query and hope the planner will always generate an index scan
|
|
(because of the qualification 'key > ...'). Doing so I
|
|
selected multiple times 20 rows (with the last key qual like
|
|
a CGI would do) in separate transactions. Using cursor and
|
|
fetch speeds up the access by a factor of 1000! But it is
|
|
unsafe and thus NOT RECOMMENDED! It's only a test if cursors
|
|
can do the LIMIT job - and they could if the planner would do
|
|
a better job.
|
|
|
|
|
|
Jan
|
|
|
|
--
|
|
|
|
#======================================================================#
|
|
# It's easier to get forgiveness for being wrong than for being right. #
|
|
# Let's break this rule - forgive me. #
|
|
#======================================== jwieck@debis.com (Jan Wieck) #
|
|
|
|
|
|
|
|
|
|
From owner-pgsql-hackers@hub.org Wed Oct 14 11:02:04 1998
|
|
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|
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|
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|
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|
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|
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|
|
Wed, 14 Oct 1998 15:53:53 +0300 (MSK)
|
|
Date: Wed, 14 Oct 1998 16:53:53 +0400 (MSD)
|
|
From: Oleg Bartunov <oleg@sai.msu.su>
|
|
X-Sender: megera@ra
|
|
Reply-To: Oleg Bartunov <oleg@sai.msu.su>
|
|
To: hackers@postgreSQL.org
|
|
cc: t-ishii@sra.co.jp
|
|
Subject: Re: [HACKERS] What about LIMIT in SELECT ?
|
|
In-Reply-To: <m0zTOnx-000EBRC@orion.SAPserv.Hamburg.dsh.de>
|
|
Message-ID: <Pine.GSO.3.96.SK.981014163020.10948B-100000@ra>
|
|
Organization: Sternberg Astronomical Institute (Moscow University)
|
|
MIME-Version: 1.0
|
|
Content-Type: TEXT/PLAIN; charset=US-ASCII
|
|
Sender: owner-pgsql-hackers@postgreSQL.org
|
|
Precedence: bulk
|
|
Status: RO
|
|
|
|
On Wed, 14 Oct 1998, Jan Wieck wrote:
|
|
|
|
> Date: Wed, 14 Oct 1998 13:09:21 +0200 (MET DST)
|
|
> From: Jan Wieck <jwieck@debis.com>
|
|
> To: Eric Lee Green <eric@linux-hw.com>
|
|
> Cc: jeff@remapcorp.com, hackers@postgreSQL.org
|
|
> Subject: Re: [HACKERS] What about LIMIT in SELECT ?
|
|
>
|
|
> Eric Lee Green wrote:
|
|
> >
|
|
> > On Tue, 13 Oct 1998, Jeff Hoffmann wrote:
|
|
> > > >I agree completely, LIMIT would be VERY usefull in web based apps, which
|
|
> > > >is all I run. It does not matter to me if it is not part of a formal
|
|
> > > >standard. The idea is so common that it is a defacto standard.
|
|
> > >
|
|
> > > i'm not familiar with mysql and using "LIMIT" but wouldn't this same effect
|
|
> > > be achieved by declaring a cursor and fetching however many records in the
|
|
> > > cursor? it's a very noticeable improvement when you only want the first 20
|
|
> > > out of 500 in a 200k record database, at least.
|
|
> >
|
|
> > The problem with declaring a cursor vs. the "LIMIT" clause is that the
|
|
> > "LIMIT" clause, if used properly by the database engine (along with the
|
|
> > database engine using indexes in "ORDER BY" clauses) allows the database
|
|
> > engine to short-circuit the tail end of the query. That is, if you have 25
|
|
> > names and the last one ends with BEAVIS, the database engine doesn't have
|
|
> > to go through the BUTTHEADS and KENNYs and etc.
|
|
> >
|
|
> > Theoretically a cursor is superior to the "LIMIT" clause because you're
|
|
> > eventually going to want the B's and K's and etc. anyhow -- but only in a
|
|
> > stateful enviornment. In the stateless web environment, a cursor is
|
|
> > useless because the connection can close at any time even when you're
|
|
> > using "persistent" connections (and of course when the connection closes
|
|
> > the cursor closes).
|
|
>
|
|
> I'm missing something. Well it's right that in the stateless
|
|
> web environment a cursor has to be declared and closed for
|
|
> any single CGI call. But even if you have a LIMIT clause,
|
|
> your CGI must know with which key to start.
|
|
>
|
|
This is not a problem for CGI-script to know which key to start.
|
|
Without LIMIT every CGI call backend will do *FULL* selection
|
|
and cursor helps just in fetching a definite number of rows,
|
|
in principle I can do this with CGI-script. Also, cursor
|
|
returns data back in ASCII format (man l declare) and this requires
|
|
additional job for backend to convert data from intrinsic (binary)
|
|
format. Right implementation of LIMIT offset,number_of_rows could be
|
|
a great win and make postgres superior free database engine for
|
|
Web applications. Many colleagues of mine used mysql instead of
|
|
postgres just because of lacking LIMIT. Tatsuo posted a patch
|
|
for set query_limit to 'num', I just tested it and seems it
|
|
works fine. Now, we need only possibility to specify offset,
|
|
say
|
|
set query_limit to 'offset,num'
|
|
( Tatsuo, How difficult to do this ?)
|
|
and LIMIT problem will ne gone.
|
|
|
|
I'm wonder how many useful patches could be hidden from people :-),
|
|
|
|
Regards,
|
|
|
|
Oleg
|
|
|
|
PS.
|
|
|
|
Tatsuo, do you have patch for 6.3.2 ?
|
|
I can't wait for 6.4 :-)
|
|
_____________________________________________________________
|
|
Oleg Bartunov, sci.researcher, hostmaster of AstroNet,
|
|
Sternberg Astronomical Institute, Moscow University (Russia)
|
|
Internet: oleg@sai.msu.su, http://www.sai.msu.su/~megera/
|
|
phone: +007(095)939-16-83, +007(095)939-23-83
|
|
|
|
|
|
|
|
|
|
|
|
From owner-pgsql-hackers@hub.org Wed Oct 14 11:02:00 1998
|
|
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|
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Wed, 14 Oct 1998 13:59:56 GMT
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Message-ID: <3624AE5C.752E4E7F@alumni.caltech.edu>
|
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Date: Wed, 14 Oct 1998 13:59:56 +0000
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From: "Thomas G. Lockhart" <lockhart@alumni.caltech.edu>
|
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|
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MIME-Version: 1.0
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To: Jan Wieck <jwieck@debis.com>
|
|
CC: Eric Lee Green <eric@linux-hw.com>, jeff@remapcorp.com,
|
|
hackers@postgreSQL.org
|
|
Subject: Re: [HACKERS] What about LIMIT in SELECT ?
|
|
References: <m0zTOnx-000EBRC@orion.SAPserv.Hamburg.dsh.de>
|
|
Content-Type: text/plain; charset=us-ascii
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Content-Transfer-Encoding: 7bit
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Sender: owner-pgsql-hackers@postgreSQL.org
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Precedence: bulk
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Status: ROr
|
|
|
|
> I've done some tests and what I found out might be a bug in
|
|
> PostgreSQL's query optimizer.
|
|
> SELECT * FROM tab ORDER BY key;
|
|
> results in a sort->seqscan - I would have
|
|
> expected an indexscan!
|
|
|
|
Given that a table _could_ be completely unsorted on disk, it is
|
|
probably reasonable to suck the data in for a possible in-memory sort
|
|
rather than skipping around the disk to pick up individual tuples via
|
|
the index. Don't know if vacuum has a statistic on "orderness"...
|
|
|
|
> SELECT * FROM tab WHERE key > 'G' ORDER BY key;
|
|
> results in a sort->indexscan - hmmm.
|
|
> The last one is the query we would need in the web
|
|
> environment used over a cursor as in the example above. But
|
|
> due to the sort, the backend selects until the end of the
|
|
> table, sorts them and then returns only the first 20 rows
|
|
> (out of sorts result).
|
|
|
|
So you are saying that for this last case the sort was unnecessary? Does
|
|
the backend traverse the index in the correct order to guarantee that
|
|
the tuples are coming out already sorted? Does a hash index give the
|
|
same plan (I would expect a sort->seqscan for a hash index)?
|
|
|
|
- Tom
|
|
|
|
|
|
From owner-pgsql-hackers@hub.org Wed Oct 14 11:01:52 1998
|
|
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|
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From: jwieck@debis.com (Jan Wieck)
|
|
Subject: Re: [HACKERS] What about LIMIT in SELECT ?
|
|
To: oleg@sai.msu.su
|
|
Date: Wed, 14 Oct 1998 16:24:56 +0200 (MET DST)
|
|
Cc: hackers@postgreSQL.org, t-ishii@sra.co.jp
|
|
Reply-To: jwieck@debis.com (Jan Wieck)
|
|
In-Reply-To: <Pine.GSO.3.96.SK.981014163020.10948B-100000@ra> from "Oleg Bartunov" at Oct 14, 98 04:53:53 pm
|
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X-Mailer: ELM [version 2.4 PL25]
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|
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Status: RO
|
|
|
|
Oleg Bartunov wrote:
|
|
> This is not a problem for CGI-script to know which key to start.
|
|
|
|
Never meant that would be a problem. A FORM variable will of
|
|
course do this.
|
|
|
|
> Without LIMIT every CGI call backend will do *FULL* selection
|
|
> and cursor helps just in fetching a definite number of rows,
|
|
> in principle I can do this with CGI-script. Also, cursor
|
|
> returns data back in ASCII format (man l declare) and this requires
|
|
> additional job for backend to convert data from intrinsic (binary)
|
|
> format. Right implementation of LIMIT offset,number_of_rows could be
|
|
> a great win and make postgres superior free database engine for
|
|
> Web applications. Many colleagues of mine used mysql instead of
|
|
|
|
That's the point I was missing. The offset!
|
|
|
|
> postgres just because of lacking LIMIT. Tatsuo posted a patch
|
|
> for set query_limit to 'num', I just tested it and seems it
|
|
> works fine. Now, we need only possibility to specify offset,
|
|
> say
|
|
> set query_limit to 'offset,num'
|
|
> ( Tatsuo, How difficult to do this ?)
|
|
> and LIMIT problem will ne gone.
|
|
|
|
Think you haven't read my posting completely. Even with the
|
|
executor limit, the complete scan into the sort is done by
|
|
the backend. You need to specify ORDER BY to get the same
|
|
list again (without the offset doesn't make sense). But
|
|
currently, ORDER BY forces a sort node into the query plan.
|
|
|
|
What the executor limit tells is how many rows will be
|
|
returned from the sorted data. Not what goes into the sort.
|
|
Filling the sort and sorting the data consumes the most time
|
|
of the queries execution.
|
|
|
|
I haven't looked at Tatsuo's patch very well. But if it
|
|
limits the amount of data going into the sort (on ORDER BY),
|
|
it will break it! The requested ordering could be different
|
|
from what the choosen index might return. The used index is
|
|
choosen by the planner upon the qualifications given, not the
|
|
ordering wanted.
|
|
|
|
So if you select WHERE b = 1 ORDER BY a, then it will use an
|
|
index on attribute b to match the qualification. The complete
|
|
result of that index scan goes into the sort to get ordered
|
|
by a. If now the executor limit stops sort filling after the
|
|
limit is exceeded, only the same tuples will go into the sort
|
|
every time. But they have nothing to do with the requested
|
|
order by a.
|
|
|
|
What LIMIT first needs is a planner enhancement. In file
|
|
backend/optimizer/plan/planner.c line 284 it must be checked
|
|
if the actual plan is an indexscan, if the indexed attributes
|
|
are all the same as those in the given sort clause and that
|
|
the requested sort order (operator) is that what the index
|
|
will return. If that all matches, it can ignore the sort
|
|
clause and return the index scan itself.
|
|
|
|
Second enhancement must be the handling of the offset. In
|
|
the executor, the index scan must skip offset index tuples
|
|
before returning the first. But NOT if the plan isn't a
|
|
1-table-index-scan. In that case the result tuples (from the
|
|
topmost unique/join/whatever node) have to be skipped.
|
|
|
|
With these enhancements, the index tuples to be skipped
|
|
(offset) will still be scanned, but not the data tuples they
|
|
point to. Index scanning might be somewhat faster.
|
|
|
|
This all will only speedup simple 1-table-queries, no joins
|
|
or if the requested order isn't that what the index exactly
|
|
returns.
|
|
|
|
Anyway, I'll take a look if I can change the planner to omit
|
|
the sort if the tests described above are true. I think it
|
|
would be good anyway.
|
|
|
|
|
|
Jan
|
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|
|
--
|
|
|
|
#======================================================================#
|
|
# It's easier to get forgiveness for being wrong than for being right. #
|
|
# Let's break this rule - forgive me. #
|
|
#======================================== jwieck@debis.com (Jan Wieck) #
|
|
|
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|
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|
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From owner-pgsql-hackers@hub.org Wed Oct 14 11:01:36 1998
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Message-Id: <m0zTS0m-000EBRC@orion.SAPserv.Hamburg.dsh.de>
|
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From: jwieck@debis.com (Jan Wieck)
|
|
Subject: Re: [HACKERS] What about LIMIT in SELECT ?
|
|
To: lockhart@alumni.caltech.edu (Thomas G. Lockhart)
|
|
Date: Wed, 14 Oct 1998 16:34:47 +0200 (MET DST)
|
|
Cc: jwieck@debis.com, eric@linux-hw.com, jeff@remapcorp.com,
|
|
hackers@postgreSQL.org
|
|
Reply-To: jwieck@debis.com (Jan Wieck)
|
|
In-Reply-To: <3624AE5C.752E4E7F@alumni.caltech.edu> from "Thomas G. Lockhart" at Oct 14, 98 01:59:56 pm
|
|
X-Mailer: ELM [version 2.4 PL25]
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Content-Type: text
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Sender: owner-pgsql-hackers@postgreSQL.org
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Precedence: bulk
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Status: RO
|
|
|
|
>
|
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> > SELECT * FROM tab WHERE key > 'G' ORDER BY key;
|
|
> > results in a sort->indexscan - hmmm.
|
|
> > The last one is the query we would need in the web
|
|
> > environment used over a cursor as in the example above. But
|
|
> > due to the sort, the backend selects until the end of the
|
|
> > table, sorts them and then returns only the first 20 rows
|
|
> > (out of sorts result).
|
|
>
|
|
> So you are saying that for this last case the sort was unnecessary? Does
|
|
> the backend traverse the index in the correct order to guarantee that
|
|
> the tuples are coming out already sorted? Does a hash index give the
|
|
> same plan (I would expect a sort->seqscan for a hash index)?
|
|
|
|
Good point! As far as I can see, the planner chooses index
|
|
usage only depending on the WHERE clause. A hash index is
|
|
only usable when the given qualification uses = on the
|
|
indexed attribute(s).
|
|
|
|
If the sortClause exactly matches the indexed attributes of
|
|
the ONE used btree index and all operators request ascending
|
|
order I think the index scan already returns the correct
|
|
order. Who know's definitely?
|
|
|
|
Addition to my last posting: ... and if the index scan is
|
|
using a btree index ...
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|
|
|
|
Jan
|
|
|
|
--
|
|
|
|
#======================================================================#
|
|
# It's easier to get forgiveness for being wrong than for being right. #
|
|
# Let's break this rule - forgive me. #
|
|
#======================================== jwieck@debis.com (Jan Wieck) #
|
|
|
|
|
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|
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|
|
From owner-pgsql-hackers@hub.org Wed Oct 14 13:55:58 1998
|
|
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Wed, 14 Oct 1998 13:21:15 -0400 (EDT)
|
|
From: Bruce Momjian <maillist@candle.pha.pa.us>
|
|
Message-Id: <199810141721.NAA28746@candle.pha.pa.us>
|
|
Subject: Re: [HACKERS] What about LIMIT in SELECT ?
|
|
In-Reply-To: <3624AE5C.752E4E7F@alumni.caltech.edu> from "Thomas G. Lockhart" at "Oct 14, 1998 1:59:56 pm"
|
|
To: lockhart@alumni.caltech.edu (Thomas G. Lockhart)
|
|
Date: Wed, 14 Oct 1998 13:21:15 -0400 (EDT)
|
|
Cc: jwieck@debis.com, eric@linux-hw.com, jeff@remapcorp.com,
|
|
hackers@postgreSQL.org
|
|
X-Mailer: ELM [version 2.4ME+ PL47 (25)]
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Status: ROr
|
|
|
|
> > I've done some tests and what I found out might be a bug in
|
|
> > PostgreSQL's query optimizer.
|
|
> > SELECT * FROM tab ORDER BY key;
|
|
> > results in a sort->seqscan - I would have
|
|
> > expected an indexscan!
|
|
>
|
|
> Given that a table _could_ be completely unsorted on disk, it is
|
|
> probably reasonable to suck the data in for a possible in-memory sort
|
|
> rather than skipping around the disk to pick up individual tuples via
|
|
> the index. Don't know if vacuum has a statistic on "orderness"...
|
|
|
|
Thomas is correct on this. Vadim has run some tests, and with our
|
|
optimized psort() code, the in-memory sort is often faster than using
|
|
the index to get the tuple, because you are jumping all over the drive.
|
|
I don't remember, but obviously there is a break-even point where
|
|
getting X rows using the index on a table of Y rows is faster , but
|
|
getting X+1 rows on a table of Y rows is faster getting all the rows
|
|
sequentailly, and doing the sort.
|
|
|
|
You would have to pick only certain queries(no joins, index matches
|
|
ORDER BY), take the number of rows requested, and the number of rows
|
|
selected, and figure out if it is faster to use the index, or a
|
|
sequential scan and do the ORDER BY yourself.
|
|
|
|
|
|
Add to this the OFFSET capability. I am not sure how you are going to
|
|
get into the index and start at the n-th entry, unless perhaps you just
|
|
sequential scan the index.
|
|
|
|
In fact, many queries just get column already indexed, and we could just
|
|
pull the data right out of the index.
|
|
|
|
I have added this to the TODO list:
|
|
|
|
* Pull requested data directly from indexes, bypassing heap data
|
|
|
|
I think this has to be post-6.4 work, but I think we need to work in
|
|
this direction. I am holding off any cnfify fixes for post-6.4, but a
|
|
6.4.1 performance release certainly is possible.
|
|
|
|
|
|
But, you are correct that certain cases where in index is already being
|
|
used on a query, you could just skip the sort IF you used the index to
|
|
get the rows from the base table.
|
|
|
|
--
|
|
Bruce Momjian | http://www.op.net/~candle
|
|
maillist@candle.pha.pa.us | (610) 853-3000
|
|
+ If your life is a hard drive, | 830 Blythe Avenue
|
|
+ Christ can be your backup. | Drexel Hill, Pennsylvania 19026
|
|
|
|
|
|
From owner-pgsql-hackers@hub.org Wed Oct 14 13:55:59 1998
|
|
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Wed, 14 Oct 1998 13:21:51 -0400
|
|
Date: Wed, 14 Oct 1998 13:21:51 -0400 (EDT)
|
|
From: Terry Mackintosh <terry@terrym.com>
|
|
X-Sender: terry@terry1.acun.com
|
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To: Jeff Hoffmann <jeff@remapcorp.com>
|
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cc: PostgreSQL-development <hackers@postgreSQL.org>
|
|
Subject: Re: [HACKERS] What about LIMIT in SELECT ?
|
|
In-Reply-To: <005101bdf6de$f9345150$c525c4ce@go-to-jail.remapcorp.com>
|
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Message-ID: <Pine.LNX.3.95.981014130857.14397B-100000@terry1.acun.com>
|
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|
|
|
|
On Tue, 13 Oct 1998, Jeff Hoffmann wrote:
|
|
|
|
> >Hi, my 2 cents...
|
|
> >
|
|
> >I agree completely, LIMIT would be VERY usefull in web based apps, which
|
|
> >is all I run. It does not matter to me if it is not part of a formal
|
|
> >standard. The idea is so common that it is a defacto standard.
|
|
>
|
|
> i'm not familiar with mysql and using "LIMIT" but wouldn't this same effect
|
|
> be achieved by declaring a cursor and fetching however many records in the
|
|
> cursor? it's a very noticeable improvement when you only want the first 20
|
|
> out of 500 in a 200k record database, at least.
|
|
|
|
Yes, while this is an improvement, it still has to do the entire query,
|
|
would be nice if the query could be terminated after a designated number
|
|
of rows where found, thus freeing system resources that are other wise
|
|
consumed.
|
|
I have seen web users run ridculous querys, like search for the
|
|
letter 'a', and it happens to be a substring search, now the box go'es ape
|
|
shit for 5 or 10 min.s while it basically gets the whole db as the search
|
|
result. All this befor you can do a 'FETCH', as I understand FETCH, I
|
|
will need to read up on it.
|
|
|
|
Note that I do not have any databases that larg on my box, I was thinking
|
|
back to my VFP/NT experiances.
|
|
|
|
Have a great day
|
|
Terry Mackintosh <terry@terrym.com> http://www.terrym.com
|
|
sysadmin/owner Please! No MIME encoded or HTML mail, unless needed.
|
|
|
|
Proudly powered by R H Linux 4.2, Apache 1.3, PHP 3, PostgreSQL 6.3
|
|
-------------------------------------------------------------------
|
|
Success Is A Choice ... book by Rick Patino, get it, read it!
|
|
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|
|
From owner-pgsql-hackers@hub.org Wed Oct 14 13:59:05 1998
|
|
Received: from hub.org (majordom@hub.org [209.47.148.200])
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|
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|
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Date: Wed, 14 Oct 1998 13:41:24 -0400 (EDT)
|
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From: Terry Mackintosh <terry@terrym.com>
|
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|
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To: PostgreSQL-development <hackers@postgreSQL.org>
|
|
Subject: Re: [HACKERS] What about LIMIT in SELECT ?
|
|
In-Reply-To: <199810132116.RAA11249@candle.pha.pa.us>
|
|
Message-ID: <Pine.LNX.3.95.981014133641.14397D-100000@terry1.acun.com>
|
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|
|
|
On Tue, 13 Oct 1998, Bruce Momjian wrote:
|
|
|
|
> What we could do is _if_ there is only one table(no joins), and an index
|
|
> exists that matches the ORDER BY, we could use the index to
|
|
> short-circuit the query.
|
|
>
|
|
> I have added this item to the TODO list:
|
|
>
|
|
> * Allow LIMIT ability on single-table queries that have no ORDER BY or
|
|
> a matching index
|
|
>
|
|
> This looks do-able, and a real win. Would this make web applications
|
|
> happier? If there is an ORDER BY and no index, or a join, I can't
|
|
> figure out how we would short-circuit the query.
|
|
>
|
|
Yes, this would do for most of my apps.
|
|
It may just be my lack of sophistication, but I find that most web apps
|
|
are very simple in nature/table layout, and thus queries are often on only
|
|
a single table.
|
|
|
|
Thanks
|
|
Terry Mackintosh <terry@terrym.com> http://www.terrym.com
|
|
sysadmin/owner Please! No MIME encoded or HTML mail, unless needed.
|
|
|
|
Proudly powered by R H Linux 4.2, Apache 1.3, PHP 3, PostgreSQL 6.3
|
|
-------------------------------------------------------------------
|
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Success Is A Choice ... book by Rick Patino, get it, read it!
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From wieck@sapserv.debis.de Wed Oct 14 13:55:53 1998
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Message-Id: <m0zTVAt-000EBRC@orion.SAPserv.Hamburg.dsh.de>
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From: jwieck@debis.com (Jan Wieck)
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Subject: Re: [HACKERS] What about LIMIT in SELECT ?
|
|
To: maillist@candle.pha.pa.us (Bruce Momjian)
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Date: Wed, 14 Oct 1998 19:57:27 +0200 (MET DST)
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Cc: lockhart@alumni.caltech.edu, jwieck@debis.com, eric@linux-hw.com,
|
|
jeff@remapcorp.com, hackers@postgreSQL.org
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Reply-To: jwieck@debis.com (Jan Wieck)
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|
In-Reply-To: <199810141721.NAA28746@candle.pha.pa.us> from "Bruce Momjian" at Oct 14, 98 01:21:15 pm
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X-Mailer: ELM [version 2.4 PL25]
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Content-Type: text
|
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Status: RO
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> But, you are correct that certain cases where in index is already being
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> used on a query, you could just skip the sort IF you used the index to
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> get the rows from the base table.
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Especially in the case where
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SELECT ... WHERE key > 'val' ORDER BY key;
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creates a Sort->IndexScan plan. The index scan already jumps
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around on the disc to collect the sorts input and the sort
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finally returns exactly the same output (if the used index is
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|
only on key).
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And this is the case for large tables. The planner first
|
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decides to use an index scan due to the WHERE clause and
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later it notices the ORDER BY clause and creates a sort over
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the scan.
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I'm actually hacking around on it to see what happens if I
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suppress the sort node in some cases.
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Jan
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--
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#======================================================================#
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# It's easier to get forgiveness for being wrong than for being right. #
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# Let's break this rule - forgive me. #
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#======================================== jwieck@debis.com (Jan Wieck) #
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From owner-pgsql-hackers@hub.org Wed Oct 14 16:31:07 1998
|
|
Received: from renoir.op.net (root@renoir.op.net [209.152.193.4])
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by candle.pha.pa.us (8.9.0/8.9.0) id OAA29639;
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Wed, 14 Oct 1998 14:27:05 -0400 (EDT)
|
|
From: Bruce Momjian <maillist@candle.pha.pa.us>
|
|
Message-Id: <199810141827.OAA29639@candle.pha.pa.us>
|
|
Subject: Re: [HACKERS] What about LIMIT in SELECT ?
|
|
In-Reply-To: <199810141721.NAA28746@candle.pha.pa.us> from Bruce Momjian at "Oct 14, 1998 1:21:15 pm"
|
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To: maillist@candle.pha.pa.us (Bruce Momjian)
|
|
Date: Wed, 14 Oct 1998 14:27:05 -0400 (EDT)
|
|
Cc: lockhart@alumni.caltech.edu, jwieck@debis.com, eric@linux-hw.com,
|
|
jeff@remapcorp.com, hackers@postgreSQL.org
|
|
X-Mailer: ELM [version 2.4ME+ PL47 (25)]
|
|
MIME-Version: 1.0
|
|
Content-Type: text/plain; charset=US-ASCII
|
|
Content-Transfer-Encoding: 7bit
|
|
Sender: owner-pgsql-hackers@postgreSQL.org
|
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Precedence: bulk
|
|
Status: RO
|
|
|
|
> Thomas is correct on this. Vadim has run some tests, and with our
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|
> optimized psort() code, the in-memory sort is often faster than using
|
|
> the index to get the tuple, because you are jumping all over the drive.
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|
> I don't remember, but obviously there is a break-even point where
|
|
> getting X rows using the index on a table of Y rows is faster , but
|
|
> getting X+1 rows on a table of Y rows is faster getting all the rows
|
|
> sequentailly, and doing the sort.
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|
>
|
|
> You would have to pick only certain queries(no joins, index matches
|
|
> ORDER BY), take the number of rows requested, and the number of rows
|
|
> selected, and figure out if it is faster to use the index, or a
|
|
> sequential scan and do the ORDER BY yourself.
|
|
>
|
|
> Add to this the OFFSET capability. I am not sure how you are going to
|
|
> get into the index and start at the n-th entry, unless perhaps you just
|
|
> sequential scan the index.
|
|
>
|
|
> In fact, many queries just get column already indexed, and we could just
|
|
> pull the data right out of the index.
|
|
>
|
|
> I have added this to the TODO list:
|
|
>
|
|
> * Pull requested data directly from indexes, bypassing heap data
|
|
>
|
|
> I think this has to be post-6.4 work, but I think we need to work in
|
|
> this direction. I am holding off any cnfify fixes for post-6.4, but a
|
|
> 6.4.1 performance release certainly is possible.
|
|
>
|
|
>
|
|
> But, you are correct that certain cases where in index is already being
|
|
> used on a query, you could just skip the sort IF you used the index to
|
|
> get the rows from the base table.
|
|
|
|
I have had more time to think about this. Basically, for pre-sorted
|
|
data, our psort code is very fast, because it does not need to sort
|
|
anything. It just moves the rows in and out of the sort memory. Yes,
|
|
it could be removed in some cases, and probably should be, but it is not
|
|
going to produce great speedups.
|
|
|
|
The more general case I will describe below.
|
|
|
|
First, let's look at a normal query:
|
|
|
|
SELECT *
|
|
FROM tab
|
|
ORDER BY col1
|
|
|
|
This is not going to use an index, and probably should not because it is
|
|
faster for large tables to sort them in memory, rather than moving all
|
|
over the disk. For small tables, if the entire table fits in the buffer
|
|
cache, it may be faster to use the index, but on a small table the sort
|
|
doesn't take very long either, and the buffer cache effectiveness is
|
|
affected by other backends using it, so it may be better not to count on
|
|
it for a speedup.
|
|
|
|
However, if you only want the first 10 rows, that is a different story.
|
|
We pull all the rows into the backend, sort them, then return 10 rows.
|
|
The query, if we could do it, should be written as:
|
|
|
|
SELECT *
|
|
FROM tab
|
|
WHERE col1 < some_unknown_value
|
|
ORDER BY col1
|
|
|
|
In this case, the optimizer looks at the column statistics, and properly
|
|
uses an index to pull only a small subset of the table. This is the
|
|
type of behavior people want for queries returning only a few values.
|
|
|
|
But, unfortunately, we don't know that mystery value.
|
|
|
|
Now, everyone agrees we need an index matching the ORDER BY to make this
|
|
query quick, but we don't know that mystery value, so currently we
|
|
execute the whole query, and do a fetch.
|
|
|
|
What I am now thinking is that maybe we need a way to walk around that
|
|
index. Someone months ago asked how to do that, and we told him he
|
|
couldn't, because this not a C-ISAM/dbm type database. However, if we
|
|
could somehow pass into the query the index location we want to start
|
|
at, and how many rows we need, that would solve our problem, and perhaps
|
|
even allow joined queries to work, assuming the table in the ORDER BY is
|
|
in an outer join loop.
|
|
|
|
SELECT *
|
|
FROM tab
|
|
WHERE col1 < some_unknown_value
|
|
ORDER BY col1
|
|
USING INDEX tab_idx(452) COUNT 100
|
|
|
|
where 452 is an 452th index entry, and COUNT is the number of index rows
|
|
you want to process. The query may return more or less than 100 rows if
|
|
there is a join and it joins to zero or more than one row in the joined
|
|
table, but this seems like perhaps a good way to go at it. We need to
|
|
do it this way because if a single index row returns 4 result rows, and
|
|
only two of the four rows fit in the number of rows returnd as set by the
|
|
user, it is hard to re-start the query at the proper point, because you
|
|
would have to process the index rows a second time, and return just part
|
|
of the result, and that is hard.
|
|
|
|
If the index changes, or rows are added, the results are going to be
|
|
unreliable, but that is probably going to be true of any state-less
|
|
implementation we can devise.
|
|
|
|
I think this may be fairly easy to implement. We could sequential scan
|
|
the index to get to the 452th row. That is going to be quick. We can
|
|
pass the 452 into the btree index code, so only a certain range of index
|
|
tuples are returned, and the system believes it has processed the entire
|
|
query, while we know it hasn't. Doesn't really work with hash, so we
|
|
will not allow it for those indexes.
|
|
|
|
To make it really easy, we could implement it as a 'SET' command, so we
|
|
don't actually have it as part of the query, and have to pass it around
|
|
through all the modules. You would do the proper 'SET' before running
|
|
the query. Optimizer would look at 'SET' value to force index use.
|
|
|
|
SET INDEX TO tab_idx START 452 COUNT 100
|
|
|
|
or
|
|
|
|
SET INDEX TO tab_idx FROM 452 COUNT 451
|
|
|
|
There would have to be some way to signal that the end of the index had
|
|
been reached, because returning zero rows is not enough of a guarantee
|
|
in a joined SELECT.
|
|
|
|
Comments?
|
|
|
|
--
|
|
Bruce Momjian | http://www.op.net/~candle
|
|
maillist@candle.pha.pa.us | (610) 853-3000
|
|
+ If your life is a hard drive, | 830 Blythe Avenue
|
|
+ Christ can be your backup. | Drexel Hill, Pennsylvania 19026
|
|
|
|
|
|
From owner-pgsql-hackers@hub.org Wed Oct 14 17:31:23 1998
|
|
Received: from renoir.op.net (root@renoir.op.net [209.152.193.4])
|
|
by candle.pha.pa.us (8.9.0/8.9.0) with ESMTP id RAA01591
|
|
for <maillist@candle.pha.pa.us>; Wed, 14 Oct 1998 17:31:21 -0400 (EDT)
|
|
Received: from hub.org (majordom@hub.org [209.47.148.200]) by renoir.op.net (o1/$ Revision: 1.18 $) with ESMTP id RAA02744 for <maillist@candle.pha.pa.us>; Wed, 14 Oct 1998 17:26:53 -0400 (EDT)
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Received: from localhost (majordom@localhost)
|
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by hub.org (8.8.8/8.8.8) with SMTP id RAA05601;
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Wed, 14 Oct 1998 17:03:21 -0400 (EDT)
|
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(envelope-from owner-pgsql-hackers@hub.org)
|
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Received: by hub.org (TLB v0.10a (1.23 tibbs 1997/01/09 00:29:32)); Wed, 14 Oct 1998 16:59:54 +0000 (EDT)
|
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Received: (from majordom@localhost)
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|
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|
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X-Authentication-Warning: hub.org: majordom set sender to owner-pgsql-hackers@postgreSQL.org using -f
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|
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for <hackers@postgreSQL.org>; Wed, 14 Oct 1998 16:59:28 -0400 (EDT)
|
|
(envelope-from wieck@sapserv.debis.de)
|
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|
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|
|
id m0zTVYr-000B5AC; Wed, 14 Oct 98 20:22 MET DST
|
|
Received: by orion.SAPserv.Hamburg.dsh.de
|
|
for lockhart@alumni.caltech.edu
|
|
id m0zTY6V-000EBRC; Wed, 14 Oct 98 23:05 MET DST
|
|
Message-Id: <m0zTY6V-000EBRC@orion.SAPserv.Hamburg.dsh.de>
|
|
From: jwieck@debis.com (Jan Wieck)
|
|
Subject: Re: [HACKERS] What about LIMIT in SELECT ?
|
|
To: maillist@candle.pha.pa.us (Bruce Momjian)
|
|
Date: Wed, 14 Oct 1998 23:05:07 +0200 (MET DST)
|
|
Cc: maillist@candle.pha.pa.us, lockhart@alumni.caltech.edu, jwieck@debis.com,
|
|
eric@linux-hw.com, jeff@remapcorp.com, hackers@postgreSQL.org
|
|
Reply-To: jwieck@debis.com (Jan Wieck)
|
|
In-Reply-To: <199810141827.OAA29639@candle.pha.pa.us> from "Bruce Momjian" at Oct 14, 98 02:27:05 pm
|
|
X-Mailer: ELM [version 2.4 PL25]
|
|
Content-Type: text
|
|
Sender: owner-pgsql-hackers@postgreSQL.org
|
|
Precedence: bulk
|
|
Status: ROr
|
|
|
|
> I have had more time to think about this. Basically, for pre-sorted
|
|
> data, our psort code is very fast, because it does not need to sort
|
|
> anything. It just moves the rows in and out of the sort memory. Yes,
|
|
> it could be removed in some cases, and probably should be, but it is not
|
|
> going to produce great speedups.
|
|
|
|
And I got the time to hack around about this.
|
|
|
|
I hacked in a little check into the planner, that compares
|
|
the sortClause against the key field list of an index scan
|
|
and just suppresses the sort node if it exactly matchs and
|
|
all sort operators are "<".
|
|
|
|
I tested with a 10k row table where key is a text field. The
|
|
base query is a
|
|
|
|
SELECT ... WHERE key > 'val' ORDER BY key;
|
|
|
|
The used 'val' is always a key that is close to the first of
|
|
all keys in the table ('' on the first query and the last
|
|
selected value on subsequent ones).
|
|
|
|
Scenario 1 (S1) uses exactly the above query but processes
|
|
only the first 20 rows from the result buffer. Thus the
|
|
frontend receives nearly the whole table.
|
|
|
|
Scenario 2 (S2) uses a cursor and FETCH 20. But closes the
|
|
cursor and creates a new one for the next selection (only
|
|
with another 'val') as it would occur in a web application.
|
|
|
|
If there is no index on key, the backend will allways do a
|
|
Sort->SeqScan and due to the 'val' close to the lowest
|
|
existing key nearly all tuples get scanned and put into the
|
|
sort. S1 here runs about 10 seconds and S2 about 6 seconds.
|
|
The speedup in S2 results from the reduced overhead of
|
|
sending not wanted tuples into the frontend.
|
|
|
|
Now with a btree index on key and an unpatched backend.
|
|
Produced plan is always a Sort->IndexScan. S1 needs 16
|
|
seconds and S2 needs 12 seconds. Again nearly all data is put
|
|
into the sort but this time over the index scan and that is
|
|
slower.
|
|
|
|
Last with the btree index on key and the patched backend.
|
|
This time the plan is a plain IndexScan because the ORDER BY
|
|
clause exactly matches the sort order of the choosen index.
|
|
S1 needs 13 seconds and S2 less than 0.2! This dramatic
|
|
speedup comes from the fact, that this time the index scan is
|
|
the toplevel executor node and the executor run is stopped
|
|
after 20 tuples have been selected.
|
|
|
|
Analysis of the above timings:
|
|
|
|
If there is an ORDER BY clause, using an index scan is the
|
|
clever way if the indexqual dramatically reduces the the
|
|
amount of data selected and sorted. I think this is the
|
|
normal case (who really selects nearly all rows from a 5M row
|
|
table?). So choosing the index path is correct. This will
|
|
hurt if someone really selects most of the rows and the index
|
|
scan jumps over the disc. But here the programmer should use
|
|
an unqualified query to perform a seqscan and do the
|
|
qualification in the frontend application.
|
|
|
|
The speedup for the cursor/fetch scenario is so impressive
|
|
that I'll create a post 6.4 patch. I don't want it in 6.4
|
|
because there is absolutely no query in the whole regression
|
|
test, where it suppresses the sort node. So we have
|
|
absolutely no check that it doesn't break anything.
|
|
|
|
For a web application, that can use a unique key to select
|
|
the next amount of rows, it will be a big win.
|
|
|
|
|
|
Jan
|
|
|
|
--
|
|
|
|
#======================================================================#
|
|
# It's easier to get forgiveness for being wrong than for being right. #
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# Let's break this rule - forgive me. #
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#======================================== jwieck@debis.com (Jan Wieck) #
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From owner-pgsql-hackers@hub.org Thu Oct 15 00:01:10 1998
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Message-Id: <199810150234.LAA08260@srapc451.sra.co.jp>
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To: jwieck@debis.com (Jan Wieck)
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cc: oleg@sai.msu.su, hackers@postgreSQL.org, t-ishii@sra.co.jp
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Subject: Re: [HACKERS] What about LIMIT in SELECT ?
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From: Tatsuo Ishii <t-ishii@sra.co.jp>
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Reply-To: t-ishii@sra.co.jp
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In-reply-to: Your message of Wed, 14 Oct 1998 16:24:56 +0200.
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<m0zTRrE-000EBRC@orion.SAPserv.Hamburg.dsh.de>
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Date: Thu, 15 Oct 1998 11:34:54 +0900
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Sender: owner-pgsql-hackers@postgreSQL.org
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Precedence: bulk
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Status: RO
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>> postgres just because of lacking LIMIT. Tatsuo posted a patch
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>> for set query_limit to 'num', I just tested it and seems it
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>> works fine. Now, we need only possibility to specify offset,
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>> say
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>> set query_limit to 'offset,num'
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>> ( Tatsuo, How difficult to do this ?)
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>> and LIMIT problem will ne gone.
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>
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> Think you haven't read my posting completely. Even with the
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> executor limit, the complete scan into the sort is done by
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> the backend. You need to specify ORDER BY to get the same
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> list again (without the offset doesn't make sense). But
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> currently, ORDER BY forces a sort node into the query plan.
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I think we have understanded your point. set query_limit is just a
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easy alternative of using cursor and fetch.
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> I haven't looked at Tatsuo's patch very well. But if it
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> limits the amount of data going into the sort (on ORDER BY),
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> it will break it! The requested ordering could be different
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> from what the choosen index might return. The used index is
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> choosen by the planner upon the qualifications given, not the
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> ordering wanted.
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I think it limits the final result. When query_limit is set,
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the arg "numberTuples" of ExecutePlan() is set to it instead of 0
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(this means no limit).
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Talking about "offset," it shouldn't be very difficult. I guess all we
|
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have to do is adding a new arg "offset" to ExecutePlan() then making
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obvious modifications. (and of course we have to modify set
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query_limit syntax but it's trivial)
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However, before going ahead, I would like to ask other hackers about
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this direction. This might be convenient for some users, but still the
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essential performance issue would remain. In another word, this is a
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short-term solution not a intrinsic one, IMHO.
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--
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Tatsuo Ishii
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t-ishii@sra.co.jp
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From owner-pgsql-hackers@hub.org Thu Oct 15 10:01:17 1998
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Message-Id: <m0zTmRT-000EBRC@orion.SAPserv.Hamburg.dsh.de>
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From: jwieck@debis.com (Jan Wieck)
|
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Subject: Re: [HACKERS] What about LIMIT in SELECT ?
|
|
To: t-ishii@sra.co.jp
|
|
Date: Thu, 15 Oct 1998 14:23:43 +0200 (MET DST)
|
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Cc: jwieck@debis.com, oleg@sai.msu.su, hackers@postgreSQL.org
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Reply-To: jwieck@debis.com (Jan Wieck)
|
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In-Reply-To: <199810150234.LAA08260@srapc451.sra.co.jp> from "Tatsuo Ishii" at Oct 15, 98 11:34:54 am
|
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X-Mailer: ELM [version 2.4 PL25]
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Content-Type: text
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Sender: owner-pgsql-hackers@postgreSQL.org
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Precedence: bulk
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Status: RO
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|
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Tatsuo Ishii wrote:
|
|
|
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> I think we have understanded your point. set query_limit is just a
|
|
> easy alternative of using cursor and fetch.
|
|
>
|
|
> > I haven't looked at Tatsuo's patch very well. But if it
|
|
> > limits the amount of data going into the sort (on ORDER BY),
|
|
> > it will break it! The requested ordering could be different
|
|
> > from what the choosen index might return. The used index is
|
|
> > choosen by the planner upon the qualifications given, not the
|
|
> > ordering wanted.
|
|
>
|
|
> I think it limits the final result. When query_limit is set,
|
|
> the arg "numberTuples" of ExecutePlan() is set to it instead of 0
|
|
> (this means no limit).
|
|
>
|
|
> Talking about "offset," it shouldn't be very difficult. I guess all we
|
|
> have to do is adding a new arg "offset" to ExecutePlan() then making
|
|
> obvious modifications. (and of course we have to modify set
|
|
> query_limit syntax but it's trivial)
|
|
|
|
The offset could become
|
|
|
|
FETCH n IN cursor [OFFSET n];
|
|
|
|
and
|
|
|
|
SELECT ... [LIMIT offset,count];
|
|
|
|
The FETCH command already calls ExecutorRun() with the given
|
|
count (the tuple limit). Telling it the offset too is really
|
|
simple. And ExecutorRun() could check if the toplevel
|
|
executor node is an index scan. Skipping tuples during the
|
|
index scan requires, that all qualifications are in the
|
|
indexqual, thus any tuple returned by it will become a final
|
|
result row (as it would be in the simple 1-table-queries we
|
|
discussed). If that isn't the case, the executor must
|
|
fallback to skip the final result tuples and that is after an
|
|
eventually processed sort/merge of the complete result set.
|
|
That would only reduce communication to the client and memory
|
|
required there to buffer the result set (not a bad thing
|
|
either).
|
|
|
|
ProcessQueryDesc() in tcop/pquery.c also calls ExecutorRun()
|
|
but with a constant 0 tuple count. Having offset and count in
|
|
the parsetree would make it without any state variables or
|
|
SET command. And it's the only clean way to restrict LIMIT to
|
|
SELECT queries. Any thrown in LIMIT to ExecutorRun() from
|
|
another place could badly hurt the rewrite system. Remember
|
|
that non-instead actions on insert/update/delete are
|
|
processed before the original query! And what about SQL
|
|
functions that get processed during the evaluation of another
|
|
query (view using an SQL function for count(*))?
|
|
|
|
A little better would it be to make the LIMIT values able to
|
|
be parameter nodes. C or PL functions use the prepared plan
|
|
feature of the SPI manager for performance reasons.
|
|
Especially the offset value might there need to be a
|
|
parameter that the executor has to pick out first. If we
|
|
change the count argument of ExecutorRun to a List *limit,
|
|
this one could be NIL (to mean the old 0 count 0 offset
|
|
behaviour) or a list of two elements that both can be either
|
|
a Const or a Param of type int4. Easy for the executor to
|
|
evaluate.
|
|
|
|
The only places where ExecutorRun() is called are
|
|
tcop/pquery.c (queries from frontend), commands/command.c
|
|
(FETCH command), executor/functions.c (SQL functions) and
|
|
executor/spi.c (SPI manager). So it is easy to change the
|
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call interface too.
|
|
|
|
|
|
Jan
|
|
|
|
--
|
|
|
|
#======================================================================#
|
|
# It's easier to get forgiveness for being wrong than for being right. #
|
|
# Let's break this rule - forgive me. #
|
|
#======================================== jwieck@debis.com (Jan Wieck) #
|
|
|
|
|
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|
|
|
|
From owner-pgsql-hackers@hub.org Thu Oct 15 14:32:34 1998
|
|
Received: from renoir.op.net (root@renoir.op.net [209.152.193.4])
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Thu, 15 Oct 1998 19:01:23 +0300 (MSK)
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Date: Thu, 15 Oct 1998 20:01:23 +0400 (MSD)
|
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From: Oleg Bartunov <oleg@sai.msu.su>
|
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X-Sender: megera@ra
|
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To: Jan Wieck <jwieck@debis.com>
|
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cc: t-ishii@sra.co.jp, hackers@postgreSQL.org
|
|
Subject: Re: [HACKERS] What about LIMIT in SELECT ?
|
|
In-Reply-To: <m0zTmRT-000EBRC@orion.SAPserv.Hamburg.dsh.de>
|
|
Message-ID: <Pine.GSO.3.96.SK.981015193853.19322D-100000@ra>
|
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Organization: Sternberg Astronomical Institute (Moscow University)
|
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MIME-Version: 1.0
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Content-Type: TEXT/PLAIN; charset=US-ASCII
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Sender: owner-pgsql-hackers@postgreSQL.org
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Precedence: bulk
|
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Status: ROr
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This is a little bit off-topic,
|
|
I did some timings with latest cvs on my real database
|
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( all output redirected to /dev/null ), table contains 8798 records,
|
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31 columns, order key have indices.
|
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|
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1.select count(*) from work_flats;
|
|
0.02user 0.00system 0:00.18elapsed 10%CPU (0avgtext+0avgdata 0maxresident)k
|
|
0inputs+0outputs (131major+21minor)pagefaults 0swaps
|
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|
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2.select * from work_flats order by rooms, metro_id;
|
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2.35user 0.25system 0:10.11elapsed 25%CPU (0avgtext+0avgdata 0maxresident)k
|
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0inputs+0outputs (131major+2799minor)pagefaults 0swaps
|
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|
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3.set query_limit to '150';
|
|
SET VARIABLE
|
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select * from work_flats order by rooms, metro_id;
|
|
0.06user 0.00system 0:02.75elapsed 2%CPU (0avgtext+0avgdata 0maxresident)k
|
|
0inputs+0outputs (131major+67minor)pagefaults 0swaps
|
|
|
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4.begin;
|
|
declare tt cursor for
|
|
select * from work_flats order by rooms, metro_id;
|
|
fetch 150 in tt;
|
|
end;
|
|
0.05user 0.01system 0:02.76elapsed 2%CPU (0avgtext+0avgdata 0maxresident)k
|
|
0inputs+0outputs (131major+67minor)pagefaults 0swaps
|
|
|
|
As you can see timings for query_limit and cursor are very similar,
|
|
I didn't expected this. So, in principle, enhanced version of fetch
|
|
(with offset) would cover all we need from LIMIT, but query_limit would be
|
|
still useful, for example to restrict loadness of server.
|
|
Will all enhancements you discussed go to the 6.4 ?
|
|
I'm really interested in testing this stuff because I begin new project
|
|
and everything we discussed here are badly needed.
|
|
|
|
|
|
Regards,
|
|
|
|
Oleg
|
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|
|
|
|
|
|
On Thu, 15 Oct 1998, Jan Wieck wrote:
|
|
|
|
> Date: Thu, 15 Oct 1998 14:23:43 +0200 (MET DST)
|
|
> From: Jan Wieck <jwieck@debis.com>
|
|
> To: t-ishii@sra.co.jp
|
|
> Cc: jwieck@debis.com, oleg@sai.msu.su, hackers@postgreSQL.org
|
|
> Subject: Re: [HACKERS] What about LIMIT in SELECT ?
|
|
>
|
|
> Tatsuo Ishii wrote:
|
|
>
|
|
> > I think we have understanded your point. set query_limit is just a
|
|
> > easy alternative of using cursor and fetch.
|
|
> >
|
|
> > > I haven't looked at Tatsuo's patch very well. But if it
|
|
> > > limits the amount of data going into the sort (on ORDER BY),
|
|
> > > it will break it! The requested ordering could be different
|
|
> > > from what the choosen index might return. The used index is
|
|
> > > choosen by the planner upon the qualifications given, not the
|
|
> > > ordering wanted.
|
|
> >
|
|
> > I think it limits the final result. When query_limit is set,
|
|
> > the arg "numberTuples" of ExecutePlan() is set to it instead of 0
|
|
> > (this means no limit).
|
|
> >
|
|
> > Talking about "offset," it shouldn't be very difficult. I guess all we
|
|
> > have to do is adding a new arg "offset" to ExecutePlan() then making
|
|
> > obvious modifications. (and of course we have to modify set
|
|
> > query_limit syntax but it's trivial)
|
|
>
|
|
> The offset could become
|
|
>
|
|
> FETCH n IN cursor [OFFSET n];
|
|
>
|
|
> and
|
|
>
|
|
> SELECT ... [LIMIT offset,count];
|
|
>
|
|
> The FETCH command already calls ExecutorRun() with the given
|
|
> count (the tuple limit). Telling it the offset too is really
|
|
> simple. And ExecutorRun() could check if the toplevel
|
|
> executor node is an index scan. Skipping tuples during the
|
|
> index scan requires, that all qualifications are in the
|
|
> indexqual, thus any tuple returned by it will become a final
|
|
> result row (as it would be in the simple 1-table-queries we
|
|
> discussed). If that isn't the case, the executor must
|
|
> fallback to skip the final result tuples and that is after an
|
|
> eventually processed sort/merge of the complete result set.
|
|
> That would only reduce communication to the client and memory
|
|
> required there to buffer the result set (not a bad thing
|
|
> either).
|
|
>
|
|
> ProcessQueryDesc() in tcop/pquery.c also calls ExecutorRun()
|
|
> but with a constant 0 tuple count. Having offset and count in
|
|
> the parsetree would make it without any state variables or
|
|
> SET command. And it's the only clean way to restrict LIMIT to
|
|
> SELECT queries. Any thrown in LIMIT to ExecutorRun() from
|
|
> another place could badly hurt the rewrite system. Remember
|
|
> that non-instead actions on insert/update/delete are
|
|
> processed before the original query! And what about SQL
|
|
> functions that get processed during the evaluation of another
|
|
> query (view using an SQL function for count(*))?
|
|
>
|
|
> A little better would it be to make the LIMIT values able to
|
|
> be parameter nodes. C or PL functions use the prepared plan
|
|
> feature of the SPI manager for performance reasons.
|
|
> Especially the offset value might there need to be a
|
|
> parameter that the executor has to pick out first. If we
|
|
> change the count argument of ExecutorRun to a List *limit,
|
|
> this one could be NIL (to mean the old 0 count 0 offset
|
|
> behaviour) or a list of two elements that both can be either
|
|
> a Const or a Param of type int4. Easy for the executor to
|
|
> evaluate.
|
|
>
|
|
> The only places where ExecutorRun() is called are
|
|
> tcop/pquery.c (queries from frontend), commands/command.c
|
|
> (FETCH command), executor/functions.c (SQL functions) and
|
|
> executor/spi.c (SPI manager). So it is easy to change the
|
|
> call interface too.
|
|
>
|
|
>
|
|
> Jan
|
|
>
|
|
> --
|
|
>
|
|
> #======================================================================#
|
|
> # It's easier to get forgiveness for being wrong than for being right. #
|
|
> # Let's break this rule - forgive me. #
|
|
> #======================================== jwieck@debis.com (Jan Wieck) #
|
|
>
|
|
>
|
|
|
|
_____________________________________________________________
|
|
Oleg Bartunov, sci.researcher, hostmaster of AstroNet,
|
|
Sternberg Astronomical Institute, Moscow University (Russia)
|
|
Internet: oleg@sai.msu.su, http://www.sai.msu.su/~megera/
|
|
phone: +007(095)939-16-83, +007(095)939-23-83
|
|
|
|
|
|
|
|
From owner-pgsql-hackers@hub.org Thu Oct 15 13:22:48 1998
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Message-Id: <m0zTqmM-000EBRC@orion.SAPserv.Hamburg.dsh.de>
|
|
From: jwieck@debis.com (Jan Wieck)
|
|
Subject: Re: [HACKERS] What about LIMIT in SELECT ?
|
|
To: hannu@trust.ee (Hannu Krosing)
|
|
Date: Thu, 15 Oct 1998 19:01:33 +0200 (MET DST)
|
|
Cc: jwieck@debis.com, pgsql-hackers@postgreSQL.org
|
|
Reply-To: jwieck@debis.com (Jan Wieck)
|
|
In-Reply-To: <36261DF7.D20368A0@trust.ee> from "Hannu Krosing" at Oct 15, 98 07:08:23 pm
|
|
X-Mailer: ELM [version 2.4 PL25]
|
|
Content-Type: text
|
|
Sender: owner-pgsql-hackers@postgreSQL.org
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|
Precedence: bulk
|
|
Status: RO
|
|
|
|
Hannu Krosing wrote:
|
|
|
|
> Jan Wieck wrote:
|
|
> > The speedup for the cursor/fetch scenario is so impressive
|
|
> > that I'll create a post 6.4 patch. I don't want it in 6.4
|
|
> > because there is absolutely no query in the whole regression
|
|
> > test, where it suppresses the sort node.
|
|
>
|
|
> Good, then it works as expected ;)
|
|
>
|
|
> More seriously, it is not within powers of current regression test
|
|
> framework to test speed improvements (only the case where
|
|
> performance-wise bad implementation will actually crash the backend,
|
|
> as in the cnfify problem, but AFAIK we dont test for those now)
|
|
>
|
|
> > So we have absolutely no check that it doesn't break anything.
