Re: We really ought to do something about O_DIRECT and data=journalled on ext4

All,

Geirth's results from his FreeBSD 7.1 server using 8.4's test_fsync:

Simple write timing:       write                    0.007081

Compare fsync times on write() and non-write() descriptor:
If the times are similar, fsync() can sync data written
on a different descriptor.       write, fsync, close      5.937933       write, close, fsync      8.056394

Compare one o_sync write to two:       one 16k o_sync write     7.366927       two 8k o_sync writes    15.299300

Compare file sync methods with one 8k write:       (o_dsync unavailable)       open o_sync, write       7.512682
(fdatasyncunavailable)       write, fsync             5.856480
 

Compare file sync methods with two 8k writes:       (o_dsync unavailable)       open o_sync, write      15.472910
(fdatasyncunavailable)       write, fsync             5.880319
 


... again, open_sync does not look very impressive.

--                                  -- Josh Berkus                                    PostgreSQL Experts Inc.
                        http://www.pgexperts.com