On Thu, 2008-11-27 at 21:04 +0900, Koichi Suzuki wrote: > We ran the > benchmark for on hour with chekpoint timeout 30min and completion_target 0.5. > Then, collected all the archive log and run PITR.
> ----------------------+------------+--------------------+--------------- > WAL conditions | Recovery | Amount of | recovery > | time (sec) | physical read (MB) | rate (TX/min) > ----------------------+------------+--------------------+--------------- > w/o prefetch | | | > archived with cp | 6,611 | 5,435 | 402 > FPW=off | | | > ----------------------+------------+--------------------+--------------- > With prefetch | | | > archived with cp | 1,161 | 5,543 | 2,290 > FPW=off | | | > ----------------------+------------+--------------------+--------------- There's clearly a huge gain using prefetch, when we have full_page_writes = off. But that does make me think: Why do we need prefetch at all if we use full page writes? There's nothing to prefetch if we can keep it in cache. I notice we set the checkpoint_timeout to 30 mins, which is long enough to exceed the cache on the standby. I wonder if we reduced the timeout would we use the cache better on the standby and not need readahead at all? Do you have any results to examine cache overflow/shorter timeouts? > w/o prefetch | | | > archived with cp | 1,683 | 801 | 1,458 > FPW=on | | | (8.3) > ----------------------+------------+--------------------+--------------- > w/o prefetch | | | > archived with lesslog | 6,644 | 5,090 | 369 > FPW=on | | | > ----------------------+------------+--------------------+--------------- > With prefetch | | | > archived with cp | 1,415 | 2,157 | 1,733 > FPW=on | | | > ----------------------+------------+--------------------+--------------- > With prefetch | | | > archived with lesslog | 1,196 | 5,369 | 2,051 > FPW=on | | | (This proposal) > ----------------------+------------+--------------------+--------------- So I'm wondering if we only need prefetch because we're using lesslog? If we integrated lesslog better into the new replication would we be able to forget about doing the prefetch altogether? -- Simon Riggs www.2ndQuadrant.com PostgreSQL Training, Services and Support -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