|
|
>
|
|
> If it did pass the regression, then IMHO it did not break anything.
|
|
|
|
Thats the point. The check if the sort node is required
|
|
returns TRUE for ALL queries of the regression. So the
|
|
behaviour when it returns FALSE is absolutely not tested.
|
|
|
|
>
|
|
> I would vote for putting it in (maybe with a
|
|
> 'set fix_optimiser_stupidity on' safeguard to enable it). I see no
|
|
> reason to postpone it to 6.4.1 and force almost everybody to first
|
|
> patch their copy and then upgrade very soon.
|
|
>
|
|
> I would even go far enough to call it a bugfix, as it does not really
|
|
> introduce any new functionality only fixes some existing functionality
|
|
> so that much bigger databases can be actually used.
|
|
|
|
I can't call it a bugfix because it is only a performance win
|
|
in some situations. And I feel the risk is too high to put
|
|
untested code into the backend at BETA2 time. The max we
|
|
should do is to take this one and the LIMIT thing (maybe
|
|
implemented as I suggested lately), and put out a Web-
|
|
Performance-Release at the same time we release 6.4.
|
|
|
|
|
|
Jan
|
|
|
|
--
|
|
|
|
#======================================================================#
|
|
# It's easier to get forgiveness for being wrong than for being right. #
|
|
# Let's break this rule - forgive me. #
|
|
#======================================== jwieck@debis.com (Jan Wieck) #
|
|
|
|
|
|
|
|
|
|
From Inoue@tpf.co.jp Thu Oct 15 20:31:01 1998
|
|
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|
|
From: "Hiroshi Inoue" <Inoue@tpf.co.jp>
|
|
To: "Jan Wieck" <jwieck@debis.com>,
|
|
"Bruce Momjian" <maillist@candle.pha.pa.us>
|
|
Subject: RE: [HACKERS] What about LIMIT in SELECT ?
|
|
Date: Fri, 16 Oct 1998 09:12:55 +0900
|
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|
|
|
|
> -----Original Message-----
|
|
> From: owner-pgsql-hackers@postgreSQL.org
|
|
> [mailto:owner-pgsql-hackers@postgreSQL.org]On Behalf Of Bruce Momjian
|
|
> Sent: Thursday, October 15, 1998 2:52 PM
|
|
> To: jwieck@debis.com
|
|
> Cc: lockhart@alumni.caltech.edu; jwieck@debis.com; eric@linux-hw.com;
|
|
> jeff@remapcorp.com; hackers@postgreSQL.org
|
|
> Subject: Re: [HACKERS] What about LIMIT in SELECT ?
|
|
>
|
|
>
|
|
> > > I have had more time to think about this. Basically, for pre-sorted
|
|
> > > data, our psort code is very fast, because it does not need to sort
|
|
> > > anything. It just moves the rows in and out of the sort memory. Yes,
|
|
> > > it could be removed in some cases, and probably should be,
|
|
> but it is not
|
|
> > > going to produce great speedups.
|
|
> >
|
|
> > And I got the time to hack around about this.
|
|
> >
|
|
> > I hacked in a little check into the planner, that compares
|
|
> > the sortClause against the key field list of an index scan
|
|
> > and just suppresses the sort node if it exactly matchs and
|
|
> > all sort operators are "<".
|
|
> >
|
|
> > I tested with a 10k row table where key is a text field. The
|
|
> > base query is a
|
|
> >
|
|
> > SELECT ... WHERE key > 'val' ORDER BY key;
|
|
> >
|
|
> > The used 'val' is always a key that is close to the first of
|
|
> > all keys in the table ('' on the first query and the last
|
|
> > selected value on subsequent ones).
|
|
>
|
|
> This is good stuff. I want to think about it for a day. Sounds very
|
|
> promising.
|
|
>
|
|
|
|
Did you see my contribution about this subject ?
|
|
I have already implemented above cases and used on trial for three
|
|
months or more.
|
|
It is good to be formally supported by PostgreSQL community.
|
|
|
|
And please remember that there are descending order cases.
|
|
(Moreover there are compound cases such as
|
|
SELECT * from ... order by key1 desc,key2 asc;
|
|
I didn't implement such cases.)
|
|
|
|
Thanks.
|
|
|
|
Hiroshi Inoue
|
|
Inoue@tpf.co.jp
|
|
|
|
|
|
From owner-pgsql-hackers@hub.org Fri Oct 16 04:01:07 1998
|
|
Received: from renoir.op.net (root@renoir.op.net [209.152.193.4])
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|
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Fri, 16 Oct 1998 01:34:33 -0400 (EDT)
|
|
From: Bruce Momjian <maillist@candle.pha.pa.us>
|
|
Message-Id: <199810160534.BAA29942@candle.pha.pa.us>
|
|
Subject: Re: [HACKERS] What about LIMIT in SELECT ?
|
|
In-Reply-To: <m0zTY6V-000EBRC@orion.SAPserv.Hamburg.dsh.de> from Jan Wieck at "Oct 14, 1998 11: 5: 7 pm"
|
|
To: jwieck@debis.com
|
|
Date: Fri, 16 Oct 1998 01:34:33 -0400 (EDT)
|
|
Cc: lockhart@alumni.caltech.edu, jwieck@debis.com, eric@linux-hw.com,
|
|
jeff@remapcorp.com, hackers@postgreSQL.org
|
|
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|
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|
|
|
|
OK, I have had my day of thinking, and will address this specific
|
|
posting first, because it is the most fundamental concerning the future
|
|
direction of the optimization.
|
|
|
|
>
|
|
> And I got the time to hack around about this.
|
|
>
|
|
> I hacked in a little check into the planner, that compares
|
|
> the sortClause against the key field list of an index scan
|
|
> and just suppresses the sort node if it exactly matchs and
|
|
> all sort operators are "<".
|
|
>
|
|
> I tested with a 10k row table where key is a text field. The
|
|
> base query is a
|
|
>
|
|
> SELECT ... WHERE key > 'val' ORDER BY key;
|
|
>
|
|
> The used 'val' is always a key that is close to the first of
|
|
> all keys in the table ('' on the first query and the last
|
|
> selected value on subsequent ones).
|
|
>
|
|
> Scenario 1 (S1) uses exactly the above query but processes
|
|
> only the first 20 rows from the result buffer. Thus the
|
|
> frontend receives nearly the whole table.
|
|
|
|
OK.
|
|
|
|
>
|
|
> Scenario 2 (S2) uses a cursor and FETCH 20. But closes the
|
|
> cursor and creates a new one for the next selection (only
|
|
> with another 'val') as it would occur in a web application.
|
|
>
|
|
> If there is no index on key, the backend will allways do a
|
|
> Sort->SeqScan and due to the 'val' close to the lowest
|
|
> existing key nearly all tuples get scanned and put into the
|
|
> sort. S1 here runs about 10 seconds and S2 about 6 seconds.
|
|
> The speedup in S2 results from the reduced overhead of
|
|
> sending not wanted tuples into the frontend.
|
|
|
|
Makes sense. All rows are processed, but not sent to client.
|
|
|
|
>
|
|
> Now with a btree index on key and an unpatched backend.
|
|
> Produced plan is always a Sort->IndexScan. S1 needs 16
|
|
> seconds and S2 needs 12 seconds. Again nearly all data is put
|
|
> into the sort but this time over the index scan and that is
|
|
> slower.
|
|
|
|
VACUUM ANALYZE could affect this. Because it had no stats, it thought
|
|
index use would be faster, but in fact because 'val' was near the lowest
|
|
value, it as selecting 90% of the table, and would have been better with
|
|
a sequential scan. pg_statistics's low/hi values for a column could
|
|
have told that to the optimizer.
|
|
|
|
I know the good part of the posting is coming.
|
|
|
|
> Last with the btree index on key and the patched backend.
|
|
> This time the plan is a plain IndexScan because the ORDER BY
|
|
> clause exactly matches the sort order of the chosen index.
|
|
> S1 needs 13 seconds and S2 less than 0.2! This dramatic
|
|
> speedup comes from the fact, that this time the index scan is
|
|
> the toplevel executor node and the executor run is stopped
|
|
> after 20 tuples have been selected.
|
|
|
|
OK, seems like in the S1 case, the use of the psort/ORDER BY code on top
|
|
of the index was taking and extra 3 seconds, which is 23%. That is a
|
|
lot more than I thought for the psort code, and shows we could gain a
|
|
lot by removing unneeded sorts from queries that are already using
|
|
matching indexes.
|
|
|
|
Just for clarity, added to TODO. I think everyone is clear on this one,
|
|
and its magnitude is a surprise to me:
|
|
|
|
* Prevent psort() usage when query already using index matching ORDER BY
|
|
|
|
|
|
> Analysis of the above timings:
|
|
>
|
|
> If there is an ORDER BY clause, using an index scan is the
|
|
> clever way if the indexqual dramatically reduces the the
|
|
> amount of data selected and sorted. I think this is the
|
|
> normal case (who really selects nearly all rows from a 5M row
|
|
> table?). So choosing the index path is correct. This will
|
|
> hurt if someone really selects most of the rows and the index
|
|
> scan jumps over the disc. But here the programmer should use
|
|
> an unqualified query to perform a seqscan and do the
|
|
> qualification in the frontend application.
|
|
|
|
Fortunately, the optimizer already does the index selection for us, and
|
|
guesses pretty well if the index or sequential scan is better. Once we
|
|
implement the above removal of psort(), we will have to change the
|
|
timings because now you have to compare index scan against sequential
|
|
scan AND psort(), because in the index scan situation, you don't need
|
|
the psort(), assuming the ORDER BY matches the index exactly.
|
|
|
|
> The speedup for the cursor/fetch scenario is so impressive
|
|
> that I'll create a post 6.4 patch. I don't want it in 6.4
|
|
> because there is absolutely no query in the whole regression
|
|
> test, where it suppresses the sort node. So we have
|
|
> absolutely no check that it doesn't break anything.
|
|
>
|
|
> For a web application, that can use a unique key to select
|
|
> the next amount of rows, it will be a big win.
|
|
|
|
OK, I think the reason the regression test did not show your code being
|
|
used is important.
|
|
|
|
First, most of the tables are small in the regression test, so sequential
|
|
scans are faster. Second, most queries using indexes are either joins,
|
|
which do the entire table, or equality tests, like col = 3, where there
|
|
is no matching ORDER BY because all the col values are 3. Again, your
|
|
code can't help with these.
|
|
|
|
The only regression-type code that would use it would be a 'col > 3'
|
|
qualification with a col ORDER BY, and there aren't many of those.
|
|
|
|
However, if we think of the actual application you are addressing, it is
|
|
a major win. If we are going after only one row of the index, it is
|
|
fast. If we are going after the entire table, it is faster to
|
|
sequential scan and psort(). You big win is with the partial queries,
|
|
where you end up doing a full sequential scan or index scan, then and
|
|
ORDER BY, while you really only need a few rows from the query, and if
|
|
you deal directly with the index, you can prevent many rows from being
|
|
processed. It is the ability to skip processing those extra rows that
|
|
makes it a big win, not so much the removal of the ORDER BY, though that
|
|
helps too.
|
|
|
|
Your solution really is tailored for this 'partial' query application,
|
|
and I think it is a big need for certain applications that can't use
|
|
cursors, like web apps. Most other apps have long-time connections to
|
|
the database, and are better off with cursors.
|
|
|
|
I did profiling to improve startup time, because the database
|
|
requirements of web apps are different from normal db apps, and we have
|
|
to adjust to that.
|
|
|
|
So, to reiterate, full queries are not benefited as much from the new
|
|
code, because sequential scan/psort is faster, or because the index only
|
|
retrieves a small number of rows because the qualification of values is
|
|
very specific.
|
|
|
|
Those open-ended, give me the rows from 100 to 199 really need your
|
|
modifications.
|
|
|
|
OK, we have QUERY_LIMIT, and that allows us to throw any query at the
|
|
system, and it will return that many of the first rows for the ORDER BY.
|
|
No fancy stuff required. If we can get a matching index, we may be able
|
|
to remove the requirement of scanning all the row (with Jan's patch),
|
|
and that is a big win. If not, we at least prevent the rows from being
|
|
returned to the client.
|
|
|
|
However, there is the OFFSET issue. This is really a case where the
|
|
user wants to _restart_ the query where they left off. That is a
|
|
different problem. All of a sudden, we need to evaluate more of the
|
|
query, and return a segment from the middle of the result set.
|
|
|
|
I think we need to decide how to handle such a restart. Do we
|
|
re-evaluate the entire query, skipping all the rows up to OFFSET, and
|
|
return the number of rows they requested after OFFSET. I would think we
|
|
don't want to do that, do we. It would be much easier to code. If it
|
|
is a single table, skipping forward has to be done anyway, because we
|
|
can't just _jump_ to the 100th entry in the index, unless we pass some
|
|
_tid_ to the user, and expect them to pass that back to start the query.
|
|
I don't think we went to do that. It is ugly, and the row may have
|
|
moved since we started. So, for a single table, adding a QUERY_OFFSET
|
|
would do exactly what we need, with Jan's patches.
|
|
|
|
For a joined query, I think you will have to do the entire _join_ before
|
|
returning anything.
|
|
|
|
You can't just process all the joins up to the OFFSET location, and you
|
|
can't just jump to the 100th index location, because you don't know that
|
|
the 100th index location produced the 100th result just returned to the
|
|
user. You have to process the whole query, and because of the join and
|
|
not knowing which data row from each table is going to make which entry
|
|
in the final result. If you are really craft, and the ORDER BY table is
|
|
in the outer part of the join loop, you could start processing the table
|
|
that is part of the outer loop in _index_ order, because you know that
|
|
the rows processed in index order are going to produce the output in
|
|
result order. You then could process and throw away the results up to
|
|
offset, and generate the needed rows and stop.
|
|
|
|
The other way of doing it is to specify a query limit based on specific
|
|
index entries, so you say I want the query returned by the first 20
|
|
index entries matching the ORDER BY, or entries 100-199, and the query
|
|
is limited to using only those entries in the index. In that case,
|
|
though, in joins, you could return more or less rows in the result
|
|
depending on the other tables, and that may be unacceptable. However,
|
|
for this case, the advantage is that you don't need to process the rows
|
|
from 1 to 99 because you have been told the user only wants rows from
|
|
certain index slots. If the user requests rows 50000-50100, this would
|
|
be much faster because you don't have to process the 50000 rows before
|
|
returning any data. However, I question how often people grab stuff
|
|
from the center of large data sets. Seems the QUERY_OFFSET idea may be
|
|
easier for users.
|
|
|
|
I will be commenting on the rest of the optimization postings tomorrow.
|
|
|
|
--
|
|
Bruce Momjian | http://www.op.net/~candle
|
|
maillist@candle.pha.pa.us | (610) 853-3000
|
|
+ If your life is a hard drive, | 830 Blythe Avenue
|
|
+ Christ can be your backup. | Drexel Hill, Pennsylvania 19026
|
|
|
|
|
|
From Inoue@tpf.co.jp Fri Oct 16 03:31:02 1998
|
|
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for <maillist@candle.pha.pa.us>; Fri, 16 Oct 1998 03:31:00 -0400 (EDT)
|
|
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id QAA02680; Fri, 16 Oct 1998 16:04:09 +0900
|
|
From: "Hiroshi Inoue" <Inoue@tpf.co.jp>
|
|
To: "Bruce Momjian" <maillist@candle.pha.pa.us>
|
|
Cc: <jwieck@debis.com>
|
|
Subject: RE: [HACKERS] What about LIMIT in SELECT ?
|
|
Date: Fri, 16 Oct 1998 16:16:29 +0900
|
|
Message-ID: <000001bdf8d4$e4cdf520$2801007e@cadzone.tpf.co.jp>
|
|
MIME-Version: 1.0
|
|
Content-Type: text/plain;
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charset="iso-8859-1"
|
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Content-Transfer-Encoding: 7bit
|
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X-Priority: 3 (Normal)
|
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X-MSMail-Priority: Normal
|
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|
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In-Reply-To: <199810160621.CAA01030@candle.pha.pa.us>
|
|
Status: RO
|
|
|
|
Where's my contibution to hackers@potsgreSQL.org ?
|
|
I will resend it.
|
|
|
|
> -----Original Message-----
|
|
> From: Bruce Momjian [mailto:maillist@candle.pha.pa.us]
|
|
> Sent: Friday, October 16, 1998 3:22 PM
|
|
> To: Hiroshi Inoue
|
|
> Cc: jwieck@debis.com
|
|
> Subject: Re: [HACKERS] What about LIMIT in SELECT ?
|
|
>
|
|
>
|
|
> [Charset iso-8859-1 unsupported, filtering to ASCII...]
|
|
> > > > The used 'val' is always a key that is close to the first of
|
|
> > > > all keys in the table ('' on the first query and the last
|
|
> > > > selected value on subsequent ones).
|
|
> > >
|
|
> > > This is good stuff. I want to think about it for a day. Sounds very
|
|
> > > promising.
|
|
> > >
|
|
> >
|
|
> > Did you see my contribution about this subject ?
|
|
>
|
|
> I am sorry. I have not seen it, and I am confused how I could have
|
|
> missed it.
|
|
>
|
|
> > I have already implemented above cases and used on trial for three
|
|
> > months or more.
|
|
> > It is good to be formally supported by PostgreSQL community.
|
|
> >
|
|
> > And please remember that there are descending order cases.
|
|
> > (Moreover there are compound cases such as
|
|
> > SELECT * from ... order by key1 desc,key2 asc;
|
|
> > I didn't implement such cases.)
|
|
>
|
|
> Where is the discussion of this? I am confused. You have been using
|
|
> code for three months that does this?
|
|
>
|
|
|
|
Hi all.
|
|
I didn't follow all the posts about this thread.
|
|
So this post may be out of center.
|
|
|
|
I think current PostgreSQL lacks the concern to the response to get first
|
|
rows quickly.
|
|
For example,queries with ORDER BY clause necessarily include sort steps
|
|
and process all target rows to get first rows only.
|
|
So I modified my code for ORDER BY cases and use on trial.
|
|
I don't understand PostgreSQL sources,so my code is not complete.
|
|
|
|
I modified my code for the following 2 cases.
|
|
|
|
1.In many cases the following query uses index scan.
|
|
SELECT * from ... where key > ...; (where (key) is an index)
|
|
If so,we can omit sort steps from the access plan for the following
|
|
query.
|
|
SELECT * from ... where key > ... order by key;
|
|
|
|
Currently cursors without sort steps may be sensitive diffrent from
|
|
cursors with sort steps. But no one mind it.
|
|
|
|
2.In many cases the following query uses index scan same as case 1.
|
|
SELECT * from ... where key < ...;(where (key) is an index)
|
|
If so and if we scan the index backward,we can omit sort steps from
|
|
the access plan for the following query.
|
|
SELECT * from ... where key < ... order by key desc;
|
|
|
|
To achive this(backward scan),I used hidden(provided for the future ?)code
|
|
that is never executed and is not necessarily correct.
|
|
|
|
In the following cases I didn't modify my code to use index scan,
|
|
because I couldn't formulate how to tell PostgreSQL optimizer whether
|
|
the response to get first rows is needed or the throughput to process
|
|
sufficiently many target rows is needed.
|
|
|
|
3.The access plan made by current PostgreSQL optimizer for a query with
|
|
ORDER BY clause doesn't include index scan.
|
|
|
|
I thought the use of Tatsuo's QUERY_LIMIT to decide that the responce
|
|
is needed. It is sufficient but not necessary ?
|
|
In Oracle the hints FIRST_ROWS,ALL_ROWS are used.
|
|
|
|
Thanks.
|
|
|
|
Hiroshi Inoue
|
|
Inoue@tpf.co.jp
|
|
|
|
|
|
From wieck@sapserv.debis.de Fri Oct 16 05:01:03 1998
|
|
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|
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Message-Id: <m0zU57w-000EBQC@orion.SAPserv.Hamburg.dsh.de>
|
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From: jwieck@debis.com (Jan Wieck)
|
|
Subject: Re: [HACKERS] What about LIMIT in SELECT ?
|
|
To: Inoue@tpf.co.jp (Hiroshi Inoue)
|
|
Date: Fri, 16 Oct 1998 10:20:47 +0200 (MET DST)
|
|
Cc: maillist@candle.pha.pa.us, jwieck@debis.com
|
|
Reply-To: jwieck@debis.com (Jan Wieck)
|
|
In-Reply-To: <000001bdf8d4$e4cdf520$2801007e@cadzone.tpf.co.jp> from "Hiroshi Inoue" at Oct 16, 98 04:16:29 pm
|
|
X-Mailer: ELM [version 2.4 PL25]
|
|
Content-Type: text
|
|
Status: RO
|
|
|
|
Hiroshi Inoue wrote:
|
|
|
|
> In the following cases I didn't modify my code to use index scan,
|
|
> because I couldn't formulate how to tell PostgreSQL optimizer whether
|
|
> the response to get first rows is needed or the throughput to process
|
|
> sufficiently many target rows is needed.
|
|
>
|
|
> 3.The access plan made by current PostgreSQL optimizer for a query with
|
|
> ORDER BY clause doesn't include index scan.
|
|
>
|
|
> I thought the use of Tatsuo's QUERY_LIMIT to decide that the responce
|
|
> is needed. It is sufficient but not necessary ?
|
|
> In Oracle the hints FIRST_ROWS,ALL_ROWS are used.
|
|
|
|
I still think that the QUERY LIMIT should be part of the
|
|
parse tree and not thrown in by a magic SET command. If
|
|
rewriting or function calls turn the one query sent to the
|
|
backend into multiple queries processed internal, how should
|
|
this QUERY LIMIT variable know to which of all the queries it
|
|
has to be applied? It can really break functions and rewrite
|
|
rules if this variable is used on all queries while it is
|
|
set.
|
|
|
|
For your case 3 I think, if there is a QUERY LIMIT in the
|
|
parse tree, the (future) optimizer definitely knows that not
|
|
all rows will get processed even if there is no qualification
|
|
given. So if there is an index, that matches the ORDER BY
|
|
clause and it is no a join and the (future) executor handles
|
|
OFFSET in single table index scans fast, it could choose an
|
|
index scan for this query too.
|
|
|
|
|
|
Jan
|
|
|
|
--
|
|
|
|
#======================================================================#
|
|
# It's easier to get forgiveness for being wrong than for being right. #
|
|
# Let's break this rule - forgive me. #
|
|
#======================================== jwieck@debis.com (Jan Wieck) #
|
|
|
|
|
|
|
|
From owner-pgsql-hackers@hub.org Fri Oct 16 12:02:27 1998
|
|
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|
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|
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|
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|
|
Message-Id: <m0zUBum-000EBQC@orion.SAPserv.Hamburg.dsh.de>
|
|
From: jwieck@debis.com (Jan Wieck)
|
|
Subject: [HACKERS] SELECT ... LIMIT (trial implementation)
|
|
To: pgsql-hackers@postgreSQL.org (PostgreSQL HACKERS)
|
|
Date: Fri, 16 Oct 1998 17:35:39 +0200 (MET DST)
|
|
Reply-To: jwieck@debis.com (Jan Wieck)
|
|
X-Mailer: ELM [version 2.4 PL25]
|
|
Content-Type: text
|
|
Sender: owner-pgsql-hackers@postgreSQL.org
|
|
Precedence: bulk
|
|
Status: ROr
|
|
|
|
Here we go,
|
|
|
|
this is up to now only for discussion, do not apply to CVS!
|
|
|
|
Those involved into the LIMIT discussion please comment.
|
|
|
|
Here is what I had in mind for the SELECT ... LIMIT. It adds
|
|
|
|
SELECT ... [LIMIT count [, offset]]
|
|
|
|
to the parser and arranges that these values are passed down
|
|
to the executor.
|
|
|
|
It is a clean implementation of LIMIT (regression tested) and
|
|
the open items on it are to enable parameters and handle it
|
|
in SQL functions and SPI stuff (currently ignored in both).
|
|
Optimizing the executor would require the other sort node
|
|
stuff discussion first to come to a conclusion. For now it
|
|
skips final result rows - but that's already one step forward
|
|
since it reduces the rows sent to the frontend to exactly
|
|
that what LIMIT requested.
|
|
|
|
I've seen the queryLimit by SET variable stuff and that
|
|
really can break rewrite rules, triggers or functions. This
|
|
is because the query limit will be inherited by any query
|
|
(inserts, updates, deletes too) done by them. Have a rule for
|
|
constraint deletes of referencing tuples
|
|
|
|
CREATE RULE del_table1 AS ON DELETE TO table1 DO
|
|
DELETE FROM table2 WHERE ref = OLD.key;
|
|
|
|
If the user now sets the query limit to 1 via SET and deletes
|
|
a row from table1, only the first found record in table2 will
|
|
be constraint deleted, not all of them.
|
|
|
|
This is a feature where users can get around rules that
|
|
ensure data integrity.
|
|
|
|
|
|
Jan
|
|
|
|
--
|
|
|
|
#======================================================================#
|
|
# It's easier to get forgiveness for being wrong than for being right. #
|
|
# Let's break this rule - forgive me. #
|
|
#======================================== jwieck@debis.com (Jan Wieck) #
|
|
|
|
|
|
begin 644 opt_limit.diff.gz
|
|
M'XL(`$]=)S8"`^4\:W?B1K*?R:_H82=98&1;$F^<>`^+F1DV&!S`N<DGCBP:
|
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M6SM"(I*PQSOQ?[]5_9!:(`$S<1Y[+V<&I.[JZJ[NZGIUM1?.<DE.[("$@7WJ
|
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M!\[=V:UE?Z#>XLSV5RO+6X3RX=1&F#W57U4JE6/0%-X&#AG;$3$:Q#`Z]6JG
|
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MVB)&N]WZZN3DY$`?J;9FI][HU&J\;27]88.IMC6H9J^(&E_K!)Y.OB+D;XYG
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MNYL%)<5-Y+CAV<K^&)W>%S-JUGX066YV7?@4VI9]3['VC5(;1H'CW?$V\.^L
|
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MPKI5/U!**H7"-4/>_TCM3>0'[ZFUOJ(K/W@B8;19+C.I,G1#,_1&0I>AFU#0
|
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MDI05'"\J%`I+:D6;@)YCR0\;&CQ=TM"&/G^1SZR&]];SO8A^C(C-?\^!E@*4
|
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MA8#'=5:VO_&B<TY)(9N4`M`26IX3/1&8#?M#F#URHZH91DL9N5'7C&HM'OGS
|
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MGD[>L$YZ`9!%B85##2/B^3#;R\!?D>B>DCOG@7J$#9<\6.Z&\D8YN,[P9T57
|
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M(8U*WT@R-:)K)'3^0_UE29:5RVQ"Y.MI]+2FA<)W9#9G<Y2N9.-B$-^1P6A6
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M&P\N,P!<ZD&]Z`?6JU;.`&(D`%CI$E9R51;+L`/FA-[&=0'N;7<X[6<`W#X!
