gistfile1.txt

$ bin/pg_test_fsync -f /data/m/my/data/mysql.ibd
5 seconds per test
O_DIRECT supported on this platform for open_datasync and open_sync.

Compare file sync methods using one 8kB write:
(in wal_sync_method preference order, except fdatasync is Linux's default)
        open_datasync                       435.834 ops/sec    2294 usecs/op
        fdatasync                           739.356 ops/sec    1353 usecs/op
        fsync                               275.887 ops/sec    3625 usecs/op
        fsync_writethrough                              n/a
        open_sync                           289.213 ops/sec    3458 usecs/op

Compare file sync methods using two 8kB writes:
(in wal_sync_method preference order, except fdatasync is Linux's default)
        open_datasync                       215.263 ops/sec    4645 usecs/op
        fdatasync                           664.017 ops/sec    1506 usecs/op
        fsync                               298.834 ops/sec    3346 usecs/op
        fsync_writethrough                              n/a
        open_sync                           168.928 ops/sec    5920 usecs/op

Compare open_sync with different write sizes:
(This is designed to compare the cost of writing 16kB in different write
open_sync sizes.)
         1 * 16kB open_sync write           297.779 ops/sec    3358 usecs/op
         2 *  8kB open_sync writes          159.258 ops/sec    6279 usecs/op
         4 *  4kB open_sync writes           79.624 ops/sec   12559 usecs/op
         8 *  2kB open_sync writes           37.313 ops/sec   26801 usecs/op
        16 *  1kB open_sync writes           18.225 ops/sec   54871 usecs/op

Test if fsync on non-write file descriptor is honored:
(If the times are similar, fsync() can sync data written on a different
descriptor.)
        write, fsync, close                 291.049 ops/sec    3436 usecs/op
        write, close, fsync                 302.126 ops/sec    3310 usecs/op

Non-sync'ed 8kB writes:
        write                            253601.768 ops/sec       4 usecs/op