On Wed, Sep 11, 2013 at 6:11 PM, ascot.m...@gmail.com <ascot.m...@gmail.com>wrote:
> Hi, > > I am using pg 9.2.4 and ubuntu 12.04 to set up a pair of pg-Master and > pg-Slave with streaming replication. > > The archive_command is enabled and the "rsync" is used in pg-Master to > save all its archived WAL files to the 3rd machine for backup purpose, by > default, both fsync and wal_sync_method are commented out in > postgresql.conf: > > archive_command = '(cp %p /usr/pg_arcxlog/%f && rsync -aq %p pg@pg_slave > :/usr/pg_arcxlog/%f' > #fsync = on # turns forced > synchronization on or off > #wal_sync_method = fsync # the default is the first option > > Thus I think the latest WAL might not be flushed to disk from time to time > in pg-Master, therefore the WAL saved in the 3rd server might not contain > the latest WAL. In order to avoid possible data lost, should 'fsync" be > turned ON in pg-Master and pg-Slave? if yes what would be the best > settings of "wal_sync_method" for these two servers respectively? > > Please advise. > regards > I think you are confusing fsync and switching WAL segments for archiving purposes. Here's a link to the docs to get you started: http://www.postgresql.org/docs/9.2/static/runtime-config-wal.html#GUC-ARCHIVE-TIMEOUT fsync is enabled unless you disable it, the fact that it is commented out means that it is set to its default ("on"). wal_sync_method at its default is probably fine, but if you are interested, look at the pg_test_fsync tool: http://www.postgresql.org/docs/9.2/static/pgtestfsync.html
