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Re: Difference between explain analyze and real execution time

From: Artur Zając <azajac(at)ang(dot)com(dot)pl>
To: "'Robert Haas'" <robertmhaas(at)gmail(dot)com>
Cc: <pgsql-performance(at)postgresql(dot)org>
Subject: Re: Difference between explain analyze and real execution time
Date: 2010-11-15 20:43:48
Message-ID: 009d01cb8505$ce738900$6b5a9b00$@ang.com.pl (view raw or flat)
Thread:
Lists: pgsql-performance

2010/11/15 Artur Zając <azajac(at)ang(dot)com(dot)pl>:
> Why there is so big difference between explain analyze (0.710 ms) and 
> real execution time (3309 ms)? Any suggestions?

> Could it be that it takes a long time to plan for some reason?  How fast
is a plain EXPLAIN?

Yes! That is it :) Planning is painful. I'm so stupid. I didn't check VACUUM
without ANALYZE :)

time psql  -c 'explain SELECT te.idt FROM t_positions AS te    WHERE te.idtr
IN (347186)'

real    0m1.087s
user    0m0.004s
sys     0m0.001s

I've changed default_statistics_target to 10000 and I think that is a
reason. When I changed it to 1000 everything seems to be ok:

time psql  -c 'explain analyze SELECT te.idt FROM t_positions AS te    WHERE
te.idtr IN (347186)'

real    0m0.062s
user    0m0.003s
sys     0m0.004s

Thanks.

-------------------------------------------
Artur Zajac



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