data_corrupted missing chunk number N for toast value N in pg_toast_N — XX001

Symptoms

PostgreSQL could not find an expected chunk of an out-of-line TOAST value. The data is corrupt or incomplete, so it raises SQLSTATE XX001 (data_corrupted).

• A TOAST chunk row is missing.
• The wide value cannot be fully reassembled.
• Classic sign of TOAST-index or heap corruption.

What the server log shows

ERROR:  missing chunk number 0 for toast value 24601 in pg_toast_16390

Why PostgreSQL raises this — what the manual says

Section 66.2.1 Out-of-Line, On-Disk TOAST Storage:

“Each chunk is stored as a separate row in the TOAST table belonging to the owning table.”

Reassembling a TOASTed value requires every chunk. A missing chunk (lost row or a corrupt TOAST index that can’t find it) makes reconstruction impossible, so PostgreSQL reports XX001.

Common causes

• Corruption or loss of rows in the TOAST table.
• A damaged TOAST index that cannot locate chunks.
• Hardware faults or crashes with fsync disabled.

How to fix it

1. REINDEX the TOAST index first — a bad index can cause this even when data is intact.
2. If chunks are truly lost, restore from backup.
3. Run hardware/filesystem checks and consider repairing the affected row after a backup.

Related & next steps

• SQLSTATE XX001 — Data Corrupted (full reference)
• Message: unexpected chunk number for toast value
• Glossary: TOAST

Reference: PostgreSQL 18 Section 73.2 “TOAST”.