---
title: "pg_test_fsync"
id: pgtestfsync
pg_version: "20devel"
---

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# pg_test_fsync — determine fastest `wal_sync_method` for PostgreSQL

## Synopsis

```
pg_test_fsync [option...] 
```

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## Description

pg_test_fsync is intended to give you a reasonable idea of what the fastest [`wal_sync_method` (`enum`)](runtime-config-wal.md#guc-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` (`integer`)](runtime-config-wal.md#guc-commit-delay). 

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## 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_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.  

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## Environment

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

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## See Also

[postgres](app-postgres.md)