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Re: Query performance. 7.2.3 Vs. 7.3

From: Neil Conway <neilc(at)samurai(dot)com>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
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 02:38:59
Message-ID: 1038537539.379.61.camel@tokyo (view raw or flat)
Thread:
Lists: pgsql-hackers
On Thu, 2002-11-28 at 21:23, Tom Lane wrote:
> wade <wade(at)wavefire(dot)com> writes:
> > Explain output can be found at http://arch.wavefire.com/72v73a.txt
> 
> The difference evidently is that 7.3 chooses a mergejoin where 7.2
> picks a hashjoin.

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;').

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

Cheers,

Neil
-- 
Neil Conway <neilc(at)samurai(dot)com> || PGP Key ID: DB3C29FC




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