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.
                        http://www.pgexperts.com