pg_test_fsync — determine fastest wal_sync_method for PostgreSQL
pg_test_fsync [option...]
  pg_test_fsync is intended to give you a reasonable
  idea of what the fastest wal_sync_method is on your
  specific system,
  as well as supplying diagnostic information in the event of an identified I/O
  problem.  However, differences shown by
  pg_test_fsync might not make any significant
  difference in real database throughput, especially since many database servers
  are not speed-limited by their write-ahead logs.
  pg_test_fsync reports average file sync operation
  time in microseconds for each wal_sync_method, which can also be used to
  inform efforts to optimize the value of commit_delay.
 
pg_test_fsync accepts the following command-line options:
-f--filename        Specifies the file name to write test data in.
        This file should be in the same file system that the
        pg_wal directory is or will be placed in.
        (pg_wal contains the WAL files.)
        The default is pg_test_fsync.out in the current
        directory.
       
-s--secs-per-testSpecifies the number of seconds for each test. The more time per test, the greater the test's accuracy, but the longer it takes to run. The default is 5 seconds, which allows the program to complete in under 2 minutes.
-V--versionPrint the pg_test_fsync version and exit.
-?--helpShow help about pg_test_fsync command line arguments, and exit.