Postgres Filesystem Benchmark of an Intel Optane 900P 480GB PCIe SSD mounted in a PCIe 4.0 x8 slot (linked directly to CPU, not to chipset)

pg_test_fsync

$ uname -a
Linux owl 5.5.8-arch1-1 #1 SMP PREEMPT Fri, 06 Mar 2020 00:57:33 +0000 x86_64 GNU/Linux
$ cat /etc/os-release 
NAME="Arch Linux"
PRETTY_NAME="Arch Linux"
ID=arch
BUILD_ID=rolling
ANSI_COLOR="0;36"
HOME_URL="https://www.archlinux.org/"
DOCUMENTATION_URL="https://wiki.archlinux.org/"
SUPPORT_URL="https://bbs.archlinux.org/"
BUG_REPORT_URL="https://bugs.archlinux.org/"
$ pg_config --version
PostgreSQL 12.2

$ pg_test_fsync
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                     34040.623 ops/sec      29 usecs/op
        fdatasync                         33762.892 ops/sec      30 usecs/op
        fsync                             31874.647 ops/sec      31 usecs/op
        fsync_writethrough                              n/a
        open_sync                         31882.292 ops/sec      31 usecs/op

Compare file sync methods using two 8kB writes:
(in wal_sync_method preference order, except fdatasync is Linux's default)
        open_datasync                     28638.931 ops/sec      35 usecs/op
        fdatasync                         28652.748 ops/sec      35 usecs/op
        fsync                             28329.926 ops/sec      35 usecs/op
        fsync_writethrough                              n/a
        open_sync                         28294.717 ops/sec      35 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         28022.049 ops/sec      36 usecs/op
         2 *  8kB open_sync writes        28228.306 ops/sec      35 usecs/op
         4 *  4kB open_sync writes        16144.664 ops/sec      62 usecs/op
         8 *  2kB open_sync writes         4352.070 ops/sec     230 usecs/op
        16 *  1kB open_sync writes         1836.779 ops/sec     544 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               31803.079 ops/sec      31 usecs/op
        write, close, fsync               31768.603 ops/sec      31 usecs/op

Non-sync'ed 8kB writes:
        write                            569657.775 ops/sec       2 usecs/op