# Pastebin 5YJ1EWZE
[postgres@aitosfsdb00 ~]$ /usr/pgsql-11/bin/pg_test_fsync --help
Usage: pg_test_fsync [-f FILENAME] [-s SECS-PER-TEST]
[postgres@aitosfsdb00 ~]$ /usr/pgsql-11/bin/pg_test_fsync -s 10 -f /tmp/sysc.out
10 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                                  n/a*
        fdatasync                        313605.214 ops/sec       3 usecs/op
        fsync                            314363.297 ops/sec       3 usecs/op
        fsync_writethrough                              n/a
        open_sync                                      n/a*
* This file system and its mount options do not support direct
  I/O, e.g. ext4 in journaled mode.

Compare file sync methods using two 8kB writes:
(in wal_sync_method preference order, except fdatasync is Linux's default)
        open_datasync                                  n/a*
        fdatasync                        200460.378 ops/sec       5 usecs/op
        fsync                            198070.597 ops/sec       5 usecs/op
        fsync_writethrough                              n/a
        open_sync                                      n/a*
* This file system and its mount options do not support direct
  I/O, e.g. ext4 in journaled mode.

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                      n/a*
         2 *  8kB open_sync writes                     n/a*
         4 *  4kB open_sync writes                     n/a*
         8 *  2kB open_sync writes                     n/a*
        16 *  1kB open_sync writes                     n/a*

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              103188.535 ops/sec      10 usecs/op
        write, close, fsync              104203.139 ops/sec      10 usecs/op

Non-sync'ed 8kB writes:
        write                            187219.888 ops/sec       5 usecs/op
[postgres@aitosfsdb00 ~]$