Re: Queries sometimes take 1000 times the normal time

Tom Lane wrote:
> "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.

One of my colleagues suggested looking for checkpoints as well; I
searched the log, but only the following messages turned up:

Aug 11 15:21:04 gs1 postgres[5447]: [2] LOG: checkpoint record is at
0/80193C
Aug 23 13:59:51 gs1 postgres[16451]: [2] LOG: checkpoint record is at
0/201EB74
Aug 25 02:48:17 gs1 postgres[1059]: [2] LOG: checkpoint record is at
0/2B787D0

Currently there are only relatively few changes to the database - one
INSERT everytime one of our game admins executes an administrative
command (like ban or kick), and this happens at most 10 times per hour.
As I understand checkpoints, this should mean, that they aren't
happening very often, and when they do, should be able to finish almost
immediately.

Regards,
Anders K. Pedersen