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Re: Queries sometimes take 1000 times the normal time

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: "Anders K(dot) Pedersen" <akp(at)cohaesio(dot)com>
Cc: pgsql-performance(at)postgresql(dot)org
Subject: Re: Queries sometimes take 1000 times the normal time
Date: 2003-08-27 23:39:08
Message-ID: (view raw, whole thread or download thread mbox)
Lists: pgsql-performance
"Anders K. Pedersen" <akp(at)cohaesio(dot)com> writes:
> Currently there's only a few users in the database for testing purposes, 
> and most of the time the user lookup's take 2-3 ms (I have syslog'ing of 
> queries and duration turned on), but several times per hour the duration 
> for one of the queries is 2-3 seconds (1000 times larger), while the 
> surrounding lookups take the usual 2-3 ms.

One thing that comes to mind is that the slow query could be occurring
at the same time as a checkpoint, or some other cycle-chewing background
operation.  It's not clear why a checkpoint would slow things down that
much, though.  Anyway I'd suggest looking for such activities; once we
know if that's the issue or not, we can make some progress.

			regards, tom lane

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