You can identify important states within a transaction and return to them selectively using savepoints to separate groups of related statements.

A SAVEPOINT statement defines an intermediate point during a transaction. You can undo all changes after that point using a ROLLBACK TO SAVEPOINT statement. Once a RELEASE SAVEPOINT statement has been executed or the transaction has ended, you can no longer use the savepoint. Note that savepoints do not have an effect on COMMITs. When a COMMIT is executed, all changes within the transaction are made permanent in the database.

No locks are released by the RELEASE SAVEPOINT or ROLLBACK TO SAVEPOINT commands: locks are released only at the end of a transaction.

 Naming and nesting savepoints