On Tue, 2003-07-01 at 01:25, Tom Lane wrote:Not without evidence that it doesn't cause performance penalties. ISTM we have been through this discussion recently, and concluded that 32 was the place to set it.
Yes, I was digging through that discussion. The test used shows a 4% difference between 32 and 64.
do 100 times select 2+2+2+2+2+2+ ... iterated 9901 times
There was also this, on disk usage - about 25% penalty going from 32 to 64 (at least for small databases).
Joe Conway wrote: > Tom Lane wrote: >> Did you happen to make any notes about the disk space occupied by the >> database? One thing I was worried about was the bloat that'd occur >> in pg_proc, pg_index, and pg_proc_proname_args_nsp_index. Aside from >> costing disk space, this would indirectly slow things down due to >> more I/O to read these tables --- an effect that probably your test >> couldn't measure, since it wasn't touching very many entries in any >> of those tables. > > > #define INDEX_MAX_KEYS 16 > #define FUNC_MAX_ARGS INDEX_MAX_KEYS > du -h --max-depth=1 /opt/data/pgsql/data/base/ > 2.7M /opt/data/pgsql/data/base/1 > 2.7M /opt/data/pgsql/data/base/16862 > 2.7M /opt/data/pgsql/data/base/16863 > 2.7M /opt/data/pgsql/data/base/16864 > 3.2M /opt/data/pgsql/data/base/16865 > 2.7M /opt/data/pgsql/data/base/16866 > 17M /opt/data/pgsql/data/base > > #define INDEX_MAX_KEYS 32 > #define FUNC_MAX_ARGS INDEX_MAX_KEYS > du -h --max-depth=1 /opt/data/pgsql/data/base/ > 3.1M /opt/data/pgsql/data/base/1 > 3.1M /opt/data/pgsql/data/base/16862 > 3.1M /opt/data/pgsql/data/base/16863 > 3.1M /opt/data/pgsql/data/base/16864 > 3.6M /opt/data/pgsql/data/base/16865 > 3.1M /opt/data/pgsql/data/base/16866 > 19M /opt/data/pgsql/data/base > > #define INDEX_MAX_KEYS 64 > #define FUNC_MAX_ARGS INDEX_MAX_KEYS > du -h --max-depth=1 /opt/data/pgsql/data/base/ > 3.9M /opt/data/pgsql/data/base/1 > 3.9M /opt/data/pgsql/data/base/16862 > 3.9M /opt/data/pgsql/data/base/16863 > 3.9M /opt/data/pgsql/data/base/16864 > 4.4M /opt/data/pgsql/data/base/16865 > 3.9M /opt/data/pgsql/data/base/16866 > 24M /opt/data/pgsql/data/base > > #define INDEX_MAX_KEYS 128 > #define FUNC_MAX_ARGS INDEX_MAX_KEYS > du -h --max-depth=1 /opt/data/pgsql/data/base/ > 5.7M /opt/data/pgsql/data/base/1 > 5.7M /opt/data/pgsql/data/base/16862 > 5.7M /opt/data/pgsql/data/base/16863 > 5.7M /opt/data/pgsql/data/base/16864 > 6.3M /opt/data/pgsql/data/base/16865 > 5.7M /opt/data/pgsql/data/base/16866 > 35M /opt/data/pgsql/data/base >
Here's the thread: http://archives.postgresql.org/pgsql-hackers/2002-08/msg00258.php
Joe
Joe
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