Many thanks for all your advice and we will use Greg Smith's book on performance to incrementaly tune our environment.
Regards, Lawrence Cohan. -----Original Message----- From: Kevin Grittner [mailto:kevin.gritt...@wicourts.gov] Sent: April-21-11 3:38 PM To: pgsql-bugs@postgresql.org; Lawrence Cohan Subject: RE: [BUGS] Postgres not using indexes Lawrence Cohan <lco...@web.com> wrote: > We managed to put together a new test server running PG 9.0.2 on > 2socketsx6cores = 12CPU with 64 GB RAM against a 3PAR 10TB SAN. We > kept the settings I submitted already (and enclosed below) and > after 12 hours of pounding the box with PGBENCH running 8 scripts > to perform all of INSERT/UPDATE/DELETE/SELECT statements we wanted > we got a pretty good picture of what can do with those settings. > We got a load average of 60 with CPU up and around that 60% mark, > pushing through about 1400 transactions per second for 12 hours. > We made the changes as suggested and listed below but the > throughput dropped from 1400 t/s to 400 t/s and I suspect are the > "stalled" transactions you mentioned about. > > Here's what we changed: > > Current Settings Test Settings > ================================================================ > shared_buffers = 500MB shared_buffers = 8GB > effective_cache_size = 2GB effective_cache_size = 32GB To make sure I understand, are the "Current Settings" the ones which performed better? > Just to be 100% accurate we ask you what do you mean by: > > 1) "Make the background writer more aggressive and/or back > off on shared_memory, so that there isn't such a glut of dirty > pages to Write during a checkpoint." > > By aggressive does he mean changing any of the following? > # - Background Writer - > > #bgwriter_delay = 200ms > #bgwriter_lru_maxpages = 100 > #bgwriter_lru_multiplier = 2.0 We use these overrides: bgwriter_lru_maxpages = 1000 bgwriter_lru_multiplier = 4.0 > Or we should be better of by the checkpoint segment handling - any > of the below: > # - Checkpoints - > > checkpoint_segments = 64 > #checkpoint_timeout = 5min > #checkpoint_completion_target = 0.5 > checkpoint_warning = 60s You might consider increasing checkpoint_timeout if you can tolerate the increased recovery time if there is a crash. You should probably boost checkpoint_completion_target to 0.8 or 0.9. Really, if you don't already have it, you should get a copy of Greg Smith's recent book on performance: http://www.postgresql.org/docs/books/ It gives good descriptions of all of these parameters and advice on incremental tuning to find you best settings. The fact that you listed shared_buffers and effective_cache_size together at least suggests that you don't yet grasp the role of these settings. One affects how much memory PostgreSQL allocates; the other has absolutely nothing to do with that. effective_cache_size affects costs assigned to various plans, thereby affecting plan choice. While a high shared_buffers setting might lead to a glut of writes around commit time, setting effective_cache_size incorrectly might lead to plans which don't read the data efficiently. Seeing what vmstat or iostat say during a slow episode, and seeing whether the episodes correspond to checkpoints, will give you a better indication of where the problem lies. -Kevin Attention: The information contained in this message and or attachments is intended only for the person or entity to which it is addressed and may contain confidential and/or privileged material. Any review, retransmission, dissemination or other use of, or taking of any action in reliance upon, this information by persons or entities other than the intended recipient is prohibited. If you received this in error, please contact the sender and delete the material from any system and destroy any copies. -- Sent via pgsql-bugs mailing list (pgsql-bugs@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-bugs
