This error occurs when attempting to set a different transaction isolation level within a subtransaction (savepoint) or when the isolation level does not match between a parent transaction and its branch.
The error code 25004 (inappropriate_isolation_level_for_branch_transaction) indicates that you attempted to establish a transaction isolation level that is incompatible with the current context. In PostgreSQL, subtransactions (created via SAVEPOINT or PL/pgSQL exception blocks) inherit and must maintain the isolation level of their parent transaction. This error is part of the "Invalid Transaction State" error class (25xxx) and specifically enforces PostgreSQL's constraint that all nested transactions within a parent transaction must operate at the same isolation level. Unlike the parent transaction's isolation level which is set at the BEGIN statement, subtransactions cannot have their isolation level changed independently.
Check the isolation level of your current transaction:
SHOW transaction_isolation;
-- or
SELECT current_setting('transaction_isolation');Common values are: read uncommitted, read committed, repeatable read, serializable
If you have SET TRANSACTION ISOLATION LEVEL inside a SAVEPOINT, remove it. Subtransactions inherit the parent's isolation level and cannot change it:
-- INCORRECT - Will cause error 25004
BEGIN;
SET TRANSACTION ISOLATION LEVEL SERIALIZABLE;
SAVEPOINT sp1;
SET TRANSACTION ISOLATION LEVEL REPEATABLE READ; -- Error here!
INSERT INTO table_name VALUES (...);
COMMIT;-- CORRECT - Set isolation at BEGIN, not in SAVEPOINT
BEGIN ISOLATION LEVEL SERIALIZABLE;
SAVEPOINT sp1;
INSERT INTO table_name VALUES (...);
ROLLBACK TO SAVEPOINT sp1;
COMMIT;Transaction isolation level must be set at the beginning of the transaction, before any queries or data modifications:
-- CORRECT - Set isolation level first
BEGIN;
SET TRANSACTION ISOLATION LEVEL REPEATABLE READ;
SELECT * FROM table_name; -- First query
-- Now you can create savepoints
SAVEPOINT sp1;
INSERT INTO other_table VALUES (...);
COMMIT;If you try to change isolation after the first query, you'll get an error. Set it immediately after BEGIN.
In PL/pgSQL exception blocks (which create implicit subtransactions), you cannot change isolation level:
-- INCORRECT
CREATE OR REPLACE FUNCTION problematic_func()
RETURNS void AS $$
BEGIN
-- Main transaction isolation level is already set
BEGIN
SET TRANSACTION ISOLATION LEVEL SERIALIZABLE; -- Error here!
INSERT INTO log_table VALUES ('action');
EXCEPTION
WHEN OTHERS THEN
RAISE NOTICE 'Error occurred';
END;
END;
$$ LANGUAGE plpgsql;-- CORRECT - Set isolation level before calling function
BEGIN ISOLATION LEVEL SERIALIZABLE;
SELECT problematic_func(); -- Function inherits isolation level
COMMIT;If using distributed transactions (two-phase commit), ensure all transaction branches have compatible isolation levels:
-- Correct: Both branches use same isolation level
-- Branch 1
xa_begin('branch1', ...);
SET TRANSACTION ISOLATION LEVEL REPEATABLE READ;
UPDATE table_a SET value = 1;
xa_prepare('branch1', ...);
-- Branch 2
xa_begin('branch2', ...);
SET TRANSACTION ISOLATION LEVEL REPEATABLE READ; -- Same level
UPDATE table_b SET value = 2;
xa_prepare('branch2', ...);
-- Complete both branches
xa_commit('branch1', ...);
xa_commit('branch2', ...);Choose the isolation level once at transaction start based on your needs:
-- For general transactional safety
BEGIN ISOLATION LEVEL READ COMMITTED;
-- For phantom read protection
BEGIN ISOLATION LEVEL REPEATABLE READ;
-- For serialization anomaly protection (strictest)
BEGIN ISOLATION LEVEL SERIALIZABLE;All subtransactions within will use this same level.
PostgreSQL Isolation Level Architecture: PostgreSQL only supports changing the isolation level at transaction start (before the first query/DML statement). Once any statement executes, the isolation level is locked for the transaction. Subtransactions inherit the parent's isolation level and cannot override it—this is by design to prevent serialization anomalies in nested transaction scenarios.
Serializable Snapshot Isolation (SSI): When using SERIALIZABLE isolation level, PostgreSQL uses SSI (introduced in v9.1) instead of true serializability. This provides serializable guarantees without the performance cost of traditional locking. Be aware that serializable transactions may fail with serialization errors during high concurrency, requiring retry logic.
Connection Pooler Gotchas: Connection poolers like PgBouncer in transaction pooling mode may reset session state between transactions, clearing the isolation level. Use application-level transaction management or ensure the pooler preserves transaction isolation settings.
SAVEPOINT Limitations with Isolation: While you cannot change isolation level in a SAVEPOINT, you can still use SAVEPOINT to create rollback points within a subtransaction. The isolation level applies to the entire transaction hierarchy—all SAVEPOINTs operate under the parent transaction's isolation level.
XA and Distributed Transactions: When coordinating multiple database connections in XA (distributed) transactions, all branches must agree on isolation level before preparing. Mismatched isolation levels between branches can cause prepare-phase failures and error 25004-like conditions in some database systems.
Read-Only Transactions: Combining isolation levels with read-only mode is valid and often recommended. READ ONLY transactions at SERIALIZABLE level provide the highest isolation with better performance than read-write SERIALIZABLE for analytical queries.
ERROR: syntax error at end of input
Syntax error at end of input in PostgreSQL
Bind message supplies N parameters but prepared statement requires M
Bind message supplies N parameters but prepared statement requires M in PostgreSQL
Multidimensional arrays must have sub-arrays with matching dimensions
Multidimensional arrays must have sub-arrays with matching dimensions
ERROR: value too long for type character varying
Value too long for type character varying
insufficient columns in unique constraint for partition key
How to fix "insufficient columns in unique constraint for partition key" in PostgreSQL