PostgreSQL Error 40001: Serialization Failure

PostgreSQL SQLSTATE 40001 is serialization_failure. It means PostgreSQL canceled a transaction to prevent concurrent transactions from producing a result that cannot be explained by a valid serial order. The exact message depends on the conflict, but the SQLSTATE remains 40001. See the PostgreSQL error-code appendix.

This is a concurrency-control error, not a syntax error or a sign that the server is unavailable. It can occur at REPEATABLE READ or SERIALIZABLE isolation when concurrent work conflicts with the transaction’s snapshot or read/write dependencies. PostgreSQL requires applications using these isolation levels to be prepared to retry failed transactions; see Transaction Isolation.

Check the isolation level and the first error

Capture the SQLSTATE, complete error message, and the transaction or request ID from the application logs. If you can still query through the affected connection, inspect its current isolation level:

SHOW transaction_isolation;

The default is read committed, but a database, role, session, connection startup option, or explicit SET TRANSACTION can change it. Look for a repeatable-read or serializable transaction in the code path that failed. A serialization error can be raised by a statement or when the transaction is being committed, so log the complete transaction outcome rather than assuming the last statement alone is responsible.

If the client reports 25P02 after 40001, the transaction is already aborted and later statements are follow-on errors. Find the first 40001 and roll back the transaction; see PostgreSQL Error 25P02: current transaction is aborted.

Roll back and retry the whole transaction

After 40001, abort the failed transaction and start a new one. Retry the complete unit of work from its first read, so PostgreSQL can take a fresh snapshot and the application can recalculate decisions using current data. Retrying only the statement that raised the error can reuse stale reads and produce an incorrect result. PostgreSQL’s guidance for serialization failures is to retry the whole transaction.

In application code, use a bounded retry policy and an appropriate delay between attempts. Make sure the retried work is safe to repeat: keep external effects such as sending email or charging a payment outside the retried transaction, or protect them with an idempotency mechanism. In a serializable transaction, do not treat data read by the transaction as final until the transaction commits successfully.

Do not lower the isolation level just to silence the error. First confirm the consistency guarantee the application needs; changing from REPEATABLE READ or SERIALIZABLE to READ COMMITTED can change what concurrent work the application is allowed to observe.

Distinguish serialization failures from deadlocks

• 40001 — serialization_failure: PostgreSQL rejected a transaction because of an isolation or serialization conflict. Retry the complete transaction from fresh reads.
• 40P01 — deadlock_detected: PostgreSQL found a lock cycle and aborted one transaction. Consistent lock ordering can reduce these conflicts; see PostgreSQL Error 40P01: deadlock detected.
• 25P02 — in_failed_sql_transaction: a previous statement failed inside the open transaction, so later statements are rejected until rollback or savepoint recovery.

For other PostgreSQL SQLSTATE guides, browse PostgreSQL Error Troubleshooting.