PostgreSQL on OS X uses a special fsync method by default named 'fsync_writethrough'. If you do this on your database you should be able to confirm it's using it:
·open_datasync (write WAL files with open() option O_DSYNC)
·fdatasync (call fdatasync() at each commit)
·fsync_writethrough (call fsync() at each commit, forcing write-through of any disk write cache)
·fsync (call fsync() at each commit)
·open_sync (write WAL files with open() option O_SYNC)
Not all of these choices are available on all platforms. The default is the first method in the above list that is supported by the platform.So apparently, my system supports open_datasync, and since it is the first method, that is the default.
