I wanted to see this difference. It is somewhat ad hoc.
However, It is more effective than it doesn't show it at all.

-- MinGW(win32) --
$ test_fsync
Simple write timing:
       write                    3.644000

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     40.543000
       write, close, fsync     47.033000

Compare one o_sync write to two:
(o_sync unavailable) open o_dsync, write 0.094000

       (fdatasync unavailable)
       write, fsync,           26.700000

Compare file sync methods with 2 8k writes:
       open o_dsync, write      0.203000
       (fdatasync unavailable)
       write, fsync,           27.920000

Hiroshi Saito

Attachment: test_fsync_patch
Description: Binary data

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