serialization_failure could not serialize access due to read/write dependencies — 40001

Symptoms

A SERIALIZABLE transaction was aborted because of read/write dependencies with other concurrent transactions that could violate serializability. PostgreSQL raises SQLSTATE 40001 (serialization_failure).

• Serializable Snapshot Isolation detected an unsafe dependency cycle.
• Common under SERIALIZABLE isolation with concurrency.
• The transaction should be retried.

What the server log shows

ERROR:  could not serialize access due to read/write dependencies among transactions
DETAIL:  Reason code: Canceled on identification as a pivot.
HINT:  The transaction might succeed if retried.

Why PostgreSQL raises this — what the manual says

Section 13.2.3 Serializable Isolation Level:

“Applications using this level must be prepared to retry transactions due to serialization failures.”

Serializable Snapshot Isolation tracks read/write dependencies between concurrent transactions. When it finds a pattern (a “pivot”) that could yield a result inconsistent with some serial order, it aborts a transaction with 40001 to preserve serializability.

Common causes

• Concurrent SERIALIZABLE transactions with conflicting read/write sets.
• Hotspots where many transactions read and write overlapping data.
• Higher concurrency increasing dependency cycles.

How to fix it

1. Retry the transaction — this error is expected and retryable.
2. Keep SERIALIZABLE transactions short to reduce conflicts.
3. Use explicit locking or a lower isolation level if appropriate for the workload.

Related & next steps

• SQLSTATE 40001 — Serialization Failure (full reference)
• Message: deadlock detected
• Glossary: Serializable isolation

Reference: PostgreSQL 18 Section 13.2 “Transaction Isolation”.