Re: [PATCH] Revert default wal_sync_method to fdatasync on Linux 2.6.33+

Greg, All:

Results for Solaris 10u8, on ZFS on a 7-drive attached storage array:

bash-3.00# ./test_fsync -f /dbdata/pgdata/test.out
Loops = 10000

Simple write:
        8k write                      59988.002/second

Compare file sync methods using one write:
        open_datasync 8k write          214.125/second
        (unavailable: o_direct)
        open_sync 8k write              222.155/second
        (unavailable: o_direct)
        8k write, fdatasync             214.086/second
        8k write, fsync                 215.035/second
        (unavailable: fsync_writethrough)

Compare file sync methods using two writes:
        2 open_datasync 8k writes       108.227/second
        (unavailable: o_direct)
        2 open_sync 8k writes           106.935/second
        (unavailable: o_direct)
        8k write, 8k write, fdatasync   205.525/second
        8k write, 8k write, fsync       210.483/second
        (unavailable: fsync_writethrough)

Compare open_sync with different sizes:
        open_sync 16k write             211.481/second
        2 open_sync 8k writes           106.202/second

Test if fsync on non-write file descriptor is honored:
(If the times are similar, fsync() can sync data written
on a different descriptor.)
        8k write, fsync, close          207.499/second
        8k write, close, fsync          213.656/second




-- 
                                  -- Josh Berkus
                                     PostgreSQL Experts Inc.
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