Scott Rankin <[email protected]> writes:
> Iâm trying to track down why some queries on my database system are
> intermittently much slower than usual. I have some queries that run, on
> average, 2-3ms, and they run at a rate of about 10-20 queries/second.
> However, every 3-5 seconds, one of the queries will be 500-100ms. This is
> making the average query time turn out to be closer to 20ms, with a very
> large standard deviation.
> This happens to a number of otherwise very fast queries, and Iâm trying to
> trace the reason. Iâve turned on lock logging and checkpoint logging, and
> this behavior happens whether or not a checkpoint is occurring. There are no
> lock waits happening in the system either.
I doubt you've proved that --- log_lock_waits will only report on waits
longer than deadlock_timeout, which you don't appear to have changed from
its default of 1 sec. If you're trying to capture events that last a few
hundred msec, you're going to need to reduce deadlock_timeout to maybe
100ms.
It would help to know more about what the queries are, too. The cause
might be something like GIN index pending-list cleanup but we can't tell
on the basis of this much info.
regards, tom lane
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