Greg Smith wrote:
On Sat, 21 Apr 2007, Nelson Kotowski wrote:
I identified that the cluster command over the lineitem table (cluster
idx_lineitem on lineitem) is the responsible. I got to this conclusion
because when i run it in the 1GB and 2GB database i am able to
complete this script in 10 and 30 minutes each. But when i run this
command over the 5GB database, it simply seems as it won't end.
Have you looked in the database log files for messages? Unless you
changed some other parameters from the defaults that you didn't mention,
I'd expect you've got a constant series of "checkpoint occuring too
frequently" errors in there, which would be a huge slowdown on your
index rebuild. Slowdowns from checkpoints would get worse with an
increase of shared_buffers, as you report.
Index builds don't write WAL, unless archive_command has been set. A
higher shared_buffers setting can hurt index build performance, but for
a different reason: the memory spent on shared_buffers can't be used for
sorting and caching the sort tapes.
The default setting for checkpoint_segments of 3 is extremely low for
even a 1GB database. Try increasing that to 30, restart the server, and
rebuild the index to see how much the 1GB case speeds up. If it's
significantly faster (it should be), try the 5GB one again.
A good advice, but it's unlikely to make a difference at load time.
BTW: With CVS HEAD, if you create the table in the same transaction (or
TRUNCATE) as you load the data, the COPY will skip writing WAL which can
give a nice speedup.
--
Heikki Linnakangas
EnterpriseDB http://www.enterprisedb.com
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