ignore_system_indexes

Definition PG 18 manual

Ignore system indexes when reading system tables (but still update the indexes when modifying the tables). This is useful when recovering from damaged system indexes. This parameter cannot be changed after session start.

How it works

ignore_system_indexes makes a newly started backend read system catalogs without using their indexes, while catalog modifications still update the indexes. It is intended to recover from damaged system indexes.

Because its backend context is fixed at session start, changing the setting inside an existing session is ineffective. Catalog scans can become very slow.

The mode does not repair an index; it only creates a path to inspect data and REINDEX the damaged system index. Leaving it enabled hides symptoms and imposes broad catalog overhead. Its backend context fixes the value during connection startup; an existing session cannot change it.

Operational considerations

Leaving ignore_system_indexes enabled after the bounded diagnostic or recovery task.

Running the experiment on the only copy of production data.

Underestimating log, core-file, temporary-file, WAL, CPU, or connection-slot amplification.

Treating a server that merely starts or completes a query as proof that data and behavior are correct.

Workload guidance

OLAP: Read-only analytics does not make ignore_system_indexes safe: corrupted pages can still poison results or structures. Use only on a disposable salvage copy with explicit acceptance of lost data.

OLTP: Never use ignore_system_indexes as tuning or a steady-state availability setting. Stop writes, preserve immutable copies, exhaust backup/storage repair, document expected data loss, salvage narrowly, rebuild, and validate before any return to service.

SMALL: Do not enable ignore_system_indexes merely because no replica exists. Preserve the original first and seek a clean backup; this switch can convert visible corruption into silent loss.