Short Notes: On the Heterogeneous Guard Locking Protocol
Gael N. Buckley · The Computer Journal · 1984
The heterogeneous guard locking protocol is a general non-two-phase locking protocol that is applicable to database systems organized as rooted directed acyclic graphs. The protocol is one of the few serializable protocols that employs both shared and exclusive locks and yet remains deadlock free. In this note we present the protocol and prove that it ensures freedom from deadlock. This in turn implies that consistency of the database can be maintained without resorting to transaction rollback.