I have run fsync_test on this partition, and I got 2500+ for all kind of sync method.
dmesg says: blkfront: xvde: barriers enabled blkfront: xvda: barriers enabled One thing I haven't mentioned yet, that this a VM virtualized with Xen. Perhaps this has some effect. Thanks, Otto 2011/12/20 Greg Smith <g...@2ndquadrant.com> > On 12/19/2011 10:52 AM, Havasvölgyi Ottó wrote: > >> PgSql 9.1.2 >> Debian, 2.6.32 kernel >> WAL filesystem: ext4 with defaults >> > > There's a pg_test_fsync program included with the postgresql-contrib > package that might help you sort out what's going on here. This will > eliminate the possibility that you're doing something wrong with pgbench, > and give an easy to interpret number relative to the drive RPM rate. > > You said default settings, which eliminated "nobarrier" as a cause here. > The only other thing I know of that can screw up fsync here is using one > of the incompatible LVM features to build your filesystem. I don't know > which currently work and don't work, but last I checked there were a few > ways you could set LVM up that would eliminate filesystem barriers from > working properly. You might check: > > dmesg | grep barrier > > To see if you have any kernel messages related to this. > > Here's a pg_test_fsync example from a Debian system on 2.6.32 with ext4 > filesystem and 7200 RPM drive, default mount parameters and no LVM: > > $ ./pg_test_fsync > 2000 operations per test > O_DIRECT supported on this platform for open_datasync and open_sync. > > Compare file sync methods using one 8kB write: > (in wal_sync_method preference order, except fdatasync > is Linux's default) > open_datasync n/a > fdatasync 113.901 ops/sec > fsync 28.794 ops/sec > fsync_writethrough n/a > open_sync 111.726 ops/sec > > Compare file sync methods using two 8kB writes: > (in wal_sync_method preference order, except fdatasync > is Linux's default) > open_datasync n/a > fdatasync 112.637 ops/sec > fsync 28.641 ops/sec > fsync_writethrough n/a > open_sync 55.546 ops/sec > > Compare open_sync with different write sizes: > (This is designed to compare the cost of writing 16kB > in different write open_sync sizes.) > 16kB open_sync write 111.909 ops/sec > 8kB open_sync writes 55.278 ops/sec > 4kB open_sync writes 28.026 ops/sec > 2kB open_sync writes 14.002 ops/sec > 1kB open_sync writes 7.011 ops/sec > > Test if fsync on non-write file descriptor is honored: > (If the times are similar, fsync() can sync data written > on a different descriptor.) > write, fsync, close 28.836 ops/sec > write, close, fsync 28.890 ops/sec > > Non-Sync'ed 8kB writes: > write 112113.908 ops/sec > > -- > Greg Smith 2ndQuadrant US g...@2ndquadrant.com Baltimore, MD > PostgreSQL Training, Services, and 24x7 Support www.2ndQuadrant.us > > > -- > Sent via pgsql-general mailing list (pgsql-general@postgresql.org) > To make changes to your subscription: > http://www.postgresql.org/**mailpref/pgsql-general<http://www.postgresql.org/mailpref/pgsql-general> >