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M)ASOY*:?V1YF8$]S!U@\3`$@3#X?W-&(K0;?-\GJB'?/6E$.F8/@+)MWF@W-
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M:)F<=P`N=^/`?*68NHS0`OP=C1+($A]0F7'V*U*0N"8;KQ1O$HW$+:<1<)YL
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MI!&QOS3.;V6Y/YPE*2THL.9WWY&1[]$R;$68JZOQCWTD#<>R7@:4)EU`4[87
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MVK"+V\DN_NL06!KA+JN41S?#8?(6;YG?1OHB5P%1,5SV<&4YWI8&RJC/5D$9
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M@,?KH$.-&QU#[]1;^4JH4=,:[43DP6M3EXL<PHP[-GGPG07I>XMKU_)*^$4J
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M:_C62)\M":E0!*1LHD63V6;MTIEUZ]*IZT>DPM>6,@SI5K#`"4:V"%P=0(D5
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MA'0&"Z*1WFHQ`YE%_#4-`+\/D&\0$D03\9=+$!"LPU`@P&)OL[JE@2@F4]OR
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M+IV`VMB8+.23@&<$EBIK4(K1<N/995(JJ]3P"0`2)A04)WV@I6WZ0OC62!8>
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M+5M<-$#5R'E'5;LC;#[WP[`@%V\/#;:6NK,275M1-MGVFN`,QAL,7_A6`O2?
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M<,K$>A0*\8(D>KR``XG73@@/8"LCX:N_-KE<@(#XX)RE%'SY)&2K##"4FJJA
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MU`01VVS'(G:;M("&&Y=9.F#],(OS$L49RC16B.Q7*)0J6.!X;$3(@4QG,J.+
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M$P026D_*N#G"BJ1QL_,YWH)J`TEME:1V33/K"4E\PD\N:#A?![Y-0;<O9.=J
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MI0LJ'3<3&"D>6`?.8NPLV`#?9`^06U\@X;F-)76\(-A?LK?AX&HP([9K;4)A
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M>N4@8J87JHN8"<@KT!F@7\I8\XD)'V&`5FP.P684QL9^KJW`6D'=6JUC:-E3
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M4S<BS@H8=D5![2_($XV*>=TLZ-("3L[L8>/1CVN0SH""6<]HJY*O%]O]%362
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MNEUI;N-CV\ML'&0_KX$PE*LEU!*SHE'MY,C=MF;J]=C[$!^B&%6B(+:IU%+%
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MH:G5(NXNO]#`L^;<U%N::50376>"^C:;K1>@[,TN9>0%*<NDQH3!FTV%FE93
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M,]O5/X&:?X)K\YO)J<+H:Z827-.K6E5OORPY>@IF/.KS_?+2:],`JZJA6E7-
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M>DMK-FH*,8=]*%[\6QTI7OP%WE0F8<V:J35K"M.U#%UKF<HJ?>(HN>5+N"Y,
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M;\V4",Y1T*BA81U`A#^21]3-J#<BZCX1[CY3'@#".02CFH0?G+5L)GJ.&/D$
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|
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MN.!)NJ%L!KC7?A@Z8.Z3TF*#`5J`7="/)(3I+DNP$_(ORQ,O><2>;5D_?/'(
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MA51+0M6?G*C50G=BC-7Q-CPP&T<\,V?VB-@(KC^R1I@7'%$`#D1'%,@O"(_D
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MM:YV=*.CF_GQ$5/70;4VI&K%R1`J&<V=87<*ULMX.OOAIC^<]\975]W198F&
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M093`!)?68I1BX_QYH\P.QC$3-F?X1W!1N';R^(=5'>`<!I/!,^T#/+/;#KBE
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MU3';^=S2!%'=3(EJ5M",)=JM[[NP-4,921IXD3^A+I/%L%1+RPWYUK/OK8!%
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MPO1Z,&<&[7Q\?3/Z?C3^'\8K7%*\(?*3?402?RK\YXCCDBA]7J)@V(O_3'D[
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|
|
M'\#P)O$9238H.XJ1E(KCF#RDZ#$?A90?T&R!RH`\DQ\L(H\B@D?DF2)>!Q1]
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M/[8O1'1><"!C>SSK7()?Q_D1A-;-#%AR.NO.IMD,7@,&KQN)AZ2P\_C[>>]F
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M,AU/$D;./XX0`H_)R;?HUD7I4X8Y8K0W04#1`U:#7!FAKW,Y#?$>Q:GH75W.
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M3ZCDMRV-G=IL9;$#MJLO:GJVOMC?%/2,V:G6\U6&46^V-*/>4CQ)6:0LK$<?
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ML9^3BXT'T]9CH228Y(BNUG/7$0%@(8,+N%H@I]9/)12F&A&--1[1&/-@V?EA
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MR)Y8:KY=!6\)D%B;'UH8?Q/EKTM2N6]9$JC/796<EK`H>J>N[['ZZFW-;"C)
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M&;P@<>ZM]1IZF;(\BH&W]$&0!1J/K9U<W%OA=',[=+P/(1A8Q2C8T"+85D6F
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MW8O\:"D'`\"I*USDL'.@`Y>*P^PP`E_+7(3*JA,19<I"N,,<^Q$RYCB(KQ=+
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MB\\R_?CJ@76PR.<=I78?\RA@G\L]>4V!?8Q.K;IG3[/C/363!`N:B<<>^=`-
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M=Z6R"7<AU:[4VMVNWGQ!5YR!<GKJB8!R1D>)*$I:'2&-6"@D.+/`.7_Z#]WB
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MBCHBA@/Z]E6IE)2#'D^B7&50VBRC`O->1-!:!%V2J$L46%ZX](-5@J2T%B9#
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MNPNLU>E3%D?PFKWLQD$R>,W<RVL9S>H=L[HW(Q&,Y+KB!.*KL9N1:%O`+_[=
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M&?PBUV2G'N+)QW:-9:,=>/;1LJ/MC$2)<WTW1P\J3DT45O[5S7`V^.?/LWX*
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MW^H6X1_15<8&1R1:%`JPQ-&<'\6!V0LOMT_,@-)XL&W.#IQ"^<9KD$K^R%"@
|
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MJ12C8"\<S%]'<RL(K*?Y+;#>(D1S*MPJ8@CHQW4@VEA1%``@<.,\LH([&HGR
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MK0*3GVW`5"A]P1#CT"NY"_S-.A[5#/CHC@9O07EU@[N0S^77S#?]%N7E10'U
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MVIS+T:0*HQ/4\BX*L/?FT(62O&$DMNC_RRGDK;%-R&3"G,F8+Y[8[%,\3+%K
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M;F5/Z(8BY@4Z!]QTZ(E&]OW\WG^<KRSOB:O[U%#4D<YE!"7!@M-P41BOHRG]
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M90C/20U,$G7CNKY+5WDGCV:CJ9G-:K*_F(<_O];(V_ZL]QY^AN/N#'[0J82O
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M_N#="!XFXROX1ON`-7HWZ8X`Z-UD?`,MWW=_'(S>P>_X9@*8&,0`6@U&HSX6
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MP,.T/YH.9H,?^_QE,L/?67_R8W?(GL;P/>5+]J\QMOV^_[-&AMW1NYON.V@T
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M['<O61_#_EMH.QQ\CX7C7E<,Z*K+!G\U&-W,9X]'L/3Z,NE?R0'34G0W&
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M(^P1GFXF[*'WO@N$COH_`=;1&/_C`Q#*VMY<]2>#'F\]?JN1\0C_#V%HXVO$
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M!;\3_'_9QQ_HFM'/#Q<-F.<DCOA?/<]X:O+7G>X<?]#`1*9&RB.L@TNH*X*Q
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M0(15H8@W\GA/`RI>!)0J:,B]]0#^51J`V?420!&WW)@A&5*HH-AM!=5J07M\
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M97V@S#M+*J0%4RAXS(WX98,>Q&LSYSBUH>.IO:Z>#\,;%)EFZDC50^<7Z8F=
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MDM>MK9X4A^5U6ZU#.I,J0Y?&'[-@7QL&RX49#,NR^%-\%.OMN"?1?4G7`(D1
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MFZ$)5.Q:`)"Q!?0L'YBE>+@C'I'/ZR%5^RQ)??T:C5<14?/D#/#JO.G'_(ZF
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MKL8CF@;HAJ8:H?^5=*<]>:Q<^$18/\5OB^?D6=1?]C,`+A2`LTK_ZGKV<^4L
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M"\M91>315,X(GR?A]VVS8Z?`ST5WU0_YN_9WDJF59$\N#SJ4Y"\L."Q1K0Q?
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M9OE<]/LKR>O@$"869=["!5XIHUJXHJ(Y@)^GR=SMK5,8L`BW=)OX2O/CF/3&
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M8V4QFWDB-2KC'H92FW,)0X'8NH'QVM@&R+A[H=3N7+Q(M=R^=9&JW+YRD<77
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MPO'BD\PRO$9^>J9R,KW`&1.Y5]SBVYOK)?>-N,ATV!?[0)\>_6`19D<`DMJ]
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M/ED"]ME^64[3.K3KF'M"D@9L>,-,3C`^%9E]740]?-G_Z5F3A:!OG"ADY>]!
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M_\VF295'@V*LWZ'XA!?#L**BU/`)=$B]T&&I:2E30`&(J+7@E3-0]$D%K"*P
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M5C$Q%I0JGQ>/GS5QQXJ3)<782Y!U</QO]M/]&\G*7#VSI1E5-<;/"FH*W>`@
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M+$!S%F.K26)WZ3(J<A,J+G(^(%5H3TERV(XI"NLJ@0-B/%8*M(SB8I\1"";C
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M95)D,]*850:%^?LHH(^P$E3^7M*EXVW'TW)@LO=4#G#&SFID[ZQC$$#K5J>^
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MYQRF:IA:U5`L'%9@*AEP]]1"J\T/:8D^@"0"+\]-L@5%FHQ(P1$:RO'(@T,?
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MB<.%6+A98[2-+G82==BQ5]JZ$*F_Y-=?B5K;V\D+WA*D:K9QNE<YG+`8AVQQ
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MQ(2/^/3TE*4_+47^$I[!!QN7DM4FY)FJ()\7!'-%$`D+_8BV_'PVY"E?)9E0
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|
M.T<0&!"V^!IW+I\U__;?)Q<P=2SBN"]X%MG^^FS-:-]BKU1--E.E0#)8J9G-
|
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M2OG-:AW=[%0;>X)GNE:+\X24R-;V+6$9VA(G(1B](A6>"3&6YZ*8:,QR\N("
|
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M,!5@LEZEKB1=\X/5^(Y+YFT7R9S9]WP_^]X-BPLR2G?C@G\RI8>O[KSL5&2G
|
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MBX%3:!B_Q\4N]>3LU9%K+^\J95Y*PEN<KN7Q8G@0"=J"@M_AKM874'#\=:PC
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M2<P4_55=JU;CO8MIEL2RHPT3@\'&B]-#3T\/7`T^+L-B<C.2^7SB.GEH/5"0
|
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MSDL_9-9OWUN(&UY"MMZL%]!<E+&SV"2#E^Q<F]*RDB_$/5Y)JW(C^O>G55F]
|
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MG0R2/XSZS)5O5K5JLYF$+YD*FR/])7['E3%3%)_Y,'>#!0<PYK7#PFFI^\QG
|
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M7/01VQ$OU8?2,&4Y[):KI_"[^E8(\/1=8GPXO6>Z<4]]6O?N`=S5P/4M8^[8
|
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MQF9'KW6,/:>EK:K64F_6`@]$/KK:(<\MC%.!T1Q2+F=+*44_@IWO\8NE3!I)
|
|
M+I]&5A`==:.4Z2\5S\Y5Z!>XC'N>C#6^H(R(8?L<.\@8`=[*9P-E6%BT(H!9
|
|
MB<(25]K@&[@TT$B<J@KVFZ:T8OGQ924M[X>;_N3G.3-%>:8:6Y1$I_S?6I1C
|
|
M[([_BJ7*%PX\(X8)%O:X)1MVJ[-%PRY<AF1H94N&`VVKG6J]4]V3RM_0M49=
|
|
M^5,'\-I44RCP#(Q9"DJ4^ASU$WL/B1504%_>!W""-MZ"!EQ5!O3!\3>A>J6G
|
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MPATVX=\A+S"T:F(#HOT;W@]-7S")?)XAD]62YS,4\EN*K!BV7X1F93$+<.>P
|
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M&G6-!Z/F.C4F]M8**7JR/(T0&V$)D;XMP>*\OWK2J+:UAOHWC!HU`PJ2-+DX
|
|
MBSU),N$4*']QI62SQ(LRCM'F">%\B#Q7_A;<T>#IG*<&6X2_LHNFC+*R0/./
|
|
J5".V8K`1>&?LC3PZT;V_B8@X[<#CAC]SA9Y)<AHC_9+_!=<!%F+O2@``
|
|
`
|
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end
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From oleg@sai.msu.su Sun Oct 18 14:01:49 1998
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Received: from renoir.op.net (root@renoir.op.net [209.152.193.4])
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by candle.pha.pa.us (8.9.0/8.9.0) with ESMTP id OAA01739
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for <maillist@candle.pha.pa.us>; Sun, 18 Oct 1998 14:01:48 -0400 (EDT)
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|
Received: from ra.sai.msu.su (ra.sai.msu.su [158.250.29.2]) by renoir.op.net (o1/$ Revision: 1.18 $) with ESMTP id NAA23532 for <maillist@candle.pha.pa.us>; Sun, 18 Oct 1998 13:51:14 -0400 (EDT)
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Received: from ra (ra [158.250.29.2])
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by ra.sai.msu.su (8.9.1/8.9.1) with SMTP id UAA17832;
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Sun, 18 Oct 1998 20:45:25 +0300 (MSK)
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Date: Sun, 18 Oct 1998 21:45:24 +0400 (MSD)
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From: Oleg Bartunov <oleg@sai.msu.su>
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X-Sender: megera@ra
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To: Tom Lane <tgl@sss.pgh.pa.us>
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cc: Bruce Momjian <maillist@candle.pha.pa.us>, pgsql-hackers@postgreSQL.org,
|
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jwieck@debis.com
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Subject: Re: [HACKERS] SELECT ... LIMIT (trial implementation)
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In-Reply-To: <2292.908726689@sss.pgh.pa.us>
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Message-ID: <Pine.GSO.3.96.SK.981018213213.17519C-100000@ra>
|
|
Organization: Sternberg Astronomical Institute (Moscow University)
|
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MIME-Version: 1.0
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Content-Type: TEXT/PLAIN; charset=US-ASCII
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Status: RO
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On Sun, 18 Oct 1998, Tom Lane wrote:
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> Date: Sun, 18 Oct 1998 12:04:49 -0400
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> From: Tom Lane <tgl@sss.pgh.pa.us>
|
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> To: Bruce Momjian <maillist@candle.pha.pa.us>
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> Cc: pgsql-hackers@postgreSQL.org
|
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> Subject: Re: [HACKERS] SELECT ... LIMIT (trial implementation)
|
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>
|
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> Bruce Momjian <maillist@candle.pha.pa.us> writes:
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> > What if someone wants the rows from 500 to the end. Should we allow
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> > the syntax to be:
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> > SELECT ... [LIMIT count] [OFFSET offset]
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> > LIMIT and OFFSET are independent.
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>
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> I like that syntax the best, but remember we are not inventing in
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> a green field here. Isn't this a feature that already exists in
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> other DBMs? We should probably copy their syntax, unless it's
|
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> truly spectacularly awful...
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>
|
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> regards, tom lane
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>
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Mysql uses LIMIT [offset,] rows
|
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>From documentation:
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LIMIT takes one or two numeric arguments. A single argument
|
|
represents the maximum number of rows to return in a result. If two
|
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arguments are given the first argument is the offset to the first row to
|
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return, while the second is the maximum number of rows to return in the
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result.
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What would be nice if somehow total number of rows could be returned.
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This is often needed for altavista-like application.
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Of course, I can do
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select count(*) from sometable ... LIMIT offset, rows
|
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and then
|
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select ... from sometable ... LIMIT offset, rows
|
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but this seems not elegant solution.
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Regards,
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|
|
|
Oleg
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|
_____________________________________________________________
|
|
Oleg Bartunov, sci.researcher, hostmaster of AstroNet,
|
|
Sternberg Astronomical Institute, Moscow University (Russia)
|
|
Internet: oleg@sai.msu.su, http://www.sai.msu.su/~megera/
|
|
phone: +007(095)939-16-83, +007(095)939-23-83
|
|
|
|
|
|
From owner-pgsql-hackers@hub.org Sun Oct 18 14:31:12 1998
|
|
Received: from renoir.op.net (root@renoir.op.net [209.152.193.4])
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by candle.pha.pa.us (8.9.0/8.9.0) with ESMTP id OAA02288
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for <maillist@candle.pha.pa.us>; Sun, 18 Oct 1998 14:31:10 -0400 (EDT)
|
|
Received: from hub.org (majordom@hub.org [209.47.148.200]) by renoir.op.net (o1/$ Revision: 1.18 $) with ESMTP id OAA24844 for <maillist@candle.pha.pa.us>; Sun, 18 Oct 1998 14:15:35 -0400 (EDT)
|
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Received: from localhost (majordom@localhost)
|
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by hub.org (8.8.8/8.8.8) with SMTP id OAA26655;
|
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Sun, 18 Oct 1998 14:00:03 -0400 (EDT)
|
|
(envelope-from owner-pgsql-hackers@hub.org)
|
|
Received: by hub.org (TLB v0.10a (1.23 tibbs 1997/01/09 00:29:32)); Sun, 18 Oct 1998 13:58:57 +0000 (EDT)
|
|
Received: (from majordom@localhost)
|
|
by hub.org (8.8.8/8.8.8) id NAA26381
|
|
for pgsql-hackers-outgoing; Sun, 18 Oct 1998 13:58:55 -0400 (EDT)
|
|
(envelope-from owner-pgsql-hackers@postgreSQL.org)
|
|
X-Authentication-Warning: hub.org: majordom set sender to owner-pgsql-hackers@postgreSQL.org using -f
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Received: from ra.sai.msu.su (ra.sai.msu.su [158.250.29.2])
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by hub.org (8.8.8/8.8.8) with ESMTP id NAA26367
|
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for <pgsql-hackers@postgreSQL.org>; Sun, 18 Oct 1998 13:58:49 -0400 (EDT)
|
|
(envelope-from oleg@sai.msu.su)
|
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Received: from ra (ra [158.250.29.2])
|
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by ra.sai.msu.su (8.9.1/8.9.1) with SMTP id UAA18077;
|
|
Sun, 18 Oct 1998 20:58:41 +0300 (MSK)
|
|
Date: Sun, 18 Oct 1998 21:58:41 +0400 (MSD)
|
|
From: Oleg Bartunov <oleg@sai.msu.su>
|
|
X-Sender: megera@ra
|
|
To: Jan Wieck <jwieck@debis.com>
|
|
cc: PostgreSQL HACKERS <pgsql-hackers@postgreSQL.org>
|
|
Subject: Re: [HACKERS] SELECT ... LIMIT (trial implementation)
|
|
In-Reply-To: <m0zUBum-000EBQC@orion.SAPserv.Hamburg.dsh.de>
|
|
Message-ID: <Pine.GSO.3.96.SK.981018215259.17519D-100000@ra>
|
|
Organization: Sternberg Astronomical Institute (Moscow University)
|
|
MIME-Version: 1.0
|
|
Content-Type: TEXT/PLAIN; charset=US-ASCII
|
|
Sender: owner-pgsql-hackers@postgreSQL.org
|
|
Precedence: bulk
|
|
Status: RO
|
|
|
|
Jan,
|
|
|
|
I tested your patch on my Linux box and it works ok, except
|
|
aggregates functions doesn't work properly, for example
|
|
count(*) always produces 0
|
|
|
|
kdo=> select count(*) from work_flats limit 10,1000;
|
|
count
|
|
-----
|
|
(0 rows)
|
|
|
|
while
|
|
|
|
kdo=> select rooms from work_flats limit 10,1000;
|
|
rooms
|
|
-----
|
|
3
|
|
3
|
|
3
|
|
3
|
|
3
|
|
3
|
|
3
|
|
3
|
|
3
|
|
3
|
|
(10 rows)
|
|
|
|
|
|
Regards,
|
|
|
|
Oleg
|
|
_____________________________________________________________
|
|
Oleg Bartunov, sci.researcher, hostmaster of AstroNet,
|
|
Sternberg Astronomical Institute, Moscow University (Russia)
|
|
Internet: oleg@sai.msu.su, http://www.sai.msu.su/~megera/
|
|
phone: +007(095)939-16-83, +007(095)939-23-83
|
|
|
|
|
|
|
|
From wieck@sapserv.debis.de Sun Oct 18 15:17:53 1998
|
|
Received: from dsh.de (firewall-user@neptun.sns-felb.debis.de [53.122.101.2])
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for <maillist@candle.pha.pa.us>; Sun, 18 Oct 1998 15:17:49 -0400 (EDT)
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|
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id m0zUyWO-000EBPC; Sun, 18 Oct 98 21:29 MET DST
|
|
Message-Id: <m0zUyWO-000EBPC@orion.SAPserv.Hamburg.dsh.de>
|
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From: jwieck@debis.com (Jan Wieck)
|
|
Subject: Re: [HACKERS] SELECT ... LIMIT (trial implementation)
|
|
To: oleg@sai.msu.su (Oleg Bartunov)
|
|
Date: Sun, 18 Oct 1998 21:29:43 +0200 (MET DST)
|
|
Cc: tgl@sss.pgh.pa.us, maillist@candle.pha.pa.us, pgsql-hackers@postgreSQL.org,
|
|
jwieck@debis.com
|
|
Reply-To: jwieck@debis.com (Jan Wieck)
|
|
In-Reply-To: <Pine.GSO.3.96.SK.981018213213.17519C-100000@ra> from "Oleg Bartunov" at Oct 18, 98 09:45:24 pm
|
|
X-Mailer: ELM [version 2.4 PL25]
|
|
Content-Type: text
|
|
Status: RO
|
|
|
|
Oleg Bartunov wrote:
|
|
|
|
> On Sun, 18 Oct 1998, Tom Lane wrote:
|
|
>
|
|
> > Bruce Momjian <maillist@candle.pha.pa.us> writes:
|
|
> > > What if someone wants the rows from 500 to the end. Should we allow
|
|
> > > the syntax to be:
|
|
> > > SELECT ... [LIMIT count] [OFFSET offset]
|
|
> > > LIMIT and OFFSET are independent.
|
|
> >
|
|
> > I like that syntax the best, but remember we are not inventing in
|
|
> > a green field here. Isn't this a feature that already exists in
|
|
> > other DBMs? We should probably copy their syntax, unless it's
|
|
> > truly spectacularly awful...
|
|
> >
|
|
> > regards, tom lane
|
|
> >
|
|
>
|
|
> Mysql uses LIMIT [offset,] rows
|
|
> >From documentation:
|
|
>
|
|
> LIMIT takes one or two numeric arguments. A single argument
|
|
> represents the maximum number of rows to return in a result. If two
|
|
> arguments are given the first argument is the offset to the first row to
|
|
> return, while the second is the maximum number of rows to return in the
|
|
> result.
|
|
|
|
Simple change, just flip them in gram.y.
|
|
|
|
And for the 500 to end:
|
|
|
|
SELECT ... LIMIT 500, 0 (after flipped)
|
|
|
|
The 0 has the same meaning as ALL. And that could also be
|
|
added to the parser easily so one can say
|
|
|
|
SELECT ... LIMIT 500, ALL
|
|
|
|
too.
|
|
|
|
>
|
|
> What would be nice if somehow total number of rows could be returned.
|
|
> This is often needed for altavista-like application.
|
|
> Of course, I can do
|
|
> select count(*) from sometable ... LIMIT offset, rows
|
|
> and then
|
|
> select ... from sometable ... LIMIT offset, rows
|
|
> but this seems not elegant solution.
|
|
|
|
Absolutely makes no sense for me. As said in the other
|
|
posting, aggregates do the counting scan in a deeper level
|
|
and thus cannot get limited. So if you invoke an aggregate,
|
|
the whole scan is always done.
|
|
|
|
|
|
Jan
|
|
|
|
--
|
|
|
|
#======================================================================#
|
|
# It's easier to get forgiveness for being wrong than for being right. #
|
|
# Let's break this rule - forgive me. #
|
|
#======================================== jwieck@debis.com (Jan Wieck) #
|
|
|
|
|
|
|
|
From owner-pgsql-hackers@hub.org Sun Oct 18 19:08:47 1998
|
|
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|
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|
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Message-Id: <m0zUz52-000EBPC@orion.SAPserv.Hamburg.dsh.de>
|
|
From: jwieck@debis.com (Jan Wieck)
|
|
Subject: Re: [HACKERS] SELECT ... LIMIT (trial implementation)
|
|
To: terry@terrym.com (Terry Mackintosh)
|
|
Date: Sun, 18 Oct 1998 22:05:31 +0200 (MET DST)
|
|
Cc: hackers@postgreSQL.org
|
|
Reply-To: jwieck@debis.com (Jan Wieck)
|
|
In-Reply-To: <Pine.LNX.3.95.981018155322.29282B-100000@terry1.acun.com> from "Terry Mackintosh" at Oct 18, 98 03:58:57 pm
|
|
X-Mailer: ELM [version 2.4 PL25]
|
|
Content-Type: text
|
|
Sender: owner-pgsql-hackers@postgreSQL.org
|
|
Precedence: bulk
|
|
Status: RO
|
|
|
|
>
|
|
> On Sun, 18 Oct 1998, Tom Lane wrote:
|
|
>
|
|
> > Bruce Momjian <maillist@candle.pha.pa.us> writes:
|
|
> > > What if someone wants the rows from 500 to the end. Should we allow
|
|
> > > the syntax to be:
|
|
> > > SELECT ... [LIMIT count] [OFFSET offset]
|
|
> > > LIMIT and OFFSET are independent.
|
|
> >
|
|
> > I like that syntax the best, but remember we are not inventing in
|
|
> > a green field here. Isn't this a feature that already exists in
|
|
> > other DBMs? We should probably copy their syntax, unless it's
|
|
> > truly spectacularly awful...
|
|
> >
|
|
> > regards, tom lane
|
|
>
|
|
> None that I have used (VFP, M$ SQL Server) that had 'LIMIT', had 'OFFSET'.
|
|
> So it would seem that the very idea of OFFSET is to break with what others
|
|
> are doing.
|
|
>
|
|
> I too like the above syntax.
|
|
> Why mimic, when you can do better? Go for it!
|
|
>
|
|
|
|
We have a powerful parser. So we can provide
|
|
|
|
... [ LIMIT { rows | ALL } ] [ OFFSET skip ]
|
|
|
|
or
|
|
|
|
... [ LIMIT [ skip , ] { rows | ALL } ]
|
|
|
|
at the same time.
|
|
|
|
|
|
Jan
|
|
|
|
--
|
|
|
|
#======================================================================#
|
|
# It's easier to get forgiveness for being wrong than for being right. #
|
|
# Let's break this rule - forgive me. #
|
|
#======================================== jwieck@debis.com (Jan Wieck) #
|
|
|
|
|
|
|
|
|
|
From owner-pgsql-hackers@hub.org Sun Oct 18 19:08:39 1998
|
|
Received: from renoir.op.net (root@renoir.op.net [209.152.193.4])
|
|
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|
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for <maillist@candle.pha.pa.us>; Sun, 18 Oct 1998 19:08:37 -0400 (EDT)
|
|
Received: from hub.org (majordom@hub.org [209.47.148.200]) by renoir.op.net (o1/$ Revision: 1.18 $) with ESMTP id QAA03555 for <maillist@candle.pha.pa.us>; Sun, 18 Oct 1998 16:56:03 -0400 (EDT)
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|
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|
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|
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Received: by orion.SAPserv.Hamburg.dsh.de
|
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for jwieck@debis.com
|
|
id m0zUzgV-000EBPC; Sun, 18 Oct 98 22:44 MET DST
|
|
Message-Id: <m0zUzgV-000EBPC@orion.SAPserv.Hamburg.dsh.de>
|
|
From: jwieck@debis.com (Jan Wieck)
|
|
Subject: Re: [HACKERS] SELECT ... LIMIT (trial implementation)
|
|
To: jwieck@debis.com
|
|
Date: Sun, 18 Oct 1998 22:44:15 +0200 (MET DST)
|
|
Cc: terry@terrym.com, hackers@postgreSQL.org
|
|
Reply-To: jwieck@debis.com (Jan Wieck)
|
|
In-Reply-To: <m0zUz52-000EBPC@orion.SAPserv.Hamburg.dsh.de> from "Jan Wieck" at Oct 18, 98 10:05:31 pm
|
|
X-Mailer: ELM [version 2.4 PL25]
|
|
Content-Type: text
|
|
Sender: owner-pgsql-hackers@postgreSQL.org
|
|
Precedence: bulk
|
|
Status: RO
|
|
|
|
> We have a powerful parser. So we can provide
|
|
> [...]
