Re: Possible regression (slow query on 9.2/9.3 when compared to 9.1)

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Ronaldo Maia <romaia(at)async(dot)com(dot)br>
Cc: pgsql-performance(at)postgresql(dot)org
Subject: Re: Possible regression (slow query on 9.2/9.3 when compared to 9.1)
Date: 2013-12-29 22:32:20
Message-ID: 30316.1388356340@sss.pgh.pa.us
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Ronaldo Maia <romaia(at)async(dot)com(dot)br> writes:
> Recently I have tried to upgrade our postgres instalation from 9.1 to 9.3,
> but one query in particular got extremelly slow.

FWIW, this test case doesn't reproduce any problem for me --- I get
identical plans and indistinguishable timings (about 450ms on my machine)
from 9.1 and 9.3 branch tips. This is with all-default settings and
a VACUUM ANALYZE after loading the data. I had to guess at the definition
of stoq_normalize_string(), too, so I used

create function stoq_normalize_string(text) returns text language sql
strict immutable as 'select unaccent($1)';

I speculate that you forgot to analyze the data after loading, or there's
some performance-relevant setting that you didn't carry forward from the
9.1 database.

regards, tom lane

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