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

    • 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

    • Specifies 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

    • Print the pg_test_fsync version and exit.
  • -?

    • Show help about pg_test_fsync command line arguments, and exit.

See Also