Lock Conversions Two-phase locking with lock conversions: First Phase: can acquire a lock-S on item can acquire a lock-X on item can convert a lock-S to a lock-X(upgrade) Second Phase: can release a lock-S can release a lock-X can convert a lock-X to a lock-S (downgrade) This protocol assures serializability.But still relies on the programmer to insert the various locking instructions. Database System Concepts-5th Edition,Oct 5,2006 16.11 ©Silberschat乜，Korth and SudarshanDatabase System Concepts - 5 16.11 ©Silberschatz, Korth and Sudarshan th Edition, Oct 5, 2006 Lock Conversions Two-phase locking with lock conversions: – First Phase: can acquire a lock-S on item can acquire a lock-X on item can convert a lock-S to a lock-X (upgrade) – Second Phase: can release a lock-S can release a lock-X can convert a lock-X to a lock-S (downgrade) This protocol assures serializability. But still relies on the programmer to insert the various locking instructions