Precision locks

ABSTRACT

This paper describes a new method for controlling data base concurrency, called precision locks (PL). The name is derived from the fact that they lock precisely the set of tuples required to guarantee data base consistency, phantoms included. This results in maximum concurrency among all tuple-level locking methods, including predicate locks. A framework for comparing locking systems which indicates the errors committed by them is introduced. It is shown that existing systems commit these errors while PL does not. While other logical locking systems are limited in the complexity of permissible predicates, PL allows them to be arbitrary. It is shown that transactions under PL are well formed and two phased which is sufficient to maintain consistency. The execution cost of PL is compared to a conventional tuple-level locking method. It is found that PL usually is cheaper to execute.

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