Postgres / PostgreSQL Benchmarks with pg_test_fsync on a WDC WD2002FYPS-0 2TB SATA HDD (AMD Ryzen 3600X on X570 Chipset)

pg_test_fsync

$ uname -a
Linux owl 5.4.8-arch1-1 #1 SMP PREEMPT Sat, 04 Jan 2020 23:46:18 +0000 x86_64 GNU/Linux
$ cat /etc/issue 
Arch Linux \r (\l)
$ pg_config --version
PostgreSQL 12.1
$ cd ~

$ 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                        81.276 ops/sec   12304 usecs/op
        fdatasync                            81.940 ops/sec   12204 usecs/op
        fsync                                20.966 ops/sec   47696 usecs/op
        fsync_writethrough                              n/a
        open_sync                            20.980 ops/sec   47665 usecs/op

Compare file sync methods using two 8kB writes:
(in wal_sync_method preference order, except fdatasync is Linux's default)
        open_datasync                        38.486 ops/sec   25983 usecs/op
        fdatasync                            78.133 ops/sec   12799 usecs/op
        fsync                                20.033 ops/sec   49918 usecs/op
        fsync_writethrough                              n/a
        open_sync                            10.324 ops/sec   96862 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            20.785 ops/sec   48111 usecs/op
         2 *  8kB open_sync writes            9.708 ops/sec  103004 usecs/op
         4 *  4kB open_sync writes            5.138 ops/sec  194625 usecs/op
         8 *  2kB open_sync writes            2.411 ops/sec  414803 usecs/op
        16 *  1kB open_sync writes            1.293 ops/sec  773675 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                  20.098 ops/sec   49756 usecs/op
        write, close, fsync                  19.812 ops/sec   50475 usecs/op

Non-sync'ed 8kB writes:
        write                            593734.369 ops/sec       2 usecs/op