The error is raised when a branch (subordinate) transaction in a two-phase commit tries to set an isolation level that the coordinator forbids, typically SERIALIZABLE.
PostgreSQL Error 25004 inappropriate_isolation_level_for_branch_transaction appears when a branch transaction sets an isolation level, such as SERIALIZABLE, that is not permitted during two-phase commit processing. Use the isolation level mandated by the coordinator or omit SET TRANSACTION altogether to resolve the issue.
PostgreSQL Error 25004
Error 25004 signals that a subordinate (branch) transaction in a distributed or prepared transaction attempted to use an isolation level that is considered unsafe or incompatible with two-phase commit rules.
PostgreSQL raises this condition before the transaction is prepared, preventing inconsistent visibility rules from entering the global transaction log.
Fixing it quickly avoids data anomalies in coordinated systems.
The condition surfaces during BEGIN, SET TRANSACTION, or START TRANSACTION commands that specify SERIALIZABLE or REPEATABLE READ while the backend is already acting as a branch of a prepared transaction.
It can also appear inside foreign data-wrapper transactions where an external coordinator governs isolation policies.
Leaving the problem unresolved blocks the transaction, leading to stuck prepared states or forced rollbacks.
Applications relying on two-phase commit will fail their unit of work, causing downstream errors and potential data loss.
Prompt remediation restores transaction flow, keeps replicas consistent, and maintains ACID guarantees.
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Issuing BEGIN ISOLATION LEVEL SERIALIZABLE while enlisted in a two-phase commit branch triggers the error because the coordinator cannot enforce global serializability.
Attempting to change isolation after the transaction has been marked as prepared violates the transaction state machine, producing code 25004.
Some ORMs and JDBC drivers automatically set SERIALIZABLE for audit tables.
If the connection is part of XA or foreign transactions, PostgreSQL rejects the change.
External transaction managers may dictate READ COMMITTED while the application code forces REPEATABLE READ, causing isolation conflicts.
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Generally no. Most coordinators disallow SERIALIZABLE for branch transactions because global serializability cannot be guaranteed across systems.
It rarely shows up unless you explicitly call PREPARE TRANSACTION. Standard single-node transactions are not affected.
Yes. Setting it to READ COMMITTED or REPEATABLE READ at the database level avoids accidental SERIALIZABLE requests from drivers.
Galaxy’s SQL editor flags SERIALIZABLE inside prepared blocks and offers AI suggestions to drop or adjust the isolation level before you run the query, preventing runtime failures.
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