On Fri, Aug 26, 2011 at 10:46:33AM +0200, Tomas Vondra wrote: > Hmmm, let me explain what led me to this patch - right now I'm doing a > comparison of filesystems with various block sizes (both fs and db > blocks). I've realized that the db block size significantly influences > frequency of checkpoints and amount of data to write, so I'm collecting > data from pg_stat_bgwriter too. The benchmark goes like this > > 1. collect pg_stat_bgwriter stats > 2. run pgbench for 10 minutes > 3. collect pg_stat_bgwriter stats (to compute difference with (1)) > 4. kill the postmaster > > The problem is that when checkpoint stats are collected, there might be a > checkpoint in progress and in that case the stats are incomplete. In some > cases (especially with very small db blocks) this has significant impact > because the checkpoints are less frequent.
Could you remove this hazard by adding a step "2a. psql -c CHECKPOINT"? -- Noah Misch http://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Training & Services -- Sent via pgsql-hackers mailing list (firstname.lastname@example.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers