# pg_test_fsync ## Name pg_test_fsync -- determine fastest wal_sync_method for PostgreSQL ## Synopsis `pg_test_fsync` [`_option_`...] ## Description pg_test_fsync is intended to give you a reasonable idea of what the fastest [wal_sync_method](#calibre_link-1432) 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 transaction 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](#calibre_link-1621). ## Options 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_xlog` directory is or will be placed in. (`pg_xlog` contains the WAL files.) The default is `pg_test_fsync.out` in the current directory. `-s` `--secs-per-test` 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` `--version` Print the pg_test_fsync version and exit. `-?` `--help` Show help about pg_test_fsync command line arguments, and exit. ## Author Bruce Momjian `<[bruce@momjian.us](mailto:bruce@momjian.us)>` ## See Also [postgres](#calibre_link-1033)