From: Tom Lane <tgl@sss.pgh.pa.us>
To: Tomas Vondra <tomas.vondra@2ndquadrant.com>
cc: pgsql-performance@postgresql.org
Subject: Re: Different plan for very similar queries
In-reply-to: <556B3160.2010706@2ndquadrant.com>
References: <20150529085544.GA15813@hjp.at> <20150529095117.GB15813@hjp.at>
 <5568FAA5.3080807@2ndquadrant.com> <29819.1433012674@sss.pgh.pa.us>
 <20150531110010.GA25173@hjp.at> <556B3160.2010706@2ndquadrant.com>
Comments: In-reply-to Tomas Vondra <tomas.vondra@2ndquadrant.com>
 message dated "Sun, 31 May 2015 18:05:52 +0200"
Date: Sun, 31 May 2015 12:22:32 -0400
Message-ID: <633.1433089352@sss.pgh.pa.us>
Precedence: bulk
Sender: pgsql-performance-owner@postgresql.org

Tomas Vondra <tomas.vondra@2ndquadrant.com> writes:
> On 05/31/15 13:00, Peter J. Holzer wrote:
>> (There was no analyze on facttable_stat_fta4 (automatic or manual) on
>> facttable_stat_fta4 between those two tests, so the statistics on
>> facttable_stat_fta4 shouldn't have changed - only those for term.)

> So maybe there was autoanalyze, because otherwise it really should be 
> the same in both plans ...

No, because that's the inside of a nestloop with significantly different
outer-side rowcount estimates.  The first case gets a benefit from the
expectation that it will be re-executed many times (see the impact of
loop_count on cost_index).

			regards, tom lane


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