Semantic Concurrency Control in Distributed Object-Oriented Database-Systems.

摘要

The paper presents a new locking protocol for distributed object-oriented database systems (OODBSs). The protocol can exploit the semantics of methods that are invoked on encapsulated objects. Compared to conventional page-oriented or record-oriented concurrency control protocols, the developed protocol greatly improves concurrency because commutative method executions on the same object are not considered as a conflict. Unlike previous work on concurrency control for abstract data types (ADTs), the protocol takes care of the fact that ADTs can be implemented in terms of other ADTs. To ensure that each method of execution appears as an indivisible action, the dynamic method invocation hierarchies that result from transaction executions are treated as open nested transactions. The locking protocol ensures 'semantic serializability' with respect to the methods that are invoked as top-level actions. The developed locking protocol deals with the following additional problem that arises in OODBSs. A method on an object can be invoked at arbitrary levels in the transaction tree, that is, directly as a top-level action or indirectly to implement another method on another or the same object. The developed locking protocol solves this problem by considering the ancestors of conflicting method invocations in the processing of lock requests.