A design and implementation of savepoints and partial rollbacks considering transaction isolation levels of SQL2

Abstract

A partial rollback of a transaction restores the state of the transaction and the database to the state in which they have been right after the savepoint to be rolled back has been established. The paper considers the correctness of savepoints and partial rollbacks. First, a savepoint sequence number is assigned to each savepoint. According to that, without generating any savepoint log record upon establishing savepoints, all the valid savepoints of a transaction can have different savepoint sequence numbers and the order of establishment of each valid savepoint can be discriminated efficiently. Second, the lock request entries of the manual duration are not deleted from the lock table as far as some savepoints which are established after the locks are requested but before the locks are released are valid. That guarantees the correctness of savepoints and partial rollbacks under the circumstances of supporting the four transaction isolation levels of SQL2. Third, the concept of the mini-savepoint that preserves the atomicity of update operations of the SQL level is extended and adopted to triggers and stored procedures. According to that, the atomicity of triggers and stored procedures is supported and the scope of savepoint names is restricted to the internal of the corresponding triggers or stored procedures.