Add to TODO.detail.
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Bruce Momjian
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@ -345,7 +345,7 @@ From owner-pgsql-hackers@hub.org Tue Oct 19 10:31:10 1999
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@ -454,7 +454,7 @@ From owner-pgsql-hackers@hub.org Tue Oct 19 21:25:30 1999
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@ -739,3 +739,266 @@ dirty one in LRU.
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Vadim
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From markw@mohawksoft.com Thu Jun 7 14:40:02 2001
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Message-ID: <3B1FC9CB.57C72AD6@mohawksoft.com>
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Date: Thu, 07 Jun 2001 14:36:59 -0400
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From: mlw <markw@mohawksoft.com>
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To: Bruce Momjian <pgman@candle.pha.pa.us>,
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"pgsql-hackers@postgresql.org" <pgsql-hackers@postgresql.org>
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Subject: Re: 7.2 items
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References: <200106071503.f57F32n03924@candle.pha.pa.us>
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Content-Type: text/plain; charset=us-ascii
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Content-Transfer-Encoding: 7bit
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Status: OR
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Bruce Momjian wrote:
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> > Bruce Momjian <pgman@candle.pha.pa.us> writes:
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> >
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> > > Here is a small list of big TODO items. I was wondering which ones
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> > > people were thinking about for 7.2?
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> >
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> > A friend of mine wants to use PostgreSQL instead of Oracle for a large
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> > application, but has run into a snag when speed comparisons looked
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> > good until the Oracle folks added a couple of BITMAP indexes. I can't
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> > recall seeing any discussion about that here -- are there any plans?
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>
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> It is not on our list and I am not sure what they do.
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Do you have access to any Oracle Documentation? There is a good explanation
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of them.
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However, I will try to explain.
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If you have a table, locations. It has 1,000,000 records.
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In oracle you do this:
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create bitmap index bitmap_foo on locations (state) ;
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For each unique value of 'state' oracle will create a bitmap with 1,000,000
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bits in it. With a one representing a match and a zero representing no
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match. Record '0' in the table is represented by bit '0' in the bitmap,
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record '1' is represented by bit '1', record two by bit '2' and so on.
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In a table where comparatively few different values are to be indexed in a
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large table, a bitmap index can be quite small and not suffer the N * log(N)
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disk I/O most tree based indexes suffer. If the bitmap is fairly sparse or
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dense (or have periods of denseness and sparseness), it can be compressed
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very efficiently as well.
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When the statement:
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select * from locations where state = 'MA';
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Is executed, the bitmap is read into memory in very few disk operations.
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(Perhaps even as few as one or two). It is a simple operation of rifling
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through the bitmap for '1's that indicate the record has the property,
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'state' = 'MA';
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From mascarm@mascari.com Thu Jun 7 15:36:25 2001
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Return-path: <mascarm@mascari.com>
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Received: from corvette.mascari.com (dhcp065-024-161-045.columbus.rr.com [65.24.161.45])
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Thu, 7 Jun 2001 15:29:31 -0400
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Received: by localhost with Microsoft MAPI; Thu, 7 Jun 2001 15:34:18 -0400
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Message-ID: <01C0EF67.5105D2E0.mascarm@mascari.com>
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From: Mike Mascari <mascarm@mascari.com>
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Reply-To: "mascarm@mascari.com" <mascarm@mascari.com>
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To: "'mlw'" <markw@mohawksoft.com>, Bruce Momjian <pgman@candle.pha.pa.us>,
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"pgsql-hackers@postgresql.org" <pgsql-hackers@postgresql.org>
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Subject: RE: [HACKERS] Re: 7.2 items
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Date: Thu, 7 Jun 2001 15:34:17 -0400
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Organization: Mascari Development Inc.
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X-Mailer: Microsoft Internet E-mail/MAPI - 8.0.0.4211
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Status: OR
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And in addition,
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If you submitted the query:
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SELECT * FROM addresses WHERE state = 'OH'
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AND areacode = '614'
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Then, with bitmap indexes, the bitmaps are just logically ANDed
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together, and the final bitmap determines the matching rows.
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Mike Mascari
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mascarm@mascari.com
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-----Original Message-----
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From: mlw [SMTP:markw@mohawksoft.com]
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Bruce Momjian wrote:
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> > Bruce Momjian <pgman@candle.pha.pa.us> writes:
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> >
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> > > Here is a small list of big TODO items. I was wondering which
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ones
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> > > people were thinking about for 7.2?
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> >
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> > A friend of mine wants to use PostgreSQL instead of Oracle for a
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large
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> > application, but has run into a snag when speed comparisons
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looked
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> > good until the Oracle folks added a couple of BITMAP indexes. I
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can't
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> > recall seeing any discussion about that here -- are there any
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plans?
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>
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> It is not on our list and I am not sure what they do.
