Re: Different plan for very similar queries

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Tomas Vondra <tomas(dot)vondra(at)2ndquadrant(dot)com>
Cc: pgsql-performance(at)postgresql(dot)org
Subject: Re: Different plan for very similar queries
Date: 2015-05-31 16:22:32
Message-ID: 633.1433089352@sss.pgh.pa.us
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Tomas Vondra <tomas(dot)vondra(at)2ndquadrant(dot)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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