Add to optimizer file.
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Bruce Momjian
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@ -1059,7 +1059,7 @@ From owner-pgsql-hackers@hub.org Thu Jan 20 18:45:32 2000
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Thu, 20 Jan 2000 19:35:19 -0500 (EST)
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@ -1837,3 +1837,86 @@ what's left. I forget the figures exactly.
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Jules
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Jules
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From pgsql-hackers-owner+M6154@hub.org Wed Aug 23 14:36:41 2000
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Date: Wed, 23 Aug 2000 18:22:40 +0100 (WEST)
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From: =?iso-8859-1?Q?Tiago_Ant=E3o?= <tra@fct.unl.pt>
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To: Tom Lane <tgl@sss.pgh.pa.us>
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PostgreSQL Hackers list <pgsql-hackers@hub.org>
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Subject: Re: [HACKERS] analyze.c
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Status: ORr
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On Wed, 23 Aug 2000, Tom Lane wrote:
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> > What's the big reason not to do that? I know that
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> > there is some code in analyze.c (like comparing) that uses other parts of
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> > pg, but that seems to be easily fixed.
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>
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> Are you proposing not to do any comparisons? It will be interesting to
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> see how you can compute a histogram without any idea of equality or
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> ordering. But if you want that, then you still need the function-call
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> manager as well as the type-specific comparison routines for every
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> datatype that you might be asked to operate on (don't forget
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> user-defined types here).
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I forgot user defined data types :-(, but regarding histograms I think
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the code can be made external (at least for testing purposes):
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1. I was not suggesting not to do any comparisons, but I think the only
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comparison I need is equality, I don't need order as I don't need to
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calculate mins or maxs (I just need mins and maxes on frequencies, NOT on
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dat itself) to make a histogram.
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2. The mapping to text guarantees that I have (PQgetvalue returns
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always char* and pg_statistics keeps a "text" anyway) a way of knowing
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about equality regardless of type.
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But at least anything relating to order has to be in.
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> > I'm leaning toward the implementation of end-biased histograms. There is
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> > an introductory reference in the IEEE Data Engineering Bulletin, september
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> > 1995 (available on microsoft research site).
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>
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> Sounds interesting. Can you give us an exact URL?
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http://www.research.microsoft.com/research/db/debull/default.htm
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BTW, you can get access to SIGMOD CDs with lots of goodies for a very low
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price (at least in 1999 it was a bargain), check out ACM membership for
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sigmod.
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I've been reading something about implementation of histograms, and,
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AFAIK, in practice histograms is just a cool name for no more than:
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1. top ten with frequency for each
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2. the same for top ten worse
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3. average for the rest
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I'm writing code get this info (outside pg for now - for testing
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purposes).
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Best Regards,
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Tiago
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PS - again: I'm starting, so, some of my comments can be completly dumb.
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