|
|
|
|
This version now accepts all of the following
|
|
|
|
... [ LIMIT rows ] [ OFFSET skip ]
|
|
... [ OFFSET skip ] [ LIMIT rows ]
|
|
... [ LIMIT [ skip , ] rows ]
|
|
|
|
rows can be a positive integer constant greater that 0, a $n
|
|
parameter (in SPI_prepare()) or the keyword ALL. 0 isn't
|
|
accepted as constant to force ALL in that case making clear
|
|
that this is wanted. In the parameter version the integer
|
|
value 0 still is used to mean ALL.
|
|
|
|
skip can be a positive integer constant greater or equal to 0
|
|
or a $n parameter for SPI_prepare.
|
|
|
|
If any of these syntaxes is used in SPI_prepare()'d plans,
|
|
the given tcount argument for SPI_execp() is ignored and the
|
|
plan or parameter values are used.
|
|
|
|
Anyone happy now?
|
|
|
|
|
|
Jan
|
|
|
|
--
|
|
|
|
#======================================================================#
|
|
# It's easier to get forgiveness for being wrong than for being right. #
|
|
# Let's break this rule - forgive me. #
|
|
#======================================== jwieck@debis.com (Jan Wieck) #
|
|
|
|
begin 644 opt_limit.diff.gz
|
|
M'XL(")%0*C8"`V]P=%]L:6UI="YD:69F`.4\:W?;-K*?U5^!:-.NY-"V*-EZ
|
|
MN?$>5:83;67)U2-MSSWWZ-`29/-&(E62BN--_=_OS``@08F4E4>;[JY/&Y'`
|
|
M8(`9#&8&@P%GSGS.#J<^"_SID><[M\<W]O0M=V?'4V^YM-U9H!Z.I@BSH_J;
|
|
M@X.#?=#D+GV']:<A,ZO,-)NGE6:ESLQ&H_[-X>'A$WTDVI:;I]7FR8EH>Y#\
|
|
MH\%4&@94TRNBQM=3!D^'WS#V-\>=+M8SSO+KT%D$Q\OI^_#H+I]2L_+\T%ZD
|
|
MUP4/P=2>WG&L?:'5!J'ON+>B#?QW?$#=ZG]0R@YRN6M";KWGTW7H^:^YO;KB
|
|
M2\]_8$&XGL]3J3)+IF&6JC%=9JD,!75%6<YQPUPN-^=VN/;Y&9;\M.;^PP4/
|
|
MIM#G;^J9:D1O;<\-^?N03<7O&="2@[(`\"R<Y=1;N^&9H"273DH.:`ELUPD?
|
|
M&'!C^C9('[E9,4RSKHW</#7,RDDT\L<=G;R@3MH^D,69C4,-0N9ZP.VY[RU9
|
|
M>,?9K?..NXR&R][9BS47C3)P'>//DB\#'A:^4V0:K&2PP/D7]^8%558L$D/4
|
|
MZU'XL.*YW$LVFA"/DI4T+H)XR3J]T4F_<Y$"L.`NU,M^8+Y.BBE`1`*`%2Y@
|
|
M)I=%.0U;8$[@KA<+@+ML=8=6"L#-`V#"\0[&5FI[X,".Y@Z(>)``0)AL.;CE
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|
M(<V&6#?Q[,AWUUYR`9F!X#A==FI5PZR7A>P`7.;"`7XEA+J(T!+\%0]CR((8
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|
M4)$D^QG+*5R#M5N(%HG!HI;#$"1/-3*87%^&D+>B6A_.G!5F'$3SY4O6\UQ>
|
|
MA*4(O+KJO[&0-!S+:NYS'G<!36DM-&`5-^)5_-<AL-##5790[(V[W?@M6C*?
|
|
M1_HLTP!Q.5QZN+(==\,"I=2GFZ`4P/UMT!.-RZ5FZ;1I-K*-4/7$J#9BE0>O
|
|
MM9*:Y``X[DS9.\^9,<N=72]LMX#_L(,5_&LPBZ:$'7`$Y,1HV62T7BWXR+Y9
|
|
M\.'""]F!F%M.&)*M8()CC#0)PAQ`B>T'?`038K#V<C8"G<6\%?<!OP>0+Q`2
|
|
M5!/SYG-0$-1A(!%@L;M>WG!?%K/AU'8O')]/L3&;J2<)3P06#E9@%,/YVIT6
|
|
M6:&H4R,8`"0,.!A._HX7-ND+X%^#I>$QTM5%%4R-XCN:VBUE\[%_A`6E>'-H
|
|
ML+3TE17;V@-MD6W."7(P6F#X(I82H/^`+)/SD<M%$Q+;\1P.))H[J3Q`K,Q8
|
|
MKO[:Y`H%`NI#2)96\.E,2#<9X"C5=$>I!BJVUHA4["9I/@_6"_)TP/LAC_,"
|
|
MU1GJ-"I$\<OE"@=8X+@T(I1`LIGD=`F"0$.7XC+ACE"1<FZV_O;WH!I`4D,G
|
|
MJ7%BE.LQ28+AA^<\F*Q\;\K!ML]4YWKE`DPZ+B9P4ESP#IQ9WYG1`%^D#U!X
|
|
M7Z#AA8^E;+PDV)O36[=SU1FQZ<)>!]+URD!$KA>:BT@(V#.P&6!?BECS@92/
|
|
M=$`/I@*".)J[MGU["86KK<*N$X0==^[E5O36$54T!8YR6G+!O1-.[U@!_<:1
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MV;*CU>X2'@WL8Z4GJRF(C]D\V>&,BY06/7L2"VIQ?"GTH!M8OXM@!8\%L6?Y
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MO?B$KH0`9?34ECY$2D>Q*HI;[:&-R)[YQ[9K+Q[^Q3<D:K,R7:`VH5+DR4R7
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M/++8N!?!:%,6(>9ZRM"'#$[$,<+0M]U@[OG+&$EA)1V&3,3JC$E@V12@C0'I
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M291'GV23N*^19!.5Z612X$$DX\?I_IOU=),N(2)43)O<+>[N&&9RX>GK_#-6
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M,H`S8Y;C_(@/>8K?Y>4&Z=%0A>!+.V&0CW=,<97+_7P4*X#B0U$,PPKS*EH0
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M0P?<%68BGP@K:``AMV?Y:$,65X3<!P'-QX$'K<H3Q?U'0WZW1)"E7+0O0=:3
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MXW^QF^[/)"MU]LIUPZSH.014<*+1O8!>85>0CR(P"ON"S\.\",=$1<Y;I`IC
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M6GD5SE&XW?42)F^:C\([JL*;0UG_4I$07804/EH$Y<QPWG$O'14M</SM\0"V
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MRS$<$MI'(K.5@,_O08RX^KW@<\?=/&S,@$E7"!G`*6JAFJX6]D$`K>O-TQU)
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M*A6S;%3,Q&66<O(RRQVW<3OM!;S`WW$WG/@RMS1*%<H=JVQZZ6T[+GOG\'OF
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MB`3J8+W"HT@^V\JYIYR@W=G<GY3)G>A5#2?07-1C$=B#$1\='=%-AKF\BH!Y
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MF?YZP2/?%P\X9@S3F1$)G8O)MB)U+1"W-PKJ;MP$06!`V.);%#_!->_F_P[/
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M@75T'+OK9#&<>JOC%=&^(5Z)FG2A2H"DB%(M792RFYTT2^7=)XLEXR1*9=>.
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M_38_&Z;._62:"![ML0.1\]]726-X9Y"NUT0%8,Z!6<\2WRBY%EEGT4<O4C]_
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MH80S_<-?'_TA#CHT)4JW#TV_,J5/?\OCR[(B_4;#J5$VS3_B2R]Z6M&S/>=>
|
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M?;PD]2LE^%FGA>V*8GB0=RTE!7_`QUL^@8+]O\^R)XFIJK]2,BJ5:.UBKC:S
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MI^&:U*"_=J.;7D='3WPK;+_DT\&XIZZ<R._+!39%$N9>0)>F+7<F/_DB=>MX
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M\0$7F;`)TE\0'[V*LON+4?ZIB-KB&<66"">U[J/@N.PC\B.^5!]:PXT$YLUR
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M/45QV]Y*!9[\N!@^'-V1;=Q1G[2].P"W+?#IAC.W;^-RLW32-'>DDM4K1EW_
|
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M?1OM"WR=ZRP>:_3%,D0,RV??048(\#-]-%#"0C$;'[@2!@5AM&%CL^"^P:+;
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M5."_&5HKNDY4U&XL_#2V!K].R!452?PT*;%-^<^:E'W\CG^+J<I6#B)=F!0+
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M/6[HANWJ=-6P#9>B&>KIFN&)MI5FY;19V7$KMUHRJMJ=7'RMZ?FEF`Q$GH)V
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M?'B&]HG>`V;[',R7^Q8V06MWQGUA*GW^SO'6@7X[_T!>M1/[.[HIB&CUK$]$
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M^S?\%%#RKGCHB?3AM)8BV3.7W5*F#--ZD9:5`BZPG<-JM#4NC%K8U(C8&SO@
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MN),5=RRP$98PM;=E6)SU&=1JI6%4]8\:5T],*(CO$$07+>,,7$&!]@G6PI2R
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M4HLXQJGXH*X8HKC.>0/;4?_A3-R:LIEXI<^Y$&5%B>8?B48T8[`01&?TQNZ=
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>\,Y;ATP>0^,Y\-><H4<6'Y.K?<G_`Z+L!%(`6P``
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`
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end
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From owner-pgsql-hackers@hub.org Mon Oct 19 07:31:10 1998
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Received: from renoir.op.net (root@renoir.op.net [209.152.193.4])
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by candle.pha.pa.us (8.9.0/8.9.0) with ESMTP id HAA05591
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for <maillist@candle.pha.pa.us>; Mon, 19 Oct 1998 07:31:09 -0400 (EDT)
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Received: from hub.org (majordom@hub.org [209.47.148.200]) by renoir.op.net (o1/$ Revision: 1.18 $) with ESMTP id HAA13574 for <maillist@candle.pha.pa.us>; Mon, 19 Oct 1998 07:12:57 -0400 (EDT)
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for <pgsql-hackers@postgreSQL.org>; Mon, 19 Oct 1998 06:22:27 -0400 (EDT)
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id m0zVCaT-000EBPC; Mon, 19 Oct 98 12:30 MET DST
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Message-Id: <m0zVCaT-000EBPC@orion.SAPserv.Hamburg.dsh.de>
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From: jwieck@debis.com (Jan Wieck)
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Subject: Re: [HACKERS] What about LIMIT in SELECT ?
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To: Inoue@tpf.co.jp (Hiroshi Inoue)
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Date: Mon, 19 Oct 1998 12:30:52 +0200 (MET DST)
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Cc: jwieck@debis.com, pgsql-hackers@postgreSQL.org, maillist@candle.pha.pa.us
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Reply-To: jwieck@debis.com (Jan Wieck)
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In-Reply-To: <002801bdfb46$39ad8ec0$2801007e@cadzone.tpf.co.jp> from "Hiroshi Inoue" at Oct 19, 98 06:52:46 pm
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X-Mailer: ELM [version 2.4 PL25]
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Content-Type: text
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Sender: owner-pgsql-hackers@postgreSQL.org
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Precedence: bulk
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Status: RO
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Hiroshi Inoue wrote:
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> When using cursors,in most cases the response to get first(next) rows
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> is necessary for me,not the throughput.
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> How can we tell PostgreSQL optimzer that the response is necessary ?
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With my LIMIT patch, the offset and the row count are part of
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the querytree. And if a LIMIT is given, the limitCount elemet
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of the querytree (a Node *) isn't NULL what it is by default.
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When a LIMIT is given, the optimizer could assume that first
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rows is wanted (even if the limit is ALL maybe - but I have
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to think about this some more). And this assumption might let
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it decide to use an index to resolve an ORDER BY even if no
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qualification was given.
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Telling the optimizer that first rows wanted in a cursor
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operation would read
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DECLARE CURSOR c FOR SELECT * FROM mytab ORDER BY a LIMIT ALL;
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Jan
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--
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#======================================================================#
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# It's easier to get forgiveness for being wrong than for being right. #
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# Let's break this rule - forgive me. #
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#======================================== jwieck@debis.com (Jan Wieck) #
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From owner-pgsql-hackers@hub.org Tue Oct 20 06:01:49 1998
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Received: from renoir.op.net (root@renoir.op.net [209.152.193.4])
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by candle.pha.pa.us (8.9.0/8.9.0) with ESMTP id GAA02483
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for <maillist@candle.pha.pa.us>; Tue, 20 Oct 1998 06:01:48 -0400 (EDT)
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Received: from hub.org (majordom@hub.org [209.47.148.200]) by renoir.op.net (o1/$ Revision: 1.18 $) with ESMTP id FAA07799 for <maillist@candle.pha.pa.us>; Tue, 20 Oct 1998 05:51:19 -0400 (EDT)
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From: jwieck@debis.com (Jan Wieck)
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Subject: Re: [HACKERS] What about LIMIT in SELECT ?
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To: Inoue@tpf.co.jp (Hiroshi Inoue)
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Date: Tue, 20 Oct 1998 11:25:22 +0200 (MET DST)
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Cc: maillist@candle.pha.pa.us, jwieck@debis.com, hackers@postgreSQL.org
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Reply-To: jwieck@debis.com (Jan Wieck)
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In-Reply-To: <000601bdfc03$02e67100$2801007e@cadzone.tpf.co.jp> from "Hiroshi Inoue" at Oct 20, 98 05:24:09 pm
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X-Mailer: ELM [version 2.4 PL25]
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Content-Type: text
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Sender: owner-pgsql-hackers@postgreSQL.org
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Precedence: bulk
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Status: RO
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Hiroshi Inoue wrote:
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> > * Prevent psort() usage when query already using index matching ORDER BY
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> >
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> >
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>
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> I can't find the reference to descending order cases except my posting.
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> If we use an index scan to remove sorts in those cases,backward positioning
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> and scanning are necessary.
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I think it's only thought as a reminder that the optimizer
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needs some optimization.
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That topic, and the LIMIT stuff too I think, is past 6.4 work
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and may go into a 6.4.1 performance release. So when we are
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after 6.4, we have enough time to work out a real solution,
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instead of just throwing in a patch as a quick shot.
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What we two did where steps in the same direction. Your one
|
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covers more situations, but after all if multiple people have
|
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the same idea there is a good chance that it is the right
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thing to do.
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>
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> Let t be a table with 2 indices, index1(key1,key2), index2(key1,key3).
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> i.e. key1 is common to index1 and index2.
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>
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> And for the query
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> select * from t where key1>....;
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>
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> If PosgreSQL optimizer choose [ index scan on index1 ] we can't remove
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> sorts from the following query.
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> select * from t where key1>... order by key1,key3;
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>
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> Similarly if [ index scan on index2 ] are chosen we can't remove sorts
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> from the following query.
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> select * from t where key1>... order by key1,key2;
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>
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> But in both cases (clever) optimizer can choose another index for scan.
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Right. As I remember, your solution does basically the same
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as my one. It does not change the optimizers decision about
|
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the index or if an index at all is used. So I assume they
|
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hook into the same position where depending on the order by
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clause the sort node is added. And that is at the very end of
|
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the optimizer.
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What you describe above requires changes in upper levels of
|
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optimization. Doing that is far away from my knowledge about
|
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the optimizer. And some of your earlier statements let me
|
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think you aren't familiar enough with it too. We need at
|
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least help from others to do it well.
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I don't want to dive that deep into the optimizer. There was
|
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a far too long time where the rule system was broken and got
|
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out of sync with the parser/optimizer capabilities. I fixed
|
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many things in it for 6.4. My first priority now is, not to
|
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let such a situation come up again.
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Jan
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--
|
|
|
|
#======================================================================#
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|
# It's easier to get forgiveness for being wrong than for being right. #
|
|
# Let's break this rule - forgive me. #
|
|
#======================================== jwieck@debis.com (Jan Wieck) #
|
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From wieck@sapserv.debis.de Tue Oct 20 13:00:04 1998
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|
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From: jwieck@debis.com (Jan Wieck)
|
|
Subject: Re: [HACKERS] What about LIMIT in SELECT ?
|
|
To: maillist@candle.pha.pa.us (Bruce Momjian)
|
|
Date: Tue, 20 Oct 1998 19:12:19 +0200 (MET DST)
|
|
Cc: jwieck@debis.com, Inoue@tpf.co.jp, hackers@postgreSQL.org
|
|
Reply-To: jwieck@debis.com (Jan Wieck)
|
|
In-Reply-To: <199810201645.MAA07946@candle.pha.pa.us> from "Bruce Momjian" at Oct 20, 98 12:45:49 pm
|
|
X-Mailer: ELM [version 2.4 PL25]
|
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Content-Type: text
|
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Status: ROr
|
|
|
|
>
|
|
> I agree. Another good thing is that the LIMIT thing will not require a
|
|
> dump/reload, so it is a good candidate for a minor release.
|
|
|
|
That's wrong, sorry.
|
|
|
|
The limit thing as I implemented it adds 2 new variables to
|
|
the Query structure. Rewrite rules are stored as querytrees
|
|
and in the existing pg_rewrite entries that would be missing.
|
|
|
|
|
|
Jan
|
|
|
|
--
|
|
|
|
#======================================================================#
|
|
# It's easier to get forgiveness for being wrong than for being right. #
|
|
# Let's break this rule - forgive me. #
|
|
#======================================== jwieck@debis.com (Jan Wieck) #
|
|
|
|
|
|
|
|
From owner-pgsql-hackers@hub.org Tue Oct 20 13:24:47 1998
|
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|
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From: jwieck@debis.com (Jan Wieck)
|
|
Subject: Re: [HACKERS] What about LIMIT in SELECT ?
|
|
To: maillist@candle.pha.pa.us (Bruce Momjian)
|
|
Date: Tue, 20 Oct 1998 19:12:19 +0200 (MET DST)
|
|
Cc: jwieck@debis.com, Inoue@tpf.co.jp, hackers@postgreSQL.org
|
|
Reply-To: jwieck@debis.com (Jan Wieck)
|
|
In-Reply-To: <199810201645.MAA07946@candle.pha.pa.us> from "Bruce Momjian" at Oct 20, 98 12:45:49 pm
|
|
X-Mailer: ELM [version 2.4 PL25]
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Content-Type: text
|
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Sender: owner-pgsql-hackers@postgreSQL.org
|
|
Precedence: bulk
|
|
Status: ROr
|
|
|
|
>
|
|
> I agree. Another good thing is that the LIMIT thing will not require a
|
|
> dump/reload, so it is a good candidate for a minor release.
|
|
|
|
That's wrong, sorry.
|
|
|
|
The limit thing as I implemented it adds 2 new variables to
|
|
the Query structure. Rewrite rules are stored as querytrees
|
|
and in the existing pg_rewrite entries that would be missing.
|
|
|
|
|
|
Jan
|
|
|
|
--
|
|
|
|
#======================================================================#
|
|
# It's easier to get forgiveness for being wrong than for being right. #
|
|
# Let's break this rule - forgive me. #
|
|
#======================================== jwieck@debis.com (Jan Wieck) #
|
|
|
|
|
|
|
|
|
|
From wieck@sapserv.debis.de Tue Oct 20 13:10:22 1998
|
|
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for <maillist@candle.pha.pa.us>; Tue, 20 Oct 1998 13:10:18 -0400 (EDT)
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Message-Id: <m0zVfUW-000EBPC@orion.SAPserv.Hamburg.dsh.de>
|
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From: jwieck@debis.com (Jan Wieck)
|
|
Subject: Re: [HACKERS] What about LIMIT in SELECT ?
|
|
To: maillist@candle.pha.pa.us (Bruce Momjian)
|
|
Date: Tue, 20 Oct 1998 19:22:40 +0200 (MET DST)
|
|
Cc: jwieck@debis.com, Inoue@tpf.co.jp, hackers@postgreSQL.org
|
|
Reply-To: jwieck@debis.com (Jan Wieck)
|
|
In-Reply-To: <199810201702.NAA08286@candle.pha.pa.us> from "Bruce Momjian" at Oct 20, 98 01:02:58 pm
|
|
X-Mailer: ELM [version 2.4 PL25]
|
|
Content-Type: text
|
|
Status: RO
|
|
|
|
>
|
|
> > >
|
|
> > > I agree. Another good thing is that the LIMIT thing will not require a
|
|
> > > dump/reload, so it is a good candidate for a minor release.
|
|
> >
|
|
> > That's wrong, sorry.
|
|
> >
|
|
> > The limit thing as I implemented it adds 2 new variables to
|
|
> > the Query structure. Rewrite rules are stored as querytrees
|
|
> > and in the existing pg_rewrite entries that would be missing.
|
|
>
|
|
> Oh, sorry. I forgot. That could be tough.
|
|
|
|
But it wouldn't hurt to add them now to have them in
|
|
place. The required out-, read- and copyfuncs are in
|
|
my patch too. This would prevent dump/load when we
|
|
later add the real LIMIT functionality. And it does
|
|
not change anything now.
|
|
|
|
|
|
Jan
|
|
|
|
--
|
|
|
|
#======================================================================#
|
|
# It's easier to get forgiveness for being wrong than for being right. #
|
|
# Let's break this rule - forgive me. #
|
|
#======================================== jwieck@debis.com (Jan Wieck) #
|
|
|
|
|
|
From owner-pgsql-hackers@hub.org Tue Oct 20 14:57:36 1998
|
|
Received: from hub.org (majordom@hub.org [209.47.148.200])
|
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Message-Id: <m0zVfUW-000EBPC@orion.SAPserv.Hamburg.dsh.de>
|
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From: jwieck@debis.com (Jan Wieck)
|
|
Subject: Re: [HACKERS] What about LIMIT in SELECT ?
|
|
To: maillist@candle.pha.pa.us (Bruce Momjian)
|
|
Date: Tue, 20 Oct 1998 19:22:40 +0200 (MET DST)
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Cc: jwieck@debis.com, Inoue@tpf.co.jp, hackers@postgreSQL.org
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Reply-To: jwieck@debis.com (Jan Wieck)
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In-Reply-To: <199810201702.NAA08286@candle.pha.pa.us> from "Bruce Momjian" at Oct 20, 98 01:02:58 pm
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X-Mailer: ELM [version 2.4 PL25]
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Content-Type: text
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Sender: owner-pgsql-hackers@postgreSQL.org
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Precedence: bulk
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Status: ROr
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>
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> > >
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> > > I agree. Another good thing is that the LIMIT thing will not require a
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> > > dump/reload, so it is a good candidate for a minor release.
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> >
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> > That's wrong, sorry.
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> >
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> > The limit thing as I implemented it adds 2 new variables to
|
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> > the Query structure. Rewrite rules are stored as querytrees
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> > and in the existing pg_rewrite entries that would be missing.
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>
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> Oh, sorry. I forgot. That could be tough.
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|
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But it wouldn't hurt to add them now to have them in
|
|
place. The required out-, read- and copyfuncs are in
|
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my patch too. This would prevent dump/load when we
|
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later add the real LIMIT functionality. And it does
|
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not change anything now.
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|
|
|
|
Jan
|
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--
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|
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|
#======================================================================#
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# It's easier to get forgiveness for being wrong than for being right. #
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# Let's break this rule - forgive me. #
|
|
#======================================== jwieck@debis.com (Jan Wieck) #
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From owner-pgsql-hackers@hub.org Wed Oct 21 02:35:54 1998
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Received: from hub.org (majordom@hub.org [209.47.148.200])
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Wed, 21 Oct 1998 02:09:27 -0400 (EDT)
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From: Bruce Momjian <maillist@candle.pha.pa.us>
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Message-Id: <199810210609.CAA27774@candle.pha.pa.us>
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Subject: Re: [HACKERS] What about LIMIT in SELECT ?
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In-Reply-To: <m0zVfUW-000EBPC@orion.SAPserv.Hamburg.dsh.de> from Jan Wieck at "Oct 20, 1998 7:22:40 pm"
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To: jwieck@debis.com
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Date: Wed, 21 Oct 1998 02:09:26 -0400 (EDT)
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Cc: jwieck@debis.com, Inoue@tpf.co.jp, hackers@postgreSQL.org
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X-Mailer: ELM [version 2.4ME+ PL47 (25)]
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MIME-Version: 1.0
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Content-Type: text/plain; charset=US-ASCII
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Content-Transfer-Encoding: 7bit
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Sender: owner-pgsql-hackers@postgreSQL.org
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Precedence: bulk
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Status: RO
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|
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> >
|
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> > > >
|
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> > > > I agree. Another good thing is that the LIMIT thing will not require a
|
|
> > > > dump/reload, so it is a good candidate for a minor release.
|
|
> > >
|
|
> > > That's wrong, sorry.
|
|
> > >
|
|
> > > The limit thing as I implemented it adds 2 new variables to
|
|
> > > the Query structure. Rewrite rules are stored as querytrees
|
|
> > > and in the existing pg_rewrite entries that would be missing.
|
|
> >
|
|
> > Oh, sorry. I forgot. That could be tough.
|
|
>
|
|
> But it wouldn't hurt to add them now to have them in
|
|
> place. The required out-, read- and copyfuncs are in
|
|
> my patch too. This would prevent dump/load when we
|
|
> later add the real LIMIT functionality. And it does
|
|
> not change anything now.
|
|
>
|
|
|
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Jan, we found that I am having to require an initdb for the INET/CIDR
|
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type, so if you want stuff to change the views/rules for the limit
|
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addition post 6.4, please send them in and I will apply them.
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You clearly have the syntax down, so I think you should go ahead.
