Postgres / PostgreSQL Benchmarks with pg_test_fsync on a Samsung 970 Evo Plus 2TB PCIe M.2 2280 SSD (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                      1435.065 ops/sec     697 usecs/op
        fdatasync                          1416.766 ops/sec     706 usecs/op
        fsync                               686.976 ops/sec    1456 usecs/op
        fsync_writethrough                              n/a
        open_sync                           689.974 ops/sec    1449 usecs/op

Compare file sync methods using two 8kB writes:
(in wal_sync_method preference order, except fdatasync is Linux's default)
        open_datasync                       719.174 ops/sec    1390 usecs/op
        fdatasync                          1318.471 ops/sec     758 usecs/op
        fsync                               663.196 ops/sec    1508 usecs/op
        fsync_writethrough                              n/a
        open_sync                           341.424 ops/sec    2929 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           665.534 ops/sec    1503 usecs/op
         2 *  8kB open_sync writes          345.405 ops/sec    2895 usecs/op
         4 *  4kB open_sync writes          179.666 ops/sec    5566 usecs/op
         8 *  2kB open_sync writes           81.946 ops/sec   12203 usecs/op
        16 *  1kB open_sync writes           41.146 ops/sec   24304 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                 472.882 ops/sec    2115 usecs/op
        write, close, fsync                 217.122 ops/sec    4606 usecs/op

Non-sync'ed 8kB writes:
        write                            457751.776 ops/sec       2 usecs/op