From: Mindaugas Riauba <mind@bi.lt>
To: Cosimo Streppone <cosimo@streppone.it>
Cc: pgsql-performance@postgresql.org
Subject: Re: PostgreSQL strugling during high load
Date: Fri, 13 May 2005 18:41:43 +0300
Message-ID: <02f901c557d2$43517e10$f20214ac@bite.lt> (raw)
References: <01cc01c557ba$a4fdb0b0$f20214ac@bite.lt>
<23217.1115991763@sss.pgh.pa.us>
<022901c557c5$73df1220$f20214ac@bite.lt>
<4284C661.4050406@streppone.it>
> >>The "vacuum cost" parameters can be adjusted to make vacuums fired
> >>by pg_autovacuum less of a burden. I haven't got any specific numbers
> >>to suggest, but perhaps someone else does.
> >
> > It looks like that not only vacuum causes our problems. vacuum_cost
> > seems to lower vacuum impact but we are still noticing slow queries
"storm".
> > We are logging queries that takes >2000ms to process.
> > And there is quiet periods and then suddenly 30+ slow queries appears
in
> > log within the same second. What else could cause such behaviour?
>
> I've seen that happen when you're placing (explicitly or
> *implicitly*) locks on the records you're trying to update/delete.
>
> If you're willing to investigate, `pg_locks' system view holds
> information about db locks.
Hm. Yes. Number of locks varies quite alot (10-600). Now what to
investigate
further? We do not use explicit locks in our functions. We use quite simple
update/delete where key=something;
Some sample (select * from pg_locks order by pid) is below.
Thanks,
Mindaugas
| | 584302172 | 11836 | ExclusiveLock | t
17236 | 17230 | | 11836 | AccessShareLock | t
17236 | 17230 | | 11836 | RowExclusiveLock | t
127103 | 17230 | | 11836 | RowExclusiveLock | t
127106 | 17230 | | 11836 | RowExclusiveLock | t
127109 | 17230 | | 11836 | AccessShareLock | t
127109 | 17230 | | 11836 | RowExclusiveLock | t
127109 | 17230 | | 11837 | AccessShareLock | t
127109 | 17230 | | 11837 | RowExclusiveLock | t
17236 | 17230 | | 11837 | AccessShareLock | t
17236 | 17230 | | 11837 | RowExclusiveLock | t
127106 | 17230 | | 11837 | RowExclusiveLock | t
127103 | 17230 | | 11837 | RowExclusiveLock | t
| | 584302173 | 11837 | ExclusiveLock | t
127103 | 17230 | | 11838 | RowExclusiveLock | t
17236 | 17230 | | 11838 | RowExclusiveLock | t
127109 | 17230 | | 11838 | RowExclusiveLock | t
| | 584302174 | 11838 | ExclusiveLock | t
17285 | 17230 | | 11838 | AccessShareLock | t
17251 | 17230 | | 11838 | AccessShareLock | t
130516 | 17230 | | 11838 | AccessShareLock | t
127106 | 17230 | | 11838 | RowExclusiveLock | t
17278 | 17230 | | 11838 | AccessShareLock | t
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To: pgsql-performance@postgresql.org
Cc: mind@bi.lt, cosimo@streppone.it
Subject: Re: PostgreSQL strugling during high load
In-Reply-To: <02f901c557d2$43517e10$f20214ac@bite.lt>
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