От: Tom Lane
Тема: Re: Slow INSERT
Дата: ,
Msg-id: 29835.1088522568@sss.pgh.pa.us
(см: обсуждение, исходный текст)
Ответ на: Re: Slow INSERT  (Michal Taborsky)
Список: pgsql-performance

Скрыть дерево обсуждения

Slow INSERT  (Michal Táborský, )
 Re: Slow INSERT  (Tom Lane, )
  Re: Slow INSERT  (Michal Taborsky, )
   Re: Slow INSERT  (Tom Lane, )
 Re: Slow INSERT  (Michal Taborsky, )
  Re: Slow INSERT  (Tom Lane, )

Michal Taborsky <> writes:
> I ran some tests to support this hypothesis. Every 500th insert is a tad
> slower, but it is insignificant (normally the INSERT lasts 1.5ms, every
> 500th is 9ms). During my tests (10 runs of 1000 INSERTS) I had
> experienced only one "slow" insert (2000ms). It is clearly caused by
> other processes running on this server, but such degradation of
> performance is highly suspicious, because the server very rarely goes
> over load 1.0.

Actually, the simpler theory is that the slowdown is caused by
background checkpoint operations.  Now a checkpoint would slow
*everything* down not only this one insert, so maybe that's not
the right answer either, but it's my next idea.  You could check
this to some extent by manually issuing a CHECKPOINT command and
seeing if you get an insert hiccup.  Note though that closely
spaced checkpoints will have less effect, because less I/O will
be triggered when not much has changed since the last one.  So
you'd want to wait a bit between experiments.

            regards, tom lane


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