On Jan 18, 2011, at 5:16 PM, Bruce Momjian wrote: > A.M. wrote: >> >> On Jan 18, 2011, at 3:55 PM, Bruce Momjian wrote: >> >>> I have modified test_fsync to use test labels that match wal_sync_method >>> values, and and added more tests for open_sync with different sizes. >>> This should make the program easier for novices to understand. Here is >>> a test run for Ubuntu 11.04: >>> >>> $ ./test_fsync >>> 2000 operations per test >>> >>> Compare file sync methods using one 8k write: >>> (in wal_sync_method preference order, except fdatasync >>> is Linux's default) >>> open_datasync (non-direct I/O)* 85.127 ops/sec >>> open_datasync (direct I/O) 87.119 ops/sec >>> fdatasync 81.006 ops/sec >>> fsync 82.621 ops/sec >>> fsync_writethrough n/a >>> open_sync (non-direct I/O)* 84.412 ops/sec >>> open_sync (direct I/O) 91.006 ops/sec >>> * This non-direct I/O mode is not used by Postgres. >> >> I am curious how this is targeted at novices. A naive user might enable >> the "fastest" option which could be exactly wrong. For this to be useful >> to novices, I suspect the tool will need to generate platform-specific >> suggestions, no? > > Uh, why isn't the fastest option right for them? It is hardware/kernel > specific when you run it --- how could it be better?
Because the fastest option may not be syncing to disk. For example, the only option that makes sense on OS X is fsync_writethrough- it would be helpful if the tool pointed that out (on OS X only, obviously). Cheers, M -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