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|
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--
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|
Bruce Momjian | http://www.op.net/~candle
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maillist@candle.pha.pa.us | (610) 853-3000
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+ If your life is a hard drive, | 830 Blythe Avenue
|
|
+ Christ can be your backup. | Drexel Hill, Pennsylvania 19026
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From wieck@sapserv.debis.de Thu Oct 22 10:20:58 1998
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Received: from dsh.de (firewall-user@neptun.sns-felb.debis.de [53.122.101.2])
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by candle.pha.pa.us (8.9.0/8.9.0) with ESMTP id KAA20566
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for <maillist@candle.pha.pa.us>; Thu, 22 Oct 1998 10:20:54 -0400 (EDT)
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for maillist@candle.pha.pa.us
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id m0zWLoE-000EBPC; Thu, 22 Oct 98 16:33 MET DST
|
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Message-Id: <m0zWLoE-000EBPC@orion.SAPserv.Hamburg.dsh.de>
|
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From: jwieck@debis.com (Jan Wieck)
|
|
Subject: Re: [HACKERS] psql's help (the LIMIT stuff)
|
|
To: maillist@candle.pha.pa.us (Bruce Momjian)
|
|
Date: Thu, 22 Oct 1998 16:33:50 +0200 (MET DST)
|
|
Cc: jwieck@debis.com, jose@sferacarta.com, pgsql-hackers@postgreSQL.org
|
|
Reply-To: jwieck@debis.com (Jan Wieck)
|
|
In-Reply-To: <199810221351.JAA19663@candle.pha.pa.us> from "Bruce Momjian" at Oct 22, 98 09:51:19 am
|
|
X-Mailer: ELM [version 2.4 PL25]
|
|
Content-Type: text
|
|
Status: ROr
|
|
|
|
> >
|
|
> > I hope the QUERY_LIMIT too.
|
|
>
|
|
> I still have that cnfify() possible fix to review for KQSO. Are you
|
|
> still thinking limit for 6.4 final, or a minor release after that?
|
|
|
|
I posted the part that is the minimum applied to 6.4 to make
|
|
adding LIMIT later non-initdb earlier. Anyway, here it's
|
|
again.
|
|
|
|
My LIMIT implementation that does it like the SET in the
|
|
toplevel executor (but via parsetree values) is ready for
|
|
production. I only held it back because it's feature, not
|
|
bugfix.
|
|
|
|
Do you want it in 6.4 final?
|
|
|
|
|
|
Jan
|
|
|
|
--
|
|
|
|
#======================================================================#
|
|
# It's easier to get forgiveness for being wrong than for being right. #
|
|
# Let's break this rule - forgive me. #
|
|
#======================================== jwieck@debis.com (Jan Wieck) #
|
|
|
|
|
|
diff -cr src.orig/backend/nodes/copyfuncs.c src/backend/nodes/copyfuncs.c
|
|
*** src.orig/backend/nodes/copyfuncs.c Fri Oct 16 11:53:40 1998
|
|
--- src/backend/nodes/copyfuncs.c Fri Oct 16 13:32:35 1998
|
|
***************
|
|
*** 1578,1583 ****
|
|
--- 1578,1586 ----
|
|
newnode->unionClause = temp_list;
|
|
}
|
|
|
|
+ Node_Copy(from, newnode, limitOffset);
|
|
+ Node_Copy(from, newnode, limitCount);
|
|
+
|
|
return newnode;
|
|
}
|
|
|
|
diff -cr src.orig/backend/nodes/outfuncs.c src/backend/nodes/outfuncs.c
|
|
*** src.orig/backend/nodes/outfuncs.c Fri Oct 16 11:53:40 1998
|
|
--- src/backend/nodes/outfuncs.c Fri Oct 16 13:30:50 1998
|
|
***************
|
|
*** 259,264 ****
|
|
--- 259,268 ----
|
|
appendStringInfo(str, (node->hasSubLinks ? "true" : "false"));
|
|
appendStringInfo(str, " :unionClause ");
|
|
_outNode(str, node->unionClause);
|
|
+ appendStringInfo(str, " :limitOffset ");
|
|
+ _outNode(str, node->limitOffset);
|
|
+ appendStringInfo(str, " :limitCount ");
|
|
+ _outNode(str, node->limitCount);
|
|
}
|
|
|
|
static void
|
|
diff -cr src.orig/backend/nodes/readfuncs.c src/backend/nodes/readfuncs.c
|
|
*** src.orig/backend/nodes/readfuncs.c Fri Oct 16 11:53:40 1998
|
|
--- src/backend/nodes/readfuncs.c Fri Oct 16 13:31:43 1998
|
|
***************
|
|
*** 163,168 ****
|
|
--- 163,174 ----
|
|
token = lsptok(NULL, &length); /* skip :unionClause */
|
|
local_node->unionClause = nodeRead(true);
|
|
|
|
+ token = lsptok(NULL, &length); /* skip :limitOffset */
|
|
+ local_node->limitOffset = nodeRead(true);
|
|
+
|
|
+ token = lsptok(NULL, &length); /* skip :limitCount */
|
|
+ local_node->limitCount = nodeRead(true);
|
|
+
|
|
return local_node;
|
|
}
|
|
|
|
diff -cr src.orig/include/nodes/parsenodes.h src/include/nodes/parsenodes.h
|
|
*** src.orig/include/nodes/parsenodes.h Fri Oct 16 11:53:58 1998
|
|
--- src/include/nodes/parsenodes.h Fri Oct 16 13:35:32 1998
|
|
***************
|
|
*** 60,65 ****
|
|
--- 60,67 ----
|
|
|
|
List *unionClause; /* unions are linked under the previous
|
|
* query */
|
|
+ Node *limitOffset; /* # of result tuples to skip */
|
|
+ Node *limitCount; /* # of result tuples to return */
|
|
|
|
/* internal to planner */
|
|
List *base_rel_list; /* base relation list */
|
|
***************
|
|
*** 639,644 ****
|
|
--- 641,648 ----
|
|
char *portalname; /* the portal (cursor) to create */
|
|
bool binary; /* a binary (internal) portal? */
|
|
bool unionall; /* union without unique sort */
|
|
+ Node *limitOffset; /* # of result tuples to skip */
|
|
+ Node *limitCount; /* # of result tuples to return */
|
|
} SelectStmt;
|
|
|
|
|
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|
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From owner-pgsql-hackers@hub.org Thu Oct 22 11:33:41 1998
|
|
Received: from renoir.op.net (root@renoir.op.net [209.152.193.4])
|
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by candle.pha.pa.us (8.9.0/8.9.0) with ESMTP id LAA01724
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for <maillist@candle.pha.pa.us>; Thu, 22 Oct 1998 11:33:31 -0400 (EDT)
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Received: from hub.org (majordom@hub.org [209.47.148.200]) by renoir.op.net (o1/$ Revision: 1.18 $) with ESMTP id LAA12702 for <maillist@candle.pha.pa.us>; Thu, 22 Oct 1998 11:25:02 -0400 (EDT)
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for <pgsql-hackers@postgreSQL.org>; Thu, 22 Oct 1998 10:21:00 -0400 (EDT)
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Thu, 22 Oct 1998 16:19:55 +0200 (MET DST)
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Received: from mars.SAPserv.Hamburg.dsh.de (root@mail5.hh1.dsh.de [53.2.168.17])
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by mail1.hh1.dsh.de (8.8.7/8.8.7) with SMTP id QAA18978;
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by mars.SAPserv.Hamburg.dsh.de with smtp
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id m0zWJG2-000B5AC; Thu, 22 Oct 98 13:50 MET DST
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Received: by orion.SAPserv.Hamburg.dsh.de
|
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for maillist@candle.pha.pa.us
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id m0zWLoE-000EBPC; Thu, 22 Oct 98 16:33 MET DST
|
|
Message-Id: <m0zWLoE-000EBPC@orion.SAPserv.Hamburg.dsh.de>
|
|
From: jwieck@debis.com (Jan Wieck)
|
|
Subject: Re: [HACKERS] psql's help (the LIMIT stuff)
|
|
To: maillist@candle.pha.pa.us (Bruce Momjian)
|
|
Date: Thu, 22 Oct 1998 16:33:50 +0200 (MET DST)
|
|
Cc: jwieck@debis.com, jose@sferacarta.com, pgsql-hackers@postgreSQL.org
|
|
Reply-To: jwieck@debis.com (Jan Wieck)
|
|
In-Reply-To: <199810221351.JAA19663@candle.pha.pa.us> from "Bruce Momjian" at Oct 22, 98 09:51:19 am
|
|
X-Mailer: ELM [version 2.4 PL25]
|
|
Content-Type: text
|
|
Sender: owner-pgsql-hackers@postgreSQL.org
|
|
Precedence: bulk
|
|
Status: RO
|
|
|
|
> >
|
|
> > I hope the QUERY_LIMIT too.
|
|
>
|
|
> I still have that cnfify() possible fix to review for KQSO. Are you
|
|
> still thinking limit for 6.4 final, or a minor release after that?
|
|
|
|
I posted the part that is the minimum applied to 6.4 to make
|
|
adding LIMIT later non-initdb earlier. Anyway, here it's
|
|
again.
|
|
|
|
My LIMIT implementation that does it like the SET in the
|
|
toplevel executor (but via parsetree values) is ready for
|
|
production. I only held it back because it's feature, not
|
|
bugfix.
|
|
|
|
Do you want it in 6.4 final?
|
|
|
|
|
|
Jan
|
|
|
|
--
|
|
|
|
#======================================================================#
|
|
# It's easier to get forgiveness for being wrong than for being right. #
|
|
# Let's break this rule - forgive me. #
|
|
#======================================== jwieck@debis.com (Jan Wieck) #
|
|
|
|
|
|
diff -cr src.orig/backend/nodes/copyfuncs.c src/backend/nodes/copyfuncs.c
|
|
*** src.orig/backend/nodes/copyfuncs.c Fri Oct 16 11:53:40 1998
|
|
--- src/backend/nodes/copyfuncs.c Fri Oct 16 13:32:35 1998
|
|
***************
|
|
*** 1578,1583 ****
|
|
--- 1578,1586 ----
|
|
newnode->unionClause = temp_list;
|
|
}
|
|
|
|
+ Node_Copy(from, newnode, limitOffset);
|
|
+ Node_Copy(from, newnode, limitCount);
|
|
+
|
|
return newnode;
|
|
}
|
|
|
|
diff -cr src.orig/backend/nodes/outfuncs.c src/backend/nodes/outfuncs.c
|
|
*** src.orig/backend/nodes/outfuncs.c Fri Oct 16 11:53:40 1998
|
|
--- src/backend/nodes/outfuncs.c Fri Oct 16 13:30:50 1998
|
|
***************
|
|
*** 259,264 ****
|
|
--- 259,268 ----
|
|
appendStringInfo(str, (node->hasSubLinks ? "true" : "false"));
|
|
appendStringInfo(str, " :unionClause ");
|
|
_outNode(str, node->unionClause);
|
|
+ appendStringInfo(str, " :limitOffset ");
|
|
+ _outNode(str, node->limitOffset);
|
|
+ appendStringInfo(str, " :limitCount ");
|
|
+ _outNode(str, node->limitCount);
|
|
}
|
|
|
|
static void
|
|
diff -cr src.orig/backend/nodes/readfuncs.c src/backend/nodes/readfuncs.c
|
|
*** src.orig/backend/nodes/readfuncs.c Fri Oct 16 11:53:40 1998
|
|
--- src/backend/nodes/readfuncs.c Fri Oct 16 13:31:43 1998
|
|
***************
|
|
*** 163,168 ****
|
|
--- 163,174 ----
|
|
token = lsptok(NULL, &length); /* skip :unionClause */
|
|
local_node->unionClause = nodeRead(true);
|
|
|
|
+ token = lsptok(NULL, &length); /* skip :limitOffset */
|
|
+ local_node->limitOffset = nodeRead(true);
|
|
+
|
|
+ token = lsptok(NULL, &length); /* skip :limitCount */
|
|
+ local_node->limitCount = nodeRead(true);
|
|
+
|
|
return local_node;
|
|
}
|
|
|
|
diff -cr src.orig/include/nodes/parsenodes.h src/include/nodes/parsenodes.h
|
|
*** src.orig/include/nodes/parsenodes.h Fri Oct 16 11:53:58 1998
|
|
--- src/include/nodes/parsenodes.h Fri Oct 16 13:35:32 1998
|
|
***************
|
|
*** 60,65 ****
|
|
--- 60,67 ----
|
|
|
|
List *unionClause; /* unions are linked under the previous
|
|
* query */
|
|
+ Node *limitOffset; /* # of result tuples to skip */
|
|
+ Node *limitCount; /* # of result tuples to return */
|
|
|
|
/* internal to planner */
|
|
List *base_rel_list; /* base relation list */
|
|
***************
|
|
*** 639,644 ****
|
|
--- 641,648 ----
|
|
char *portalname; /* the portal (cursor) to create */
|
|
bool binary; /* a binary (internal) portal? */
|
|
bool unionall; /* union without unique sort */
|
|
+ Node *limitOffset; /* # of result tuples to skip */
|
|
+ Node *limitCount; /* # of result tuples to return */
|
|
} SelectStmt;
|
|
|
|
|
|
|
|
|
|
From wieck@sapserv.debis.de Thu Oct 22 11:01:05 1998
|
|
Received: from renoir.op.net (root@renoir.op.net [209.152.193.4])
|
|
by candle.pha.pa.us (8.9.0/8.9.0) with ESMTP id LAA21185
|
|
for <maillist@candle.pha.pa.us>; Thu, 22 Oct 1998 11:01:00 -0400 (EDT)
|
|
Received: from dsh.de (firewall-user@neptun.sns-felb.debis.de [53.122.101.2]) by renoir.op.net (o1/$ Revision: 1.18 $) with ESMTP id KAA09646 for <maillist@candle.pha.pa.us>; Thu, 22 Oct 1998 10:44:36 -0400 (EDT)
|
|
Received: by dsh.de; id QAA19394; Thu, 22 Oct 1998 16:43:42 +0200 (MET DST)
|
|
Received: from dshmail.dsh.de(53.47.15.3) by neptun.dsh.de via smap (3.2)
|
|
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Received: from mail1.hh1.dsh.de (mail1.hh1.dsh.de [53.47.9.5])
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|
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|
|
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|
|
Received: from mars.SAPserv.Hamburg.dsh.de (root@mail5.hh1.dsh.de [53.2.168.17])
|
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|
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|
|
by mars.SAPserv.Hamburg.dsh.de with smtp
|
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|
|
id m0zWJWL-000B5DC; Thu, 22 Oct 98 14:07 MET DST
|
|
Received: by orion.SAPserv.Hamburg.dsh.de
|
|
for maillist@candle.pha.pa.us
|
|
id m0zWM4W-000EBPC; Thu, 22 Oct 98 16:50 MET DST
|
|
Message-Id: <m0zWM4W-000EBPC@orion.SAPserv.Hamburg.dsh.de>
|
|
From: jwieck@debis.com (Jan Wieck)
|
|
Subject: Re: [HACKERS] psql's help (the LIMIT stuff)
|
|
To: maillist@candle.pha.pa.us (Bruce Momjian)
|
|
Date: Thu, 22 Oct 1998 16:50:40 +0200 (MET DST)
|
|
Cc: jwieck@debis.com, jose@sferacarta.com, pgsql-hackers@postgreSQL.org
|
|
Reply-To: jwieck@debis.com (Jan Wieck)
|
|
In-Reply-To: <199810221424.KAA20601@candle.pha.pa.us> from "Bruce Momjian" at Oct 22, 98 10:24:08 am
|
|
X-Mailer: ELM [version 2.4 PL25]
|
|
Content-Type: text
|
|
Status: RO
|
|
|
|
>
|
|
> > > >
|
|
> > > > I hope the QUERY_LIMIT too.
|
|
> > >
|
|
> > > I still have that cnfify() possible fix to review for KQSO. Are you
|
|
> > > still thinking limit for 6.4 final, or a minor release after that?
|
|
> >
|
|
> > I posted the part that is the minimum applied to 6.4 to make
|
|
> > adding LIMIT later non-initdb earlier. Anyway, here it's
|
|
> > again.
|
|
>
|
|
> Already applied. I assume it is the same as the one I applied.
|
|
|
|
Seen, thanks. Your 'Applied' just arrived after I packed it
|
|
again. It's the same.
|
|
|
|
> We are close to final, and can easily put it in 6.4.1, which I am sure
|
|
> we will need, and if we split CVS trees, you'll have lots of minor
|
|
> versions to pick from. :-)
|
|
>
|
|
> Seems like it would be a nice minor release item, but the problem is
|
|
> that minor releases aren't tested as much as major ones. How confident
|
|
> are you in the code? What do others thing?
|
|
|
|
I regression tested it, and did additional tests in the
|
|
SPI/PL area. It works. It only touches the parser and the
|
|
executor. Rules, planner/optimizer just bypass the values in
|
|
the parsetree. The parser and the executor are parts of
|
|
Postgres I feel very familiar with (not so in the optimizer).
|
|
I trust in the code and would use it in a production
|
|
environment.
|
|
|
|
It's below.
|
|
|
|
|
|
Jan
|
|
|
|
--
|
|
|
|
#======================================================================#
|
|
# It's easier to get forgiveness for being wrong than for being right. #
|
|
# Let's break this rule - forgive me. #
|
|
#======================================== jwieck@debis.com (Jan Wieck) #
|
|
|
|
|
|
diff -cr src.orig/backend/commands/command.c src/backend/commands/command.c
|
|
*** src.orig/backend/commands/command.c Fri Oct 16 11:53:38 1998
|
|
--- src/backend/commands/command.c Fri Oct 16 12:56:44 1998
|
|
***************
|
|
*** 39,44 ****
|
|
--- 39,45 ----
|
|
#include "utils/mcxt.h"
|
|
#include "utils/portal.h"
|
|
#include "utils/syscache.h"
|
|
+ #include "string.h"
|
|
|
|
/* ----------------
|
|
* PortalExecutorHeapMemory stuff
|
|
***************
|
|
*** 101,106 ****
|
|
--- 102,108 ----
|
|
int feature;
|
|
QueryDesc *queryDesc;
|
|
MemoryContext context;
|
|
+ Const limcount;
|
|
|
|
/* ----------------
|
|
* sanity checks
|
|
***************
|
|
*** 113,118 ****
|
|
--- 115,134 ----
|
|
}
|
|
|
|
/* ----------------
|
|
+ * Create a const node from the given count value
|
|
+ * ----------------
|
|
+ */
|
|
+ memset(&limcount, 0, sizeof(limcount));
|
|
+ limcount.type = T_Const;
|
|
+ limcount.consttype = INT4OID;
|
|
+ limcount.constlen = sizeof(int4);
|
|
+ limcount.constvalue = (Datum)count;
|
|
+ limcount.constisnull = FALSE;
|
|
+ limcount.constbyval = TRUE;
|
|
+ limcount.constisset = FALSE;
|
|
+ limcount.constiscast = FALSE;
|
|
+
|
|
+ /* ----------------
|
|
* get the portal from the portal name
|
|
* ----------------
|
|
*/
|
|
***************
|
|
*** 176,182 ****
|
|
PortalExecutorHeapMemory = (MemoryContext)
|
|
PortalGetHeapMemory(portal);
|
|
|
|
! ExecutorRun(queryDesc, PortalGetState(portal), feature, count);
|
|
|
|
if (dest == None) /* MOVE */
|
|
pfree(queryDesc);
|
|
--- 192,198 ----
|
|
PortalExecutorHeapMemory = (MemoryContext)
|
|
PortalGetHeapMemory(portal);
|
|
|
|
! ExecutorRun(queryDesc, PortalGetState(portal), feature, (Node *)NULL, (Node *)&limcount);
|
|
|
|
if (dest == None) /* MOVE */
|
|
pfree(queryDesc);
|
|
diff -cr src.orig/backend/executor/execMain.c src/backend/executor/execMain.c
|
|
*** src.orig/backend/executor/execMain.c Fri Oct 16 11:53:38 1998
|
|
--- src/backend/executor/execMain.c Fri Oct 16 20:05:19 1998
|
|
***************
|
|
*** 64,69 ****
|
|
--- 64,70 ----
|
|
static void EndPlan(Plan *plan, EState *estate);
|
|
static TupleTableSlot *ExecutePlan(EState *estate, Plan *plan,
|
|
Query *parseTree, CmdType operation,
|
|
+ int offsetTuples,
|
|
int numberTuples, ScanDirection direction,
|
|
void (*printfunc) ());
|
|
static void ExecRetrieve(TupleTableSlot *slot, void (*printfunc) (),
|
|
***************
|
|
*** 163,169 ****
|
|
* ----------------------------------------------------------------
|
|
*/
|
|
TupleTableSlot *
|
|
! ExecutorRun(QueryDesc *queryDesc, EState *estate, int feature, int count)
|
|
{
|
|
CmdType operation;
|
|
Query *parseTree;
|
|
--- 164,170 ----
|
|
* ----------------------------------------------------------------
|
|
*/
|
|
TupleTableSlot *
|
|
! ExecutorRun(QueryDesc *queryDesc, EState *estate, int feature, Node *limoffset, Node *limcount)
|
|
{
|
|
CmdType operation;
|
|
Query *parseTree;
|
|
***************
|
|
*** 171,176 ****
|
|
--- 172,179 ----
|
|
TupleTableSlot *result;
|
|
CommandDest dest;
|
|
void (*destination) ();
|
|
+ int offset = 0;
|
|
+ int count = 0;
|
|
|
|
/******************
|
|
* sanity checks
|
|
***************
|
|
*** 191,196 ****
|
|
--- 194,289 ----
|
|
estate->es_processed = 0;
|
|
estate->es_lastoid = InvalidOid;
|
|
|
|
+ /******************
|
|
+ * if given get the offset of the LIMIT clause
|
|
+ ******************
|
|
+ */
|
|
+ if (limoffset != NULL)
|
|
+ {
|
|
+ Const *coffset;
|
|
+ Param *poffset;
|
|
+ ParamListInfo paramLI;
|
|
+ int i;
|
|
+
|
|
+ switch (nodeTag(limoffset))
|
|
+ {
|
|
+ case T_Const:
|
|
+ coffset = (Const *)limoffset;
|
|
+ offset = (int)(coffset->constvalue);
|
|
+ break;
|
|
+
|
|
+ case T_Param:
|
|
+ poffset = (Param *)limoffset;
|
|
+ paramLI = estate->es_param_list_info;
|
|
+
|
|
+ if (paramLI == NULL)
|
|
+ elog(ERROR, "parameter for limit offset not in executor state");
|
|
+ for (i = 0; paramLI[i].kind != PARAM_INVALID; i++)
|
|
+ {
|
|
+ if (paramLI[i].kind == PARAM_NUM && paramLI[i].id == poffset->paramid)
|
|
+ break;
|
|
+ }
|
|
+ if (paramLI[i].kind == PARAM_INVALID)
|
|
+ elog(ERROR, "parameter for limit offset not in executor state");
|
|
+ if (paramLI[i].isnull)
|
|
+ elog(ERROR, "limit offset cannot be NULL value");
|
|
+ offset = (int)(paramLI[i].value);
|
|
+
|
|
+ break;
|
|
+
|
|
+ default:
|
|
+ elog(ERROR, "unexpected node type %d as limit offset", nodeTag(limoffset));
|
|
+ }
|
|
+
|
|
+ if (offset < 0)
|
|
+ elog(ERROR, "limit offset cannot be negative");
|
|
+ }
|
|
+
|
|
+ /******************
|
|
+ * if given get the count of the LIMIT clause
|
|
+ ******************
|
|
+ */
|
|
+ if (limcount != NULL)
|
|
+ {
|
|
+ Const *ccount;
|
|
+ Param *pcount;
|
|
+ ParamListInfo paramLI;
|
|
+ int i;
|
|
+
|
|
+ switch (nodeTag(limcount))
|
|
+ {
|
|
+ case T_Const:
|
|
+ ccount = (Const *)limcount;
|
|
+ count = (int)(ccount->constvalue);
|
|
+ break;
|
|
+
|
|
+ case T_Param:
|
|
+ pcount = (Param *)limcount;
|
|
+ paramLI = estate->es_param_list_info;
|
|
+
|
|
+ if (paramLI == NULL)
|
|
+ elog(ERROR, "parameter for limit count not in executor state");
|
|
+ for (i = 0; paramLI[i].kind != PARAM_INVALID; i++)
|
|
+ {
|
|
+ if (paramLI[i].kind == PARAM_NUM && paramLI[i].id == pcount->paramid)
|
|
+ break;
|
|
+ }
|
|
+ if (paramLI[i].kind == PARAM_INVALID)
|
|
+ elog(ERROR, "parameter for limit count not in executor state");
|
|
+ if (paramLI[i].isnull)
|
|
+ elog(ERROR, "limit count cannot be NULL value");
|
|
+ count = (int)(paramLI[i].value);
|
|
+
|
|
+ break;
|
|
+
|
|
+ default:
|
|
+ elog(ERROR, "unexpected node type %d as limit count", nodeTag(limcount));
|
|
+ }
|
|
+
|
|
+ if (count < 0)
|
|
+ elog(ERROR, "limit count cannot be negative");
|
|
+ }
|
|
+
|
|
switch (feature)
|
|
{
|
|
|
|
***************
|
|
*** 199,205 ****
|
|
plan,
|
|
parseTree,
|
|
operation,
|
|
! ALL_TUPLES,
|
|
ForwardScanDirection,
|
|
destination);
|
|
break;
|
|
--- 292,299 ----
|
|
plan,
|
|
parseTree,
|
|
operation,
|
|
! offset,
|
|
! count,
|
|
ForwardScanDirection,
|
|
destination);
|
|
break;
|
|
***************
|
|
*** 208,213 ****
|
|
--- 302,308 ----
|
|
plan,
|
|
parseTree,
|
|
operation,
|
|
+ offset,
|
|
count,
|
|
ForwardScanDirection,
|
|
destination);
|
|
***************
|
|
*** 222,227 ****
|
|
--- 317,323 ----
|
|
plan,
|
|
parseTree,
|
|
operation,
|
|
+ offset,
|
|
count,
|
|
BackwardScanDirection,
|
|
destination);
|
|
***************
|
|
*** 237,242 ****
|
|
--- 333,339 ----
|
|
plan,
|
|
parseTree,
|
|
operation,
|
|
+ 0,
|
|
ONE_TUPLE,
|
|
ForwardScanDirection,
|
|
destination);
|
|
***************
|
|
*** 691,696 ****
|
|
--- 788,794 ----
|
|
Plan *plan,
|
|
Query *parseTree,
|
|
CmdType operation,
|
|
+ int offsetTuples,
|
|
int numberTuples,
|
|
ScanDirection direction,
|
|
void (*printfunc) ())
|
|
***************
|
|
*** 742,747 ****
|
|
--- 840,859 ----
|
|
{
|
|
result = NULL;
|
|
break;
|
|
+ }
|
|
+
|
|
+ /******************
|
|
+ * For now we completely execute the plan and skip
|
|
+ * result tuples if requested by LIMIT offset.
