From: Brad Nicholson <bnichols@ca.afilias.info>
To: pgsql-performance@postgresql.org
Subject: 7.4 Checkpoint Question
Date: Thu, 29 Nov 2007 10:10:54 -0500
Message-ID: <1196349054.5651.19.camel@bnicholson-desktop> (raw)
I have a legacy system still on 7.4 (I know, I know...the upgrade is
coming soon).
I have a fairly big spike happening once a day, every day, at the same
time. It happens during a checkpoint, no surprise there. I know the
solution to the problem (upgrade to a modern version), but what I'm
looking for as an explanation as to why one particular checkpoint would
be so bad on a low volume system, so I can appease certain management
concerns.
This is a _really _low volume system, less than 500 writes/hour. Normal
operation sees checkpoint related spikes of around 200-300 milliseconds.
We always checkpoint at the checkpoint timeout (every 5 minutes).
During this one checkpoint, I'm seeing transactions running 2-3 seconds.
During this time, writes are < 5/minute.
Relevant settings:
shared_buffers = 10000
checkpoint_segments = 30
checkpoint_timeout = 300
What gives?
--
Brad Nicholson 416-673-4106
Database Administrator, Afilias Canada Corp.
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To: pgsql-performance@postgresql.org
Cc: bnichols@ca.afilias.info
Subject: Re: 7.4 Checkpoint Question
In-Reply-To: <1196349054.5651.19.camel@bnicholson-desktop>
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