On Oct 5, 2005, at 8:23 AM, Ian Westmacott wrote:

Can anyone tell me what precisely a WAL buffer contains,
so that I can compute an appropriate setting for
wal_buffers (in 8.0.3)?

I know the documentation suggests there is little
evidence that supports increasing wal_buffers, but we
are inserting a large amount of data that, I believe,
easily exceeds the default 64K in a single transaction.
We are also very sensitive to write latency.

As background, we are doing a sustained insert of 2.2
billion rows in 1.3 million transactions per day.  Thats
about 1700 rows per transaction, at (roughly) 50 bytes
per row.

Ian,

The WAL Configuration chapter (25.2) has a pretty good discussion of how wal_buffers is used:

http://www.postgresql.org/docs/8.0/static/wal-configuration.html

You might also take a look at Josh Berkus' recent testing on this setting:

http://www.powerpostgresql.com/

--
Thomas F. O'Connell
Co-Founder, Information Architect
Sitening, LLC

Strategic Open Source: Open Your i™

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