Greg Smith <greg@xxxxxxxxxxxxxxx> wrote: > What I do to quantify that is...well, the attached shows it better > than I can describe; only works on 9.0 or later as it depends on a > feature I added for this purpose there. It measures exactly how > much buffer cache churn happened during a test, in this case > creating a pgbench database. I'm not entirely sure I understand what I'm supposed to get from that. On a 3GB workstation, a compile from a recent HEAD checkout, with a default postgresql.conf file, I get this: -[ RECORD 1 ]------+------------------------------ now | 2010-08-04 14:25:46.683766-05 checkpoints_timed | 0 checkpoints_req | 0 buffers_checkpoint | 0 buffers_clean | 0 maxwritten_clean | 0 buffers_backend | 0 buffers_alloc | 73 Initializing pgbench -[ RECORD 1 ]------+------------------------------ now | 2010-08-04 14:27:49.062551-05 checkpoints_timed | 0 checkpoints_req | 0 buffers_checkpoint | 0 buffers_clean | 0 maxwritten_clean | 0 buffers_backend | 633866 buffers_alloc | 832 I boost shared_buffers from 32MB to 320MB, restart, and get this: -[ RECORD 1 ]------+------------------------------ now | 2010-08-04 14:30:42.816719-05 checkpoints_timed | 0 checkpoints_req | 0 buffers_checkpoint | 0 buffers_clean | 0 maxwritten_clean | 0 buffers_backend | 0 buffers_alloc | 0 Initializing pgbench -[ RECORD 1 ]------+------------------------------ now | 2010-08-04 14:32:40.750098-05 checkpoints_timed | 0 checkpoints_req | 0 buffers_checkpoint | 0 buffers_clean | 0 maxwritten_clean | 0 buffers_backend | 630794 buffers_alloc | 2523 So run time dropped from 123 seconds to 118 seconds, buffers_backend dropped by less than 0.5%, and buffers_alloc went up. Assuming this is real, and not just "in the noise" -- what conclusions would you draw from this? Dedicating an additional 10% of my free memory got me a 4% speed improvement? Was I supposed to try with other scales? Which ones? -Kevin -- Sent via pgsql-performance mailing list (pgsql-performance@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
