The UPDATE
is running in transaction - it's an atomic
operation, which means that if one of the rows fails (because of unique constrain for example) it won't update any of the 5000 rows. This is one of the ACID properties of a transactional database.
Because of this the UPDATE
hold a lock on all of the rows for the entire transaction. Otherwise another transaction can further update the value of a row, based on it's current value (let's say update records set value = value * '2'). This statement should produce different result depending if the first transaction commits or rollbacks. Because of this it should wait for the first transaction to complete all 5000 updates.
If you want to release the locks, just do the update in (smaller) batches.
P.S. autocommit
controls if each statement is issued in own transaction, but does not effect the execution of a single query