From: Tom Lane <tgl@sss.pgh.pa.us>
To: Mark Kirkwood <mark.kirkwood@catalyst.net.nz>
Cc: PGSQL Performance <pgsql-performance@postgresql.org>
Subject: Re: 8.4 optimization regression?
Date: Thu, 01 Sep 2011 19:13:56 -0400
Message-ID: <26940.1314918836@sss.pgh.pa.us> (raw)
In-Reply-To: <5156.1314829311@sss.pgh.pa.us>
References: <4E5331FF.3000900@catalyst.net.nz>
<15708.1314155740@sss.pgh.pa.us>
<4E5DCFA4.5090806@catalyst.net.nz>
<5156.1314829311@sss.pgh.pa.us>
I wrote:
> Mark Kirkwood <mark.kirkwood@catalyst.net.nz> writes:
>> [ assorted examples showing that commit
>> 7f3eba30c9d622d1981b1368f2d79ba0999cdff2 has got problems ]
> ...
> So, not only are you correct that we should revert the changes to
> eqjoinsel_inner, but what's happening in eqjoinsel_semi is wrong too.
I've retested these examples with the patches I committed yesterday.
Six of the eight examples are estimated pretty nearly dead on, while the
other two are estimated about 50% too high (still a lot better than
before). AFAICT there's no easy way to improve those estimates further;
eqjoinsel_semi just plain hasn't got enough information to know how many
matches there will be.
regards, tom lane
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To: pgsql-performance@postgresql.org
Cc: tgl@sss.pgh.pa.us, mark.kirkwood@catalyst.net.nz
Subject: Re: 8.4 optimization regression?
In-Reply-To: <26940.1314918836@sss.pgh.pa.us>
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