|
|
+ * Finally we should try to do it in deeper levels
|
|
+ * if possible (during index scan)
|
|
+ * - Jan
|
|
+ ******************
|
|
+ */
|
|
+ if (offsetTuples > 0)
|
|
+ {
|
|
+ --offsetTuples;
|
|
+ continue;
|
|
}
|
|
|
|
/******************
|
|
diff -cr src.orig/backend/executor/functions.c src/backend/executor/functions.c
|
|
*** src.orig/backend/executor/functions.c Fri Oct 16 11:53:38 1998
|
|
--- src/backend/executor/functions.c Fri Oct 16 19:01:02 1998
|
|
***************
|
|
*** 130,135 ****
|
|
--- 130,138 ----
|
|
None);
|
|
estate = CreateExecutorState();
|
|
|
|
+ if (queryTree->limitOffset != NULL || queryTree->limitCount != NULL)
|
|
+ elog(ERROR, "LIMIT clause from SQL functions not yet implemented");
|
|
+
|
|
if (nargs > 0)
|
|
{
|
|
int i;
|
|
***************
|
|
*** 200,206 ****
|
|
|
|
feature = (LAST_POSTQUEL_COMMAND(es)) ? EXEC_RETONE : EXEC_RUN;
|
|
|
|
! return ExecutorRun(es->qd, es->estate, feature, 0);
|
|
}
|
|
|
|
static void
|
|
--- 203,209 ----
|
|
|
|
feature = (LAST_POSTQUEL_COMMAND(es)) ? EXEC_RETONE : EXEC_RUN;
|
|
|
|
! return ExecutorRun(es->qd, es->estate, feature, (Node *)NULL, (Node *)NULL);
|
|
}
|
|
|
|
static void
|
|
diff -cr src.orig/backend/executor/spi.c src/backend/executor/spi.c
|
|
*** src.orig/backend/executor/spi.c Fri Oct 16 11:53:39 1998
|
|
--- src/backend/executor/spi.c Fri Oct 16 19:25:33 1998
|
|
***************
|
|
*** 791,796 ****
|
|
--- 791,798 ----
|
|
bool isRetrieveIntoRelation = false;
|
|
char *intoName = NULL;
|
|
int res;
|
|
+ Const tcount_const;
|
|
+ Node *count = NULL;
|
|
|
|
switch (operation)
|
|
{
|
|
***************
|
|
*** 825,830 ****
|
|
--- 827,865 ----
|
|
return SPI_ERROR_OPUNKNOWN;
|
|
}
|
|
|
|
+ /* ----------------
|
|
+ * Get the query LIMIT tuple count
|
|
+ * ----------------
|
|
+ */
|
|
+ if (parseTree->limitCount != NULL)
|
|
+ {
|
|
+ /* ----------------
|
|
+ * A limit clause in the parsetree overrides the
|
|
+ * tcount parameter
|
|
+ * ----------------
|
|
+ */
|
|
+ count = parseTree->limitCount;
|
|
+ }
|
|
+ else
|
|
+ {
|
|
+ /* ----------------
|
|
+ * No LIMIT clause in parsetree. Use a local Const node
|
|
+ * to put tcount into it
|
|
+ * ----------------
|
|
+ */
|
|
+ memset(&tcount_const, 0, sizeof(tcount_const));
|
|
+ tcount_const.type = T_Const;
|
|
+ tcount_const.consttype = INT4OID;
|
|
+ tcount_const.constlen = sizeof(int4);
|
|
+ tcount_const.constvalue = (Datum)tcount;
|
|
+ tcount_const.constisnull = FALSE;
|
|
+ tcount_const.constbyval = TRUE;
|
|
+ tcount_const.constisset = FALSE;
|
|
+ tcount_const.constiscast = FALSE;
|
|
+
|
|
+ count = (Node *)&tcount_const;
|
|
+ }
|
|
+
|
|
if (state == NULL) /* plan preparation */
|
|
return res;
|
|
#ifdef SPI_EXECUTOR_STATS
|
|
***************
|
|
*** 845,851 ****
|
|
return SPI_OK_CURSOR;
|
|
}
|
|
|
|
! ExecutorRun(queryDesc, state, EXEC_FOR, tcount);
|
|
|
|
_SPI_current->processed = state->es_processed;
|
|
if (operation == CMD_SELECT && queryDesc->dest == SPI)
|
|
--- 880,886 ----
|
|
return SPI_OK_CURSOR;
|
|
}
|
|
|
|
! ExecutorRun(queryDesc, state, EXEC_FOR, parseTree->limitOffset, count);
|
|
|
|
_SPI_current->processed = state->es_processed;
|
|
if (operation == CMD_SELECT && queryDesc->dest == SPI)
|
|
diff -cr src.orig/backend/parser/analyze.c src/backend/parser/analyze.c
|
|
*** src.orig/backend/parser/analyze.c Fri Oct 16 11:53:41 1998
|
|
--- src/backend/parser/analyze.c Fri Oct 16 13:29:27 1998
|
|
***************
|
|
*** 180,186 ****
|
|
--- 180,190 ----
|
|
|
|
case T_SelectStmt:
|
|
if (!((SelectStmt *) parseTree)->portalname)
|
|
+ {
|
|
result = transformSelectStmt(pstate, (SelectStmt *) parseTree);
|
|
+ result->limitOffset = ((SelectStmt *)parseTree)->limitOffset;
|
|
+ result->limitCount = ((SelectStmt *)parseTree)->limitCount;
|
|
+ }
|
|
else
|
|
result = transformCursorStmt(pstate, (SelectStmt *) parseTree);
|
|
break;
|
|
diff -cr src.orig/backend/parser/gram.y src/backend/parser/gram.y
|
|
*** src.orig/backend/parser/gram.y Fri Oct 16 11:53:42 1998
|
|
--- src/backend/parser/gram.y Sun Oct 18 22:20:36 1998
|
|
***************
|
|
*** 45,50 ****
|
|
--- 45,51 ----
|
|
#include "catalog/catname.h"
|
|
#include "utils/elog.h"
|
|
#include "access/xact.h"
|
|
+ #include "catalog/pg_type.h"
|
|
|
|
#ifdef MULTIBYTE
|
|
#include "mb/pg_wchar.h"
|
|
***************
|
|
*** 163,169 ****
|
|
sort_clause, sortby_list, index_params, index_list, name_list,
|
|
from_clause, from_list, opt_array_bounds, nest_array_bounds,
|
|
expr_list, attrs, res_target_list, res_target_list2,
|
|
! def_list, opt_indirection, group_clause, TriggerFuncArgs
|
|
|
|
%type <node> func_return
|
|
%type <boolean> set_opt
|
|
--- 164,171 ----
|
|
sort_clause, sortby_list, index_params, index_list, name_list,
|
|
from_clause, from_list, opt_array_bounds, nest_array_bounds,
|
|
expr_list, attrs, res_target_list, res_target_list2,
|
|
! def_list, opt_indirection, group_clause, TriggerFuncArgs,
|
|
! opt_select_limit
|
|
|
|
%type <node> func_return
|
|
%type <boolean> set_opt
|
|
***************
|
|
*** 192,197 ****
|
|
--- 194,201 ----
|
|
|
|
%type <ival> fetch_how_many
|
|
|
|
+ %type <node> select_limit_value select_offset_value
|
|
+
|
|
%type <list> OptSeqList
|
|
%type <defelt> OptSeqElem
|
|
|
|
***************
|
|
*** 267,273 ****
|
|
FALSE_P, FETCH, FLOAT, FOR, FOREIGN, FROM, FULL,
|
|
GRANT, GROUP, HAVING, HOUR_P,
|
|
IN, INNER_P, INSENSITIVE, INSERT, INTERVAL, INTO, IS,
|
|
! JOIN, KEY, LANGUAGE, LEADING, LEFT, LIKE, LOCAL,
|
|
MATCH, MINUTE_P, MONTH_P, NAMES,
|
|
NATIONAL, NATURAL, NCHAR, NEXT, NO, NOT, NULL_P, NUMERIC,
|
|
OF, ON, ONLY, OPTION, OR, ORDER, OUTER_P,
|
|
--- 271,277 ----
|
|
FALSE_P, FETCH, FLOAT, FOR, FOREIGN, FROM, FULL,
|
|
GRANT, GROUP, HAVING, HOUR_P,
|
|
IN, INNER_P, INSENSITIVE, INSERT, INTERVAL, INTO, IS,
|
|
! JOIN, KEY, LANGUAGE, LEADING, LEFT, LIKE, LIMIT, LOCAL,
|
|
MATCH, MINUTE_P, MONTH_P, NAMES,
|
|
NATIONAL, NATURAL, NCHAR, NEXT, NO, NOT, NULL_P, NUMERIC,
|
|
OF, ON, ONLY, OPTION, OR, ORDER, OUTER_P,
|
|
***************
|
|
*** 299,305 ****
|
|
INCREMENT, INDEX, INHERITS, INSTEAD, ISNULL,
|
|
LANCOMPILER, LISTEN, LOAD, LOCATION, LOCK_P, MAXVALUE, MINVALUE, MOVE,
|
|
NEW, NOCREATEDB, NOCREATEUSER, NONE, NOTHING, NOTIFY, NOTNULL,
|
|
! OIDS, OPERATOR, PASSWORD, PROCEDURAL,
|
|
RECIPE, RENAME, RESET, RETURNS, ROW, RULE,
|
|
SEQUENCE, SERIAL, SETOF, SHOW, START, STATEMENT, STDIN, STDOUT, TRUSTED,
|
|
UNLISTEN, UNTIL, VACUUM, VALID, VERBOSE, VERSION
|
|
--- 303,309 ----
|
|
INCREMENT, INDEX, INHERITS, INSTEAD, ISNULL,
|
|
LANCOMPILER, LISTEN, LOAD, LOCATION, LOCK_P, MAXVALUE, MINVALUE, MOVE,
|
|
NEW, NOCREATEDB, NOCREATEUSER, NONE, NOTHING, NOTIFY, NOTNULL,
|
|
! OFFSET, OIDS, OPERATOR, PASSWORD, PROCEDURAL,
|
|
RECIPE, RENAME, RESET, RETURNS, ROW, RULE,
|
|
SEQUENCE, SERIAL, SETOF, SHOW, START, STATEMENT, STDIN, STDOUT, TRUSTED,
|
|
UNLISTEN, UNTIL, VACUUM, VALID, VERBOSE, VERSION
|
|
***************
|
|
*** 2591,2596 ****
|
|
--- 2595,2601 ----
|
|
result from_clause where_clause
|
|
group_clause having_clause
|
|
union_clause sort_clause
|
|
+ opt_select_limit
|
|
{
|
|
SelectStmt *n = makeNode(SelectStmt);
|
|
n->unique = $2;
|
|
***************
|
|
*** 2602,2607 ****
|
|
--- 2607,2622 ----
|
|
n->havingClause = $8;
|
|
n->unionClause = $9;
|
|
n->sortClause = $10;
|
|
+ if ($11 != NIL)
|
|
+ {
|
|
+ n->limitOffset = nth(0, $11);
|
|
+ n->limitCount = nth(1, $11);
|
|
+ }
|
|
+ else
|
|
+ {
|
|
+ n->limitOffset = NULL;
|
|
+ n->limitCount = NULL;
|
|
+ }
|
|
$$ = (Node *)n;
|
|
}
|
|
;
|
|
***************
|
|
*** 2699,2704 ****
|
|
--- 2714,2794 ----
|
|
| ASC { $$ = "<"; }
|
|
| DESC { $$ = ">"; }
|
|
| /*EMPTY*/ { $$ = "<"; /*default*/ }
|
|
+ ;
|
|
+
|
|
+ opt_select_limit: LIMIT select_offset_value ',' select_limit_value
|
|
+ { $$ = lappend(lappend(NIL, $2), $4); }
|
|
+ | LIMIT select_limit_value OFFSET select_offset_value
|
|
+ { $$ = lappend(lappend(NIL, $4), $2); }
|
|
+ | LIMIT select_limit_value
|
|
+ { $$ = lappend(lappend(NIL, NULL), $2); }
|
|
+ | OFFSET select_offset_value LIMIT select_limit_value
|
|
+ { $$ = lappend(lappend(NIL, $2), $4); }
|
|
+ | OFFSET select_offset_value
|
|
+ { $$ = lappend(lappend(NIL, $2), NULL); }
|
|
+ | /* EMPTY */
|
|
+ { $$ = NIL; }
|
|
+ ;
|
|
+
|
|
+ select_limit_value: Iconst
|
|
+ {
|
|
+ Const *n = makeNode(Const);
|
|
+
|
|
+ if ($1 < 1)
|
|
+ elog(ERROR, "selection limit must be ALL or a positive integer value > 0");
|
|
+
|
|
+ n->consttype = INT4OID;
|
|
+ n->constlen = sizeof(int4);
|
|
+ n->constvalue = (Datum)$1;
|
|
+ n->constisnull = FALSE;
|
|
+ n->constbyval = TRUE;
|
|
+ n->constisset = FALSE;
|
|
+ n->constiscast = FALSE;
|
|
+ $$ = (Node *)n;
|
|
+ }
|
|
+ | ALL
|
|
+ {
|
|
+ Const *n = makeNode(Const);
|
|
+ n->consttype = INT4OID;
|
|
+ n->constlen = sizeof(int4);
|
|
+ n->constvalue = (Datum)0;
|
|
+ n->constisnull = FALSE;
|
|
+ n->constbyval = TRUE;
|
|
+ n->constisset = FALSE;
|
|
+ n->constiscast = FALSE;
|
|
+ $$ = (Node *)n;
|
|
+ }
|
|
+ | PARAM
|
|
+ {
|
|
+ Param *n = makeNode(Param);
|
|
+ n->paramkind = PARAM_NUM;
|
|
+ n->paramid = $1;
|
|
+ n->paramtype = INT4OID;
|
|
+ $$ = (Node *)n;
|
|
+ }
|
|
+ ;
|
|
+
|
|
+ select_offset_value: Iconst
|
|
+ {
|
|
+ Const *n = makeNode(Const);
|
|
+
|
|
+ n->consttype = INT4OID;
|
|
+ n->constlen = sizeof(int4);
|
|
+ n->constvalue = (Datum)$1;
|
|
+ n->constisnull = FALSE;
|
|
+ n->constbyval = TRUE;
|
|
+ n->constisset = FALSE;
|
|
+ n->constiscast = FALSE;
|
|
+ $$ = (Node *)n;
|
|
+ }
|
|
+ | PARAM
|
|
+ {
|
|
+ Param *n = makeNode(Param);
|
|
+ n->paramkind = PARAM_NUM;
|
|
+ n->paramid = $1;
|
|
+ n->paramtype = INT4OID;
|
|
+ $$ = (Node *)n;
|
|
+ }
|
|
;
|
|
|
|
/*
|
|
diff -cr src.orig/backend/parser/keywords.c src/backend/parser/keywords.c
|
|
*** src.orig/backend/parser/keywords.c Fri Oct 16 11:53:42 1998
|
|
--- src/backend/parser/keywords.c Sun Oct 18 22:13:29 1998
|
|
***************
|
|
*** 128,133 ****
|
|
--- 128,134 ----
|
|
{"leading", LEADING},
|
|
{"left", LEFT},
|
|
{"like", LIKE},
|
|
+ {"limit", LIMIT},
|
|
{"listen", LISTEN},
|
|
{"load", LOAD},
|
|
{"local", LOCAL},
|
|
***************
|
|
*** 156,161 ****
|
|
--- 157,163 ----
|
|
{"null", NULL_P},
|
|
{"numeric", NUMERIC},
|
|
{"of", OF},
|
|
+ {"offset", OFFSET},
|
|
{"oids", OIDS},
|
|
{"old", CURRENT},
|
|
{"on", ON},
|
|
diff -cr src.orig/backend/rewrite/rewriteDefine.c src/backend/rewrite/rewriteDefine.c
|
|
*** src.orig/backend/rewrite/rewriteDefine.c Fri Oct 16 11:53:46 1998
|
|
--- src/backend/rewrite/rewriteDefine.c Fri Oct 16 13:48:55 1998
|
|
***************
|
|
*** 312,317 ****
|
|
--- 312,323 ----
|
|
heap_close(event_relation);
|
|
|
|
/*
|
|
+ * LIMIT in view is not supported
|
|
+ */
|
|
+ if (query->limitOffset != NULL || query->limitCount != NULL)
|
|
+ elog(ERROR, "LIMIT clause not supported in views");
|
|
+
|
|
+ /*
|
|
* ... and finally the rule must be named _RETviewname.
|
|
*/
|
|
sprintf(expected_name, "_RET%s", event_obj->relname);
|
|
diff -cr src.orig/backend/tcop/pquery.c src/backend/tcop/pquery.c
|
|
*** src.orig/backend/tcop/pquery.c Fri Oct 16 11:53:47 1998
|
|
--- src/backend/tcop/pquery.c Fri Oct 16 14:02:36 1998
|
|
***************
|
|
*** 40,46 ****
|
|
#include "commands/command.h"
|
|
|
|
static char *CreateOperationTag(int operationType);
|
|
! static void ProcessQueryDesc(QueryDesc *queryDesc);
|
|
|
|
|
|
/* ----------------------------------------------------------------
|
|
--- 40,46 ----
|
|
#include "commands/command.h"
|
|
|
|
static char *CreateOperationTag(int operationType);
|
|
! static void ProcessQueryDesc(QueryDesc *queryDesc, Node *limoffset, Node *limcount);
|
|
|
|
|
|
/* ----------------------------------------------------------------
|
|
***************
|
|
*** 205,211 ****
|
|
* ----------------------------------------------------------------
|
|
*/
|
|
static void
|
|
! ProcessQueryDesc(QueryDesc *queryDesc)
|
|
{
|
|
Query *parseTree;
|
|
Plan *plan;
|
|
--- 205,211 ----
|
|
* ----------------------------------------------------------------
|
|
*/
|
|
static void
|
|
! ProcessQueryDesc(QueryDesc *queryDesc, Node *limoffset, Node *limcount)
|
|
{
|
|
Query *parseTree;
|
|
Plan *plan;
|
|
***************
|
|
*** 330,336 ****
|
|
* actually run the plan..
|
|
* ----------------
|
|
*/
|
|
! ExecutorRun(queryDesc, state, EXEC_RUN, 0);
|
|
|
|
/* save infos for EndCommand */
|
|
UpdateCommandInfo(operation, state->es_lastoid, state->es_processed);
|
|
--- 330,336 ----
|
|
* actually run the plan..
|
|
* ----------------
|
|
*/
|
|
! ExecutorRun(queryDesc, state, EXEC_RUN, limoffset, limcount);
|
|
|
|
/* save infos for EndCommand */
|
|
UpdateCommandInfo(operation, state->es_lastoid, state->es_processed);
|
|
***************
|
|
*** 373,377 ****
|
|
print_plan(plan, parsetree);
|
|
}
|
|
else
|
|
! ProcessQueryDesc(queryDesc);
|
|
}
|
|
--- 373,377 ----
|
|
print_plan(plan, parsetree);
|
|
}
|
|
else
|
|
! ProcessQueryDesc(queryDesc, parsetree->limitOffset, parsetree->limitCount);
|
|
}
|
|
diff -cr src.orig/include/executor/executor.h src/include/executor/executor.h
|
|
*** src.orig/include/executor/executor.h Fri Oct 16 11:53:56 1998
|
|
--- src/include/executor/executor.h Fri Oct 16 12:04:17 1998
|
|
***************
|
|
*** 83,89 ****
|
|
* prototypes from functions in execMain.c
|
|
*/
|
|
extern TupleDesc ExecutorStart(QueryDesc *queryDesc, EState *estate);
|
|
! extern TupleTableSlot *ExecutorRun(QueryDesc *queryDesc, EState *estate, int feature, int count);
|
|
extern void ExecutorEnd(QueryDesc *queryDesc, EState *estate);
|
|
extern HeapTuple ExecConstraints(char *caller, Relation rel, HeapTuple tuple);
|
|
#ifdef QUERY_LIMIT
|
|
--- 83,89 ----
|
|
* prototypes from functions in execMain.c
|
|
*/
|
|
extern TupleDesc ExecutorStart(QueryDesc *queryDesc, EState *estate);
|
|
! extern TupleTableSlot *ExecutorRun(QueryDesc *queryDesc, EState *estate, int feature, Node *limoffset, Node *limcount);
|
|
extern void ExecutorEnd(QueryDesc *queryDesc, EState *estate);
|
|
extern HeapTuple ExecConstraints(char *caller, Relation rel, HeapTuple tuple);
|
|
#ifdef QUERY_LIMIT
|
|
|
|
From owner-pgsql-hackers@hub.org Thu Oct 22 13:12:34 1998
|
|
Received: from renoir.op.net (root@renoir.op.net [209.152.193.4])
|
|
by candle.pha.pa.us (8.9.0/8.9.0) with ESMTP id NAA01350
|
|
for <maillist@candle.pha.pa.us>; Thu, 22 Oct 1998 13:12:29 -0400 (EDT)
|
|
Received: from hub.org (majordom@hub.org [209.47.148.200]) by renoir.op.net (o1/$ Revision: 1.18 $) with ESMTP id MAA17808 for <maillist@candle.pha.pa.us>; Thu, 22 Oct 1998 12:35:22 -0400 (EDT)
|
|
Received: from localhost (majordom@localhost)
|
|
by hub.org (8.9.1/8.8.8) with SMTP id KAA14887;
|
|
Thu, 22 Oct 1998 10:49:09 -0400 (EDT)
|
|
(envelope-from owner-pgsql-hackers@hub.org)
|
|
Received: by hub.org (TLB v0.10a (1.23 tibbs 1997/01/09 00:29:32)); Thu, 22 Oct 1998 10:44:59 +0000 (EDT)
|
|
Received: (from majordom@localhost)
|
|
by hub.org (8.9.1/8.8.8) id KAA14445
|
|
for pgsql-hackers-outgoing; Thu, 22 Oct 1998 10:44:57 -0400 (EDT)
|
|
(envelope-from owner-pgsql-hackers@postgreSQL.org)
|
|
X-Authentication-Warning: hub.org: majordom set sender to owner-pgsql-hackers@postgreSQL.org using -f
|
|
Received: from dsh.de (firewall-user@neptun.sns-felb.debis.de [53.122.101.2])
|
|
by hub.org (8.9.1/8.8.8) with ESMTP id KAA14431
|
|
for <pgsql-hackers@postgreSQL.org>; Thu, 22 Oct 1998 10:44:47 -0400 (EDT)
|
|
(envelope-from wieck@sapserv.debis.de)
|
|
Received: by dsh.de; id QAA19394; Thu, 22 Oct 1998 16:43:42 +0200 (MET DST)
|
|
Received: from dshmail.dsh.de(53.47.15.3) by neptun.dsh.de via smap (3.2)
|
|
id xma017268; Thu, 22 Oct 98 16:39:44 +0200
|
|
Received: from mail1.hh1.dsh.de (mail1.hh1.dsh.de [53.47.9.5])
|
|
by dshmail.dsh.de (8.8.7/8.8.7) with ESMTP id QAA02988;
|
|
Thu, 22 Oct 1998 16:36:46 +0200 (MET DST)
|
|
Received: from mars.SAPserv.Hamburg.dsh.de (root@mail5.hh1.dsh.de [53.2.168.17])
|
|
by mail1.hh1.dsh.de (8.8.7/8.8.7) with SMTP id QAA19155;
|
|
Thu, 22 Oct 1998 16:39:10 +0200
|
|
Received: from orion.SAPserv.Hamburg.dsh.de
|
|
by mars.SAPserv.Hamburg.dsh.de with smtp
|
|
for <<maillist@candle.pha.pa.us>>
|
|
id m0zWJWL-000B5DC; Thu, 22 Oct 98 14:07 MET DST
|
|
Received: by orion.SAPserv.Hamburg.dsh.de
|
|
for maillist@candle.pha.pa.us
|
|
id m0zWM4W-000EBPC; Thu, 22 Oct 98 16:50 MET DST
|
|
Message-Id: <m0zWM4W-000EBPC@orion.SAPserv.Hamburg.dsh.de>
|
|
From: jwieck@debis.com (Jan Wieck)
|
|
Subject: Re: [HACKERS] psql's help (the LIMIT stuff)
|
|
To: maillist@candle.pha.pa.us (Bruce Momjian)
|
|
Date: Thu, 22 Oct 1998 16:50:40 +0200 (MET DST)
|
|
Cc: jwieck@debis.com, jose@sferacarta.com, pgsql-hackers@postgreSQL.org
|
|
Reply-To: jwieck@debis.com (Jan Wieck)
|
|
In-Reply-To: <199810221424.KAA20601@candle.pha.pa.us> from "Bruce Momjian" at Oct 22, 98 10:24:08 am
|
|
X-Mailer: ELM [version 2.4 PL25]
|
|
Content-Type: text
|
|
Sender: owner-pgsql-hackers@postgreSQL.org
|
|
Precedence: bulk
|
|
Status: ROr
|
|
|
|
>
|
|
> > > >
|
|
> > > > I hope the QUERY_LIMIT too.
|
|
> > >
|
|
> > > I still have that cnfify() possible fix to review for KQSO. Are you
|
|
> > > still thinking limit for 6.4 final, or a minor release after that?
|
|
> >
|
|
> > I posted the part that is the minimum applied to 6.4 to make
|
|
> > adding LIMIT later non-initdb earlier. Anyway, here it's
|
|
> > again.
|
|
>
|
|
> Already applied. I assume it is the same as the one I applied.
|
|
|
|
Seen, thanks. Your 'Applied' just arrived after I packed it
|
|
again. It's the same.
|
|
|
|
> We are close to final, and can easily put it in 6.4.1, which I am sure
|
|
> we will need, and if we split CVS trees, you'll have lots of minor
|
|
> versions to pick from. :-)
|
|
>
|
|
> Seems like it would be a nice minor release item, but the problem is
|
|
> that minor releases aren't tested as much as major ones. How confident
|
|
> are you in the code? What do others thing?
|
|
|
|
I regression tested it, and did additional tests in the
|
|
SPI/PL area. It works. It only touches the parser and the
|
|
executor. Rules, planner/optimizer just bypass the values in
|
|
the parsetree. The parser and the executor are parts of
|
|
Postgres I feel very familiar with (not so in the optimizer).
|
|
I trust in the code and would use it in a production
|
|
environment.
|
|
|
|
It's below.