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Do you have access to any Oracle Documentation? There is a good
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explanation
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of them.
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However, I will try to explain.
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If you have a table, locations. It has 1,000,000 records.
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In oracle you do this:
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create bitmap index bitmap_foo on locations (state) ;
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For each unique value of 'state' oracle will create a bitmap with
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1,000,000
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bits in it. With a one representing a match and a zero representing
|
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no
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match. Record '0' in the table is represented by bit '0' in the
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bitmap,
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record '1' is represented by bit '1', record two by bit '2' and so
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on.
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In a table where comparatively few different values are to be indexed
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in a
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large table, a bitmap index can be quite small and not suffer the N *
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log(N)
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disk I/O most tree based indexes suffer. If the bitmap is fairly
|
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sparse or
|
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dense (or have periods of denseness and sparseness), it can be
|
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compressed
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very efficiently as well.
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When the statement:
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select * from locations where state = 'MA';
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|
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Is executed, the bitmap is read into memory in very few disk
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operations.
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(Perhaps even as few as one or two). It is a simple operation of
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rifling
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through the bitmap for '1's that indicate the record has the
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property,
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'state' = 'MA';
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From oleg@sai.msu.su Thu Jun 7 15:39:15 2001
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Return-path: <oleg@sai.msu.su>
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Received: from ra.sai.msu.su (ra.sai.msu.su [158.250.29.2])
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by candle.pha.pa.us (8.10.1/8.10.1) with ESMTP id f57Jd7c22010
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for <pgman@candle.pha.pa.us>; Thu, 7 Jun 2001 15:39:08 -0400 (EDT)
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Received: from ra (ra [158.250.29.2])
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Thu, 7 Jun 2001 22:38:20 +0300 (GMT)
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Date: Thu, 7 Jun 2001 22:38:20 +0300 (GMT)
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From: Oleg Bartunov <oleg@sai.msu.su>
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X-X-Sender: <megera@ra.sai.msu.su>
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To: mlw <markw@mohawksoft.com>
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cc: Bruce Momjian <pgman@candle.pha.pa.us>,
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"pgsql-hackers@postgresql.org" <pgsql-hackers@postgresql.org>
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Subject: Re: [HACKERS] Re: 7.2 items
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In-Reply-To: <3B1FC9CB.57C72AD6@mohawksoft.com>
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Message-ID: <Pine.GSO.4.33.0106072234120.6015-100000@ra.sai.msu.su>
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MIME-Version: 1.0
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Content-Type: TEXT/PLAIN; charset=US-ASCII
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Status: OR
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I think it's possible to implement bitmap indexes with a little
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effort using GiST. at least I know one implementation
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http://www.it.iitb.ernet.in/~rvijay/dbms/proj/
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if you have interests you could implement bitmap indexes yourself
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unfortunately, we're very busy
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Oleg
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On Thu, 7 Jun 2001, mlw wrote:
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> Bruce Momjian wrote:
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>
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> > > Bruce Momjian <pgman@candle.pha.pa.us> writes:
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> > >
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> > > > Here is a small list of big TODO items. I was wondering which ones
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> > > > people were thinking about for 7.2?
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> > >
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> > > A friend of mine wants to use PostgreSQL instead of Oracle for a large
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> > > application, but has run into a snag when speed comparisons looked
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> > > good until the Oracle folks added a couple of BITMAP indexes. I can't
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> > > recall seeing any discussion about that here -- are there any plans?
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> >
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> > It is not on our list and I am not sure what they do.
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>
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> Do you have access to any Oracle Documentation? There is a good explanation
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> of them.
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>
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> However, I will try to explain.
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>
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> If you have a table, locations. It has 1,000,000 records.
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>
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> In oracle you do this:
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>
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> create bitmap index bitmap_foo on locations (state) ;
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>
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> For each unique value of 'state' oracle will create a bitmap with 1,000,000
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> bits in it. With a one representing a match and a zero representing no
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> match. Record '0' in the table is represented by bit '0' in the bitmap,
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> record '1' is represented by bit '1', record two by bit '2' and so on.
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>
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> In a table where comparatively few different values are to be indexed in a
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> large table, a bitmap index can be quite small and not suffer the N * log(N)
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> disk I/O most tree based indexes suffer. If the bitmap is fairly sparse or
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> dense (or have periods of denseness and sparseness), it can be compressed
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> very efficiently as well.
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>
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> When the statement:
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>
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> select * from locations where state = 'MA';
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>
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> Is executed, the bitmap is read into memory in very few disk operations.
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> (Perhaps even as few as one or two). It is a simple operation of rifling
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> through the bitmap for '1's that indicate the record has the property,
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> 'state' = 'MA';
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>
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>
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> ---------------------------(end of broadcast)---------------------------
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> TIP 6: Have you searched our list archives?
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>
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> http://www.postgresql.org/search.mpl
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>
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Regards,
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Oleg
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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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