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

Symptoms

Under SERIALIZABLE isolation, PostgreSQL detected a dangerous read/write dependency cycle and aborted a transaction to preserve serializable correctness. It raises SQLSTATE 40001 (serialization_failure).

• Only occurs under SERIALIZABLE isolation (SSI).
• The transaction can usually succeed if simply retried.
• A HINT recommends retrying the transaction.

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, during write.
HINT:  The transaction might succeed if retried.

Why PostgreSQL raises this — what the manual says

Section 13.2.3 Serializable Isolation Level:

“They are used to identify and flag dependencies among concurrent Serializable transactions which in certain combinations can lead to serialization anomalies.”

Serializable Snapshot Isolation tracks read/write dependencies between concurrent transactions. When it finds a cycle that could violate serializability, it cancels one transaction (the pivot) with 40001 so the committed outcome is still equivalent to some serial order.

Common causes

• Concurrent SERIALIZABLE transactions with interleaving reads and writes.
• High contention on overlapping data sets.
• Long-running serializable transactions increasing conflict windows.

How to fix it

1. Retry the transaction on 40001 — this is expected under SERIALIZABLE.
2. Keep serializable transactions short and touch fewer rows.
3. Consider REPEATABLE READ if SSI guarantees are stronger than you need.

Related & next steps

• SQLSTATE 40001 — Serialization Failure (full reference)
• Message: could not serialize access due to concurrent update
• Glossary: Serializable

Reference: PostgreSQL 18 Section 13.2 “Transaction Isolation”.