|
|
|
|
|
|
Jan
|
|
|
|
--
|
|
|
|
#======================================================================#
|
|
# It's easier to get forgiveness for being wrong than for being right. #
|
|
# Let's break this rule - forgive me. #
|
|
#======================================== jwieck@debis.com (Jan Wieck) #
|
|
|
|
|
|
diff -cr src.orig/backend/commands/command.c src/backend/commands/command.c
|
|
*** src.orig/backend/commands/command.c Fri Oct 16 11:53:38 1998
|
|
--- src/backend/commands/command.c Fri Oct 16 12:56:44 1998
|
|
***************
|
|
*** 39,44 ****
|
|
--- 39,45 ----
|
|
#include "utils/mcxt.h"
|
|
#include "utils/portal.h"
|
|
#include "utils/syscache.h"
|
|
+ #include "string.h"
|
|
|
|
/* ----------------
|
|
* PortalExecutorHeapMemory stuff
|
|
***************
|
|
*** 101,106 ****
|
|
--- 102,108 ----
|
|
int feature;
|
|
QueryDesc *queryDesc;
|
|
MemoryContext context;
|
|
+ Const limcount;
|
|
|
|
/* ----------------
|
|
* sanity checks
|
|
***************
|
|
*** 113,118 ****
|
|
--- 115,134 ----
|
|
}
|
|
|
|
/* ----------------
|
|
+ * Create a const node from the given count value
|
|
+ * ----------------
|
|
+ */
|
|
+ memset(&limcount, 0, sizeof(limcount));
|
|
+ limcount.type = T_Const;
|
|
+ limcount.consttype = INT4OID;
|
|
+ limcount.constlen = sizeof(int4);
|
|
+ limcount.constvalue = (Datum)count;
|
|
+ limcount.constisnull = FALSE;
|
|
+ limcount.constbyval = TRUE;
|
|
+ limcount.constisset = FALSE;
|
|
+ limcount.constiscast = FALSE;
|
|
+
|
|
+ /* ----------------
|
|
* get the portal from the portal name
|
|
* ----------------
|
|
*/
|
|
***************
|
|
*** 176,182 ****
|
|
PortalExecutorHeapMemory = (MemoryContext)
|
|
PortalGetHeapMemory(portal);
|
|
|
|
! ExecutorRun(queryDesc, PortalGetState(portal), feature, count);
|
|
|
|
if (dest == None) /* MOVE */
|
|
pfree(queryDesc);
|
|
--- 192,198 ----
|
|
PortalExecutorHeapMemory = (MemoryContext)
|
|
PortalGetHeapMemory(portal);
|
|
|
|
! ExecutorRun(queryDesc, PortalGetState(portal), feature, (Node *)NULL, (Node *)&limcount);
|
|
|
|
if (dest == None) /* MOVE */
|
|
pfree(queryDesc);
|
|
diff -cr src.orig/backend/executor/execMain.c src/backend/executor/execMain.c
|
|
*** src.orig/backend/executor/execMain.c Fri Oct 16 11:53:38 1998
|
|
--- src/backend/executor/execMain.c Fri Oct 16 20:05:19 1998
|
|
***************
|
|
*** 64,69 ****
|
|
--- 64,70 ----
|
|
static void EndPlan(Plan *plan, EState *estate);
|
|
static TupleTableSlot *ExecutePlan(EState *estate, Plan *plan,
|
|
Query *parseTree, CmdType operation,
|
|
+ int offsetTuples,
|
|
int numberTuples, ScanDirection direction,
|
|
void (*printfunc) ());
|
|
static void ExecRetrieve(TupleTableSlot *slot, void (*printfunc) (),
|
|
***************
|
|
*** 163,169 ****
|
|
* ----------------------------------------------------------------
|
|
*/
|
|
TupleTableSlot *
|
|
! ExecutorRun(QueryDesc *queryDesc, EState *estate, int feature, int count)
|
|
{
|
|
CmdType operation;
|
|
Query *parseTree;
|
|
--- 164,170 ----
|
|
* ----------------------------------------------------------------
|
|
*/
|
|
TupleTableSlot *
|
|
! ExecutorRun(QueryDesc *queryDesc, EState *estate, int feature, Node *limoffset, Node *limcount)
|
|
{
|
|
CmdType operation;
|
|
Query *parseTree;
|
|
***************
|
|
*** 171,176 ****
|
|
--- 172,179 ----
|
|
TupleTableSlot *result;
|
|
CommandDest dest;
|
|
void (*destination) ();
|
|
+ int offset = 0;
|
|
+ int count = 0;
|
|
|
|
/******************
|
|
* sanity checks
|
|
***************
|
|
*** 191,196 ****
|
|
--- 194,289 ----
|
|
estate->es_processed = 0;
|
|
estate->es_lastoid = InvalidOid;
|
|
|
|
+ /******************
|
|
+ * if given get the offset of the LIMIT clause
|
|
+ ******************
|
|
+ */
|
|
+ if (limoffset != NULL)
|
|
+ {
|
|
+ Const *coffset;
|
|
+ Param *poffset;
|
|
+ ParamListInfo paramLI;
|
|
+ int i;
|
|
+
|
|
+ switch (nodeTag(limoffset))
|
|
+ {
|
|
+ case T_Const:
|
|
+ coffset = (Const *)limoffset;
|
|
+ offset = (int)(coffset->constvalue);
|
|
+ break;
|
|
+
|
|
+ case T_Param:
|
|
+ poffset = (Param *)limoffset;
|
|
+ paramLI = estate->es_param_list_info;
|
|
+
|
|
+ if (paramLI == NULL)
|
|
+ elog(ERROR, "parameter for limit offset not in executor state");
|
|
+ for (i = 0; paramLI[i].kind != PARAM_INVALID; i++)
|
|
+ {
|
|
+ if (paramLI[i].kind == PARAM_NUM && paramLI[i].id == poffset->paramid)
|
|
+ break;
|
|
+ }
|
|
+ if (paramLI[i].kind == PARAM_INVALID)
|
|
+ elog(ERROR, "parameter for limit offset not in executor state");
|
|
+ if (paramLI[i].isnull)
|
|
+ elog(ERROR, "limit offset cannot be NULL value");
|
|
+ offset = (int)(paramLI[i].value);
|
|
+
|
|
+ break;
|
|
+
|
|
+ default:
|
|
+ elog(ERROR, "unexpected node type %d as limit offset", nodeTag(limoffset));
|
|
+ }
|
|
+
|
|
+ if (offset < 0)
|
|
+ elog(ERROR, "limit offset cannot be negative");
|
|
+ }
|
|
+
|
|
+ /******************
|
|
+ * if given get the count of the LIMIT clause
|
|
+ ******************
|
|
+ */
|
|
+ if (limcount != NULL)
|
|
+ {
|
|
+ Const *ccount;
|
|
+ Param *pcount;
|
|
+ ParamListInfo paramLI;
|
|
+ int i;
|
|
+
|
|
+ switch (nodeTag(limcount))
|
|
+ {
|
|
+ case T_Const:
|
|
+ ccount = (Const *)limcount;
|
|
+ count = (int)(ccount->constvalue);
|
|
+ break;
|
|
+
|
|
+ case T_Param:
|
|
+ pcount = (Param *)limcount;
|
|
+ paramLI = estate->es_param_list_info;
|
|
+
|
|
+ if (paramLI == NULL)
|
|
+ elog(ERROR, "parameter for limit count not in executor state");
|
|
+ for (i = 0; paramLI[i].kind != PARAM_INVALID; i++)
|
|
+ {
|
|
+ if (paramLI[i].kind == PARAM_NUM && paramLI[i].id == pcount->paramid)
|
|
+ break;
|
|
+ }
|
|
+ if (paramLI[i].kind == PARAM_INVALID)
|
|
+ elog(ERROR, "parameter for limit count not in executor state");
|
|
+ if (paramLI[i].isnull)
|
|
+ elog(ERROR, "limit count cannot be NULL value");
|
|
+ count = (int)(paramLI[i].value);
|
|
+
|
|
+ break;
|
|
+
|
|
+ default:
|
|
+ elog(ERROR, "unexpected node type %d as limit count", nodeTag(limcount));
|
|
+ }
|
|
+
|
|
+ if (count < 0)
|
|
+ elog(ERROR, "limit count cannot be negative");
|
|
+ }
|
|
+
|
|
switch (feature)
|
|
{
|
|
|
|
***************
|
|
*** 199,205 ****
|
|
plan,
|
|
parseTree,
|
|
operation,
|
|
! ALL_TUPLES,
|
|
ForwardScanDirection,
|
|
destination);
|
|
break;
|
|
--- 292,299 ----
|
|
plan,
|
|
parseTree,
|
|
operation,
|
|
! offset,
|
|
! count,
|
|
ForwardScanDirection,
|
|
destination);
|
|
break;
|
|
***************
|
|
*** 208,213 ****
|
|
--- 302,308 ----
|
|
plan,
|
|
parseTree,
|
|
operation,
|
|
+ offset,
|
|
count,
|
|
ForwardScanDirection,
|
|
destination);
|
|
***************
|
|
*** 222,227 ****
|
|
--- 317,323 ----
|
|
plan,
|
|
parseTree,
|
|
operation,
|
|
+ offset,
|
|
count,
|
|
BackwardScanDirection,
|
|
destination);
|
|
***************
|
|
*** 237,242 ****
|
|
--- 333,339 ----
|
|
plan,
|
|
parseTree,
|
|
operation,
|
|
+ 0,
|
|
ONE_TUPLE,
|
|
ForwardScanDirection,
|
|
destination);
|
|
***************
|
|
*** 691,696 ****
|
|
--- 788,794 ----
|
|
Plan *plan,
|
|
Query *parseTree,
|
|
CmdType operation,
|
|
+ int offsetTuples,
|
|
int numberTuples,
|
|
ScanDirection direction,
|
|
void (*printfunc) ())
|
|
***************
|
|
*** 742,747 ****
|
|
--- 840,859 ----
|
|
{
|
|
result = NULL;
|
|
break;
|
|
+ }
|
|
+
|
|
+ /******************
|
|
+ * For now we completely execute the plan and skip
|
|
+ * result tuples if requested by LIMIT offset.
|
|
+ * Finally we should try to do it in deeper levels
|
|
+ * if possible (during index scan)
|
|
+ * - Jan
|
|
+ ******************
|
|
+ */
|
|
+ if (offsetTuples > 0)
|
|
+ {
|
|
+ --offsetTuples;
|
|
+ continue;
|
|
}
|
|
|
|
/******************
|
|
diff -cr src.orig/backend/executor/functions.c src/backend/executor/functions.c
|
|
*** src.orig/backend/executor/functions.c Fri Oct 16 11:53:38 1998
|
|
--- src/backend/executor/functions.c Fri Oct 16 19:01:02 1998
|
|
***************
|
|
*** 130,135 ****
|
|
--- 130,138 ----
|
|
None);
|
|
estate = CreateExecutorState();
|
|
|
|
+ if (queryTree->limitOffset != NULL || queryTree->limitCount != NULL)
|
|
+ elog(ERROR, "LIMIT clause from SQL functions not yet implemented");
|
|
+
|
|
if (nargs > 0)
|
|
{
|
|
int i;
|
|
***************
|
|
*** 200,206 ****
|
|
|
|
feature = (LAST_POSTQUEL_COMMAND(es)) ? EXEC_RETONE : EXEC_RUN;
|
|
|
|
! return ExecutorRun(es->qd, es->estate, feature, 0);
|
|
}
|
|
|
|
static void
|
|
--- 203,209 ----
|
|
|
|
feature = (LAST_POSTQUEL_COMMAND(es)) ? EXEC_RETONE : EXEC_RUN;
|
|
|
|
! return ExecutorRun(es->qd, es->estate, feature, (Node *)NULL, (Node *)NULL);
|
|
}
|
|
|
|
static void
|
|
diff -cr src.orig/backend/executor/spi.c src/backend/executor/spi.c
|
|
*** src.orig/backend/executor/spi.c Fri Oct 16 11:53:39 1998
|
|
--- src/backend/executor/spi.c Fri Oct 16 19:25:33 1998
|
|
***************
|
|
*** 791,796 ****
|
|
--- 791,798 ----
|
|
bool isRetrieveIntoRelation = false;
|
|
char *intoName = NULL;
|
|
int res;
|
|
+ Const tcount_const;
|
|
+ Node *count = NULL;
|
|
|
|
switch (operation)
|
|
{
|
|
***************
|
|
*** 825,830 ****
|
|
--- 827,865 ----
|
|
return SPI_ERROR_OPUNKNOWN;
|
|
}
|
|
|
|
+ /* ----------------
|
|
+ * Get the query LIMIT tuple count
|
|
+ * ----------------
|
|
+ */
|
|
+ if (parseTree->limitCount != NULL)
|
|
+ {
|
|
+ /* ----------------
|
|
+ * A limit clause in the parsetree overrides the
|
|
+ * tcount parameter
|
|
+ * ----------------
|
|
+ */
|
|
+ count = parseTree->limitCount;
|
|
+ }
|
|
+ else
|
|
+ {
|
|
+ /* ----------------
|
|
+ * No LIMIT clause in parsetree. Use a local Const node
|
|
+ * to put tcount into it
|
|
+ * ----------------
|
|
+ */
|
|
+ memset(&tcount_const, 0, sizeof(tcount_const));
|
|
+ tcount_const.type = T_Const;
|
|
+ tcount_const.consttype = INT4OID;
|
|
+ tcount_const.constlen = sizeof(int4);
|
|
+ tcount_const.constvalue = (Datum)tcount;
|
|
+ tcount_const.constisnull = FALSE;
|
|
+ tcount_const.constbyval = TRUE;
|
|
+ tcount_const.constisset = FALSE;
|
|
+ tcount_const.constiscast = FALSE;
|
|
+
|
|
+ count = (Node *)&tcount_const;
|
|
+ }
|
|
+
|
|
if (state == NULL) /* plan preparation */
|
|
return res;
|
|
#ifdef SPI_EXECUTOR_STATS
|
|
***************
|
|
*** 845,851 ****
|
|
return SPI_OK_CURSOR;
|
|
}
|
|
|
|
! ExecutorRun(queryDesc, state, EXEC_FOR, tcount);
|
|
|
|
_SPI_current->processed = state->es_processed;
|
|
if (operation == CMD_SELECT && queryDesc->dest == SPI)
|
|
--- 880,886 ----
|
|
return SPI_OK_CURSOR;
|
|
}
|
|
|
|
! ExecutorRun(queryDesc, state, EXEC_FOR, parseTree->limitOffset, count);
|
|
|
|
_SPI_current->processed = state->es_processed;
|
|
if (operation == CMD_SELECT && queryDesc->dest == SPI)
|
|
diff -cr src.orig/backend/parser/analyze.c src/backend/parser/analyze.c
|
|
*** src.orig/backend/parser/analyze.c Fri Oct 16 11:53:41 1998
|
|
--- src/backend/parser/analyze.c Fri Oct 16 13:29:27 1998
|
|
***************
|
|
*** 180,186 ****
|
|
--- 180,190 ----
|
|
|
|
case T_SelectStmt:
|
|
if (!((SelectStmt *) parseTree)->portalname)
|
|
+ {
|
|
result = transformSelectStmt(pstate, (SelectStmt *) parseTree);
|
|
+ result->limitOffset = ((SelectStmt *)parseTree)->limitOffset;
|
|
+ result->limitCount = ((SelectStmt *)parseTree)->limitCount;
|
|
+ }
|
|
else
|
|
result = transformCursorStmt(pstate, (SelectStmt *) parseTree);
|
|
break;
|
|
diff -cr src.orig/backend/parser/gram.y src/backend/parser/gram.y
|
|
*** src.orig/backend/parser/gram.y Fri Oct 16 11:53:42 1998
|
|
--- src/backend/parser/gram.y Sun Oct 18 22:20:36 1998
|
|
***************
|
|
*** 45,50 ****
|
|
--- 45,51 ----
|
|
#include "catalog/catname.h"
|
|
#include "utils/elog.h"
|
|
#include "access/xact.h"
|
|
+ #include "catalog/pg_type.h"
|
|
|
|
#ifdef MULTIBYTE
|
|
#include "mb/pg_wchar.h"
|
|
***************
|
|
*** 163,169 ****
|
|
sort_clause, sortby_list, index_params, index_list, name_list,
|
|
from_clause, from_list, opt_array_bounds, nest_array_bounds,
|
|
expr_list, attrs, res_target_list, res_target_list2,
|
|
! def_list, opt_indirection, group_clause, TriggerFuncArgs
|
|
|
|
%type <node> func_return
|
|
%type <boolean> set_opt
|
|
--- 164,171 ----
|
|
sort_clause, sortby_list, index_params, index_list, name_list,
|
|
from_clause, from_list, opt_array_bounds, nest_array_bounds,
|
|
expr_list, attrs, res_target_list, res_target_list2,
|
|
! def_list, opt_indirection, group_clause, TriggerFuncArgs,
|
|
! opt_select_limit
|
|
|
|
%type <node> func_return
|
|
%type <boolean> set_opt
|
|
***************
|
|
*** 192,197 ****
|
|
--- 194,201 ----
|
|
|
|
%type <ival> fetch_how_many
|
|
|
|
+ %type <node> select_limit_value select_offset_value
|
|
+
|
|
%type <list> OptSeqList
|
|
%type <defelt> OptSeqElem
|
|
|
|
***************
|
|
*** 267,273 ****
|
|
FALSE_P, FETCH, FLOAT, FOR, FOREIGN, FROM, FULL,
|
|
GRANT, GROUP, HAVING, HOUR_P,
|
|
IN, INNER_P, INSENSITIVE, INSERT, INTERVAL, INTO, IS,
|
|
! JOIN, KEY, LANGUAGE, LEADING, LEFT, LIKE, LOCAL,
|
|
MATCH, MINUTE_P, MONTH_P, NAMES,
|
|
NATIONAL, NATURAL, NCHAR, NEXT, NO, NOT, NULL_P, NUMERIC,
|
|
OF, ON, ONLY, OPTION, OR, ORDER, OUTER_P,
|
|
--- 271,277 ----
|
|
FALSE_P, FETCH, FLOAT, FOR, FOREIGN, FROM, FULL,
|
|
GRANT, GROUP, HAVING, HOUR_P,
|
|
IN, INNER_P, INSENSITIVE, INSERT, INTERVAL, INTO, IS,
|
|
! JOIN, KEY, LANGUAGE, LEADING, LEFT, LIKE, LIMIT, LOCAL,
|
|
MATCH, MINUTE_P, MONTH_P, NAMES,
|
|
NATIONAL, NATURAL, NCHAR, NEXT, NO, NOT, NULL_P, NUMERIC,
|
|
OF, ON, ONLY, OPTION, OR, ORDER, OUTER_P,
|
|
***************
|
|
*** 299,305 ****
|
|
INCREMENT, INDEX, INHERITS, INSTEAD, ISNULL,
|
|
LANCOMPILER, LISTEN, LOAD, LOCATION, LOCK_P, MAXVALUE, MINVALUE, MOVE,
|
|
NEW, NOCREATEDB, NOCREATEUSER, NONE, NOTHING, NOTIFY, NOTNULL,
|
|
! OIDS, OPERATOR, PASSWORD, PROCEDURAL,
|
|
RECIPE, RENAME, RESET, RETURNS, ROW, RULE,
|
|
SEQUENCE, SERIAL, SETOF, SHOW, START, STATEMENT, STDIN, STDOUT, TRUSTED,
|
|
UNLISTEN, UNTIL, VACUUM, VALID, VERBOSE, VERSION
|
|
--- 303,309 ----
|
|
INCREMENT, INDEX, INHERITS, INSTEAD, ISNULL,
|
|
LANCOMPILER, LISTEN, LOAD, LOCATION, LOCK_P, MAXVALUE, MINVALUE, MOVE,
|
|
NEW, NOCREATEDB, NOCREATEUSER, NONE, NOTHING, NOTIFY, NOTNULL,
|
|
! OFFSET, OIDS, OPERATOR, PASSWORD, PROCEDURAL,
|
|
RECIPE, RENAME, RESET, RETURNS, ROW, RULE,
|
|
SEQUENCE, SERIAL, SETOF, SHOW, START, STATEMENT, STDIN, STDOUT, TRUSTED,
|
|
UNLISTEN, UNTIL, VACUUM, VALID, VERBOSE, VERSION
|
|
***************
|
|
*** 2591,2596 ****
|
|
--- 2595,2601 ----
|
|
result from_clause where_clause
|
|
group_clause having_clause
|
|
union_clause sort_clause
|
|
+ opt_select_limit
|
|
{
|
|
SelectStmt *n = makeNode(SelectStmt);
|
|
n->unique = $2;
|
|
***************
|
|
*** 2602,2607 ****
|
|
--- 2607,2622 ----
|
|
n->havingClause = $8;
|
|
n->unionClause = $9;
|
|
n->sortClause = $10;
|
|
+ if ($11 != NIL)
|
|
+ {
|
|
+ n->limitOffset = nth(0, $11);
|
|
+ n->limitCount = nth(1, $11);
|
|
+ }
|
|
+ else
|
|
+ {
|
|
+ n->limitOffset = NULL;
|
|
+ n->limitCount = NULL;
|
|
+ }
|
|
$$ = (Node *)n;
|
|
}
|
|
;
|
|
***************
|
|
*** 2699,2704 ****
|
|
--- 2714,2794 ----
|
|
| ASC { $$ = "<"; }
|
|
| DESC { $$ = ">"; }
|
|
| /*EMPTY*/ { $$ = "<"; /*default*/ }
|
|
+ ;
|
|
+
|
|
+ opt_select_limit: LIMIT select_offset_value ',' select_limit_value
|
|
+ { $$ = lappend(lappend(NIL, $2), $4); }
|
|
+ | LIMIT select_limit_value OFFSET select_offset_value
|
|
+ { $$ = lappend(lappend(NIL, $4), $2); }
|
|
+ | LIMIT select_limit_value
|
|
+ { $$ = lappend(lappend(NIL, NULL), $2); }
|
|
+ | OFFSET select_offset_value LIMIT select_limit_value
|
|
+ { $$ = lappend(lappend(NIL, $2), $4); }
|
|
+ | OFFSET select_offset_value
|
|
+ { $$ = lappend(lappend(NIL, $2), NULL); }
|
|
+ | /* EMPTY */
|
|
+ { $$ = NIL; }
|
|
+ ;
|
|
+
|
|
+ select_limit_value: Iconst
|
|
+ {
|
|
+ Const *n = makeNode(Const);
|
|
+
|
|
+ if ($1 < 1)
|
|
+ elog(ERROR, "selection limit must be ALL or a positive integer value > 0");
|
|
+
|
|
+ n->consttype = INT4OID;
|
|
+ n->constlen = sizeof(int4);
|
|
+ n->constvalue = (Datum)$1;
|
|
+ n->constisnull = FALSE;
|
|
+ n->constbyval = TRUE;
|
|
+ n->constisset = FALSE;
|
|
+ n->constiscast = FALSE;
|
|
+ $$ = (Node *)n;
|
|
+ }
|
|
+ | ALL
|
|
+ {
|
|
+ Const *n = makeNode(Const);
|
|
+ n->consttype = INT4OID;
|
|
+ n->constlen = sizeof(int4);
|
|
+ n->constvalue = (Datum)0;
|
|
+ n->constisnull = FALSE;
|
|
+ n->constbyval = TRUE;
|
|
+ n->constisset = FALSE;
|
|
+ n->constiscast = FALSE;
|
|
+ $$ = (Node *)n;
|
|
+ }
|
|
+ | PARAM
|
|
+ {
|
|
+ Param *n = makeNode(Param);
|
|
+ n->paramkind = PARAM_NUM;
|
|
+ n->paramid = $1;
|
|
+ n->paramtype = INT4OID;
|
|
+ $$ = (Node *)n;
|
|
+ }
|
|
+ ;
|
|
+
|
|
+ select_offset_value: Iconst
|
|
+ {
|
|
+ Const *n = makeNode(Const);
|
|
+
|
|
+ n->consttype = INT4OID;
|
|
+ n->constlen = sizeof(int4);
|
|
+ n->constvalue = (Datum)$1;
|
|
+ n->constisnull = FALSE;
|
|
+ n->constbyval = TRUE;
|
|
+ n->constisset = FALSE;
|
|
+ n->constiscast = FALSE;
|
|
+ $$ = (Node *)n;
|
|
+ }
|
|
+ | PARAM
|
|
+ {
|
|
+ Param *n = makeNode(Param);
|
|
+ n->paramkind = PARAM_NUM;
|
|
+ n->paramid = $1;
|
|
+ n->paramtype = INT4OID;
|
|
+ $$ = (Node *)n;
|
|
+ }
|
|
;
|
|
|
|
/*
|
|
diff -cr src.orig/backend/parser/keywords.c src/backend/parser/keywords.c
|
|
*** src.orig/backend/parser/keywords.c Fri Oct 16 11:53:42 1998
|
|
--- src/backend/parser/keywords.c Sun Oct 18 22:13:29 1998
|
|
***************
|
|
*** 128,133 ****
|
|
--- 128,134 ----
|
|
{"leading", LEADING},
|
|
{"left", LEFT},
|
|
{"like", LIKE},
|
|
+ {"limit", LIMIT},
|
|
{"listen", LISTEN},
|
|
{"load", LOAD},
|
|
{"local", LOCAL},
|
|
***************
|
|
*** 156,161 ****
|
|
--- 157,163 ----
|
|
{"null", NULL_P},
|
|
{"numeric", NUMERIC},
|
|
{"of", OF},
|
|
+ {"offset", OFFSET},
|
|
{"oids", OIDS},
|
|
{"old", CURRENT},
|
|
{"on", ON},
|
|
diff -cr src.orig/backend/rewrite/rewriteDefine.c src/backend/rewrite/rewriteDefine.c
|
|
*** src.orig/backend/rewrite/rewriteDefine.c Fri Oct 16 11:53:46 1998
|
|
--- src/backend/rewrite/rewriteDefine.c Fri Oct 16 13:48:55 1998
|
|
***************
|
|
*** 312,317 ****
|
|
--- 312,323 ----
|
|
heap_close(event_relation);
|
|
|
|
/*
|
|
+ * LIMIT in view is not supported
|
|
+ */
|
|
+ if (query->limitOffset != NULL || query->limitCount != NULL)
|
|
+ elog(ERROR, "LIMIT clause not supported in views");
|
|
+
|
|
+ /*
|
|
* ... and finally the rule must be named _RETviewname.
|
|
*/
|
|
sprintf(expected_name, "_RET%s", event_obj->relname);
|
|
diff -cr src.orig/backend/tcop/pquery.c src/backend/tcop/pquery.c
|
|
*** src.orig/backend/tcop/pquery.c Fri Oct 16 11:53:47 1998
|
|
--- src/backend/tcop/pquery.c Fri Oct 16 14:02:36 1998
|
|
***************
|
|
*** 40,46 ****
|
|
#include "commands/command.h"
|
|
|
|
static char *CreateOperationTag(int operationType);
|
|
! static void ProcessQueryDesc(QueryDesc *queryDesc);
|
|
|
|
|
|
/* ----------------------------------------------------------------
|
|
--- 40,46 ----
|
|
#include "commands/command.h"
|
|
|
|
static char *CreateOperationTag(int operationType);
|
|
! static void ProcessQueryDesc(QueryDesc *queryDesc, Node *limoffset, Node *limcount);
|
|
|
|
|
|
/* ----------------------------------------------------------------
|
|
***************
|
|
*** 205,211 ****
|
|
* ----------------------------------------------------------------
|
|
*/
|
|
static void
|
|
! ProcessQueryDesc(QueryDesc *queryDesc)
|
|
{
|
|
Query *parseTree;
|
|
Plan *plan;
|
|
--- 205,211 ----
|
|
* ----------------------------------------------------------------
|
|
*/
|
|
static void
|
|
! ProcessQueryDesc(QueryDesc *queryDesc, Node *limoffset, Node *limcount)
|
|
{
|
|
Query *parseTree;
|
|
Plan *plan;
|
|
***************
|
|
*** 330,336 ****
|
|
* actually run the plan..
|
|
* ----------------
|
|
*/
|
|
! ExecutorRun(queryDesc, state, EXEC_RUN, 0);
|
|
|
|
/* save infos for EndCommand */
|
|
UpdateCommandInfo(operation, state->es_lastoid, state->es_processed);
|
|
--- 330,336 ----
|
|
* actually run the plan..
|
|
* ----------------
|
|
*/
|
|
! ExecutorRun(queryDesc, state, EXEC_RUN, limoffset, limcount);
|
|
|
|
/* save infos for EndCommand */
|
|
UpdateCommandInfo(operation, state->es_lastoid, state->es_processed);
|
|
***************
|
|
*** 373,377 ****
|
|
print_plan(plan, parsetree);
|
|
}
|
|
else
|
|
! ProcessQueryDesc(queryDesc);
|
|
}
|
|
--- 373,377 ----
|
|
print_plan(plan, parsetree);
|
|
}
|
|
else
|
|
! ProcessQueryDesc(queryDesc, parsetree->limitOffset, parsetree->limitCount);
|
|
}
|
|
diff -cr src.orig/include/executor/executor.h src/include/executor/executor.h
|
|
*** src.orig/include/executor/executor.h Fri Oct 16 11:53:56 1998
|
|
--- src/include/executor/executor.h Fri Oct 16 12:04:17 1998
|
|
***************
|
|
*** 83,89 ****
|
|
* prototypes from functions in execMain.c
|
|
*/
|
|
extern TupleDesc ExecutorStart(QueryDesc *queryDesc, EState *estate);
|
|
! extern TupleTableSlot *ExecutorRun(QueryDesc *queryDesc, EState *estate, int feature, int count);
|
|
extern void ExecutorEnd(QueryDesc *queryDesc, EState *estate);
|
|
extern HeapTuple ExecConstraints(char *caller, Relation rel, HeapTuple tuple);
|
|
#ifdef QUERY_LIMIT
|
|
--- 83,89 ----
|
|
* prototypes from functions in execMain.c
|
|
*/
|
|
extern TupleDesc ExecutorStart(QueryDesc *queryDesc, EState *estate);
|
|
! extern TupleTableSlot *ExecutorRun(QueryDesc *queryDesc, EState *estate, int feature, Node *limoffset, Node *limcount);
|
|
extern void ExecutorEnd(QueryDesc *queryDesc, EState *estate);
|
|
extern HeapTuple ExecConstraints(char *caller, Relation rel, HeapTuple tuple);
|
|
#ifdef QUERY_LIMIT
|
|
|
|
|