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Re: Query performance. 7.2.3 Vs. 7.3

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Neil Conway <neilc(at)samurai(dot)com>
Cc: wade <wade(at)wavefire(dot)com>, pgsql-hackers(at)postgresql(dot)org
Subject: Re: Query performance. 7.2.3 Vs. 7.3
Date: 2002-11-29 02:58:14
Message-ID: (view raw, whole thread or download thread mbox)
Lists: pgsql-hackers
Neil Conway <neilc(at)samurai(dot)com> writes:
> I was looking at this a bit in IRC, and I was more concerned by the fact
> that 7.3 was 20% than 7.2 on the same hardware, when they both used the
> same query plan (consider the data at the end of the URL above, after
> the execution of 'SET enable_mergejoin = off;').

Hm.  Are we sure that both versions were built with the same
optimization level, etc?  (My private bet is that Wade's 7.2 didn't
have multibyte or locale support --- but that's a long shot when we
don't know the datatypes of the columns being joined on...)

> Also, is it expected that the cardinality estimates for join steps won't
> be very accurate, right? (estimated: 19 rows, actual: 765 rows)

Well, it'd be nice to do better --- I was hoping Wade would look into
why the row estimates were off so much.

			regards, tom lane

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