Re: VERY slow queries at random

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On Thu, 7 Jun 2007, Gunther Mayer wrote:

wal checkpoint config is on pg defaults everywhere, all relevant config options are commented out. I'm no expert in wal stuff but I don't see how that could cause the problem?

Checkpoints are very resource intensive and can cause other processes (including your selects) to hang for a considerable period of time while they are processing. With the default parameters, they can happen very frequently. Normally checkpoint_segments and checkpoint_timeout are increased in order to keep this from happening.

This would normally be an issue only if you're writing a substantial amount of data to your tables. If there are a lot of writes going on, you might get some improvement by adjusting those parameters upward; the defaults are pretty low. Make sure you read http://www.postgresql.org/docs/8.2/static/wal-configuration.html first so you know what you're playing with, there are some recovery implications invoved.

--
* Greg Smith gsmith@xxxxxxxxxxxxx http://www.gregsmith.com Baltimore, MD


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