The purpose of closed, nested
transactions (subtransactions) is to let a series of database operations within a transaction appear as a unit with regard to modifications to the database.Subtransactions are preceded by SUBTRANS BEGIN and closed by SUBTRANS END or SUBTRANS ROLLBACK.
SUBTRANS END and SUBTRANS ROLLBACK do not affect locks. These are only released by COMMIT or ROLLBACK. COMMIT or ROLLBACK implicitly close all subtransactions.
See also:
SUBTRANS statement COMMIT statement ROLLBACK statement