From: Greg Smith <gsmith@gregsmith.com>
To: Gunther Mayer <gunther.mayer@googlemail.com>
Cc: pgsql-performance@postgresql.org
Subject: Re: VERY slow queries at random
Date: Thu, 7 Jun 2007 15:42:41 -0400 (EDT)
Message-ID: <Pine.GSO.4.64.0706071529380.2676@westnet.com> (raw)
In-Reply-To: <4668265D.2010200@gmail.com>
References: <46670916.9090505@gmail.com>
<466726D3.7050102@g2switchworks.com>
<D7DB4C26-9247-43DD-A765-E81CA0D71DFC@skype.net>
<4668265D.2010200@gmail.com>
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@gregsmith.com http://www.gregsmith.com Baltimore, MD
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To: pgsql-performance@postgresql.org
Cc: gsmith@gregsmith.com, gunther.mayer@googlemail.com
Subject: Re: VERY slow queries at random
In-Reply-To: <Pine.GSO.4.64.0706071529380.2676@westnet.com>
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