data_directory_mode

Definition PG 18 manual

On Unix systems this parameter reports the permissions the data directory (defined by data_directory) had at server startup. (On Microsoft Windows this parameter will always display 0700.) See the initdb -g option for more information.

How it works

Shows the mode of the data directory. It is read-only and cannot be changed with SET or configuration-file edits.

It reports the effective Unix permission mode of the data directory, commonly 0700 or group-readable 0750, in decimal pg_settings representation.

Interpret it with block_size, data_checksums, debug_assertions. Applications and operations tooling may read data_directory_mode for capability or environment detection, but cannot SET it; cross-cluster comparisons must account for build, initdb, and current-database differences.

Operational considerations

Trying to change read-only data_directory_mode with SET or a configuration file.

Assuming every cluster, database, or vendor build reports the same value.

Ignoring the value in file-format or feature-compatibility checks.

Treating reported metadata as a performance target instead of an environment fact.

Workload guidance

OLAP: Not tunable. Use data_directory_mode to verify format, build, or resource assumptions on analytical nodes and keep every read/write candidate compatible.

OLTP: Not tunable. Record data_directory_mode as a deployment/capability fact; if it is unexpected, fix the binary, initdb, or database-creation process rather than trying SET.

SMALL: Not tunable. Preserve it in inventory and incident reports; do not custom-build or rebuild merely to change it without a demonstrated compatibility need.