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-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.


The environment variable PG_COLOR specifies whether to use color in diagnostic messages. Possible values are always, auto and never.

See Also