could not open critical system index n

Symptoms

A statement failed with SQLSTATE XX001 (data_corrupted), reported at severity PANIC. This is a Internal Error condition: PostgreSQL emits the message could not open critical system index n.

• The client receives SQLSTATE XX001 (data corrupted).
• The operation is rejected at PANIC level; the statement does not complete.

What the server log shows

PANIC:  could not open critical system index n

Why PostgreSQL raises this

Class XX (Internal Error) indicates a condition that should not normally occur — often a sign of data corruption or a server bug. These warrant careful investigation.

As described in PostgreSQL’s Chapter 30 Reliability and the Write-Ahead Log and Appendix A (PostgreSQL Error Codes), SQLSTATE XX001 carries the condition name data_corrupted in class Internal Error. (Paraphrased — see the linked reference for the exact wording.)

Common causes

• Data or index corruption (often storage/hardware related).
• An unexpected internal state or a server bug.
• A failed consistency check during execution.

How to fix it

1. Capture the full message, context, and server version.
2. Check storage/hardware and recent crash history.
3. Take a backup and consider reporting a reproducible case upstream.

Version applicability

This message is present in PostgreSQL 15, 16, 17, 18 and 19.

Related & next steps

• SQLSTATE XX001 — Data Corrupted (full reference)
• PostgreSQL error code index

Reference: PostgreSQL Chapter 30 Reliability and the Write-Ahead Log.