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Re: Slow update with simple query

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Arnaud Lesauvage <thewild(at)freesurf(dot)fr>
Cc: Ragnar <gnari(at)hive(dot)is>, Jens Schipkowski <jens(dot)schipkowski(at)apus(dot)co(dot)at>, pgsql-performance(at)postgresql(dot)org
Subject: Re: Slow update with simple query
Date: 2006-12-14 16:19:00
Message-ID: 21233.1166113140@sss.pgh.pa.us (view raw or flat)
Thread:
Lists: pgsql-performance
Arnaud Lesauvage <thewild(at)freesurf(dot)fr> writes:
> Tom Lane a crit :
>> It seems the time must be going into this trigger function.  What
>> does it do?

> A lot of things ! Indeed, if it runs it will very badly hurt performances (table 
> lookups, string manipulation, etc...) !
> But it should only be tringered on INSERTs, and I am doing an UPDATE !

Doh, right, I obviously still need to ingest more caffeine this morning.

I think the conclusion must be that there was just too much I/O to be
done to update all the rows.  Have you done any tuning of shared_buffers
and so forth?  I recall having seen cases where update performance went
bad as soon as the upper levels of a large index no longer fit into
shared_buffers ...

			regards, tom lane

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