pg-test-fsync-output-1.txt

60 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                       957.105 ops/sec    1045 usecs/op
        fdatasync                           950.438 ops/sec    1052 usecs/op
        fsync                               229.963 ops/sec    4349 usecs/op
        fsync_writethrough                              n/a
        open_sync                           226.262 ops/sec    4420 usecs/op

Compare file sync methods using two 8kB writes:
(in wal_sync_method preference order, except fdatasync is Linux's default)
        open_datasync                       123.099 ops/sec    8124 usecs/op
        fdatasync                           243.231 ops/sec    4111 usecs/op
        fsync                               119.746 ops/sec    8351 usecs/op
        fsync_writethrough                              n/a
        open_sync                            61.762 ops/sec   16191 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           126.106 ops/sec    7930 usecs/op
         2 *  8kB open_sync writes           60.643 ops/sec   16490 usecs/op
         4 *  4kB open_sync writes           30.649 ops/sec   32627 usecs/op
         8 *  2kB open_sync writes           14.690 ops/sec   68073 usecs/op
        16 *  1kB open_sync writes            7.578 ops/sec  131966 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                 118.514 ops/sec    8438 usecs/op
        write, close, fsync                 121.082 ops/sec    8259 usecs/op

Non-sync'ed 8kB writes:
        write                            452597.638 ops/sec       2 usecs/op

pg-test-fsync-output-2.txt

60 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                       988.971 ops/sec    1011 usecs/op
        fdatasync                           953.926 ops/sec    1048 usecs/op
        fsync                               489.360 ops/sec    2043 usecs/op
        fsync_writethrough                              n/a
        open_sync                           120.705 ops/sec    8285 usecs/op

Compare file sync methods using two 8kB writes:
(in wal_sync_method preference order, except fdatasync is Linux's default)
        open_datasync                       122.197 ops/sec    8184 usecs/op
        fdatasync                           249.566 ops/sec    4007 usecs/op
        fsync                               118.706 ops/sec    8424 usecs/op
        fsync_writethrough                              n/a
        open_sync                            60.956 ops/sec   16405 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           121.616 ops/sec    8223 usecs/op
         2 *  8kB open_sync writes           63.716 ops/sec   15695 usecs/op
         4 *  4kB open_sync writes           31.596 ops/sec   31650 usecs/op
         8 *  2kB open_sync writes           15.152 ops/sec   66000 usecs/op
        16 *  1kB open_sync writes            7.528 ops/sec  132845 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                 116.779 ops/sec    8563 usecs/op
        write, close, fsync                 122.249 ops/sec    8180 usecs/op

Non-sync'ed 8kB writes:
        write                            452763.455 ops/sec       2 usecs/op