| Type: | string |
| Context: | postmaster |
| Restart: | true |
| Since: | 16 |
Ask the kernel to minimize caching effects for relation data and WAL files using O_DIRECT (most Unix-like systems), F_NOCACHE (macOS) or FILE_FLAG_NO_BUFFERING (Windows).
May be set to an empty string (the default) to disable use of direct I/O, or a comma-separated list of operations that should use direct I/O. The valid options are data for main data files, wal for WAL files, and wal_init for WAL files when being initially allocated.
Some operating systems and file systems do not support direct I/O, so non-default settings may be rejected at startup or cause errors.
Currently this feature reduces performance, and is intended for developer testing only.