A Semantics-Integrated Concurrency Control In Object-Oriented Databases

In the recent years, object-oriented databases(OODBs) are used in many advanced applications. OODBs are collections of classes and instances of these classes. In OODBs, both classes and instances are referred to as objects. One of the important characteristics of database systems is manipulation of shared data. That is, database systems, including OODBs, allow shared data to be accessed by multiple users at the same time. A concurrency control involves synchronization of accesses to the database so that the consistency of the database is maintained. Due to the complexity in OODBs, concurrency controls in OODBs are more complicated than those in conventional databases. The complexity in concurrency controls should not degrade the performance of OODBs. That is, concurrency controls in OODBs must keep performance while meeting the database consistency requirements. In order to have good performance, a concurrency control is designed to increase the concurrency among methods so that more transactions can run in parallel,and besides,it is to reduce the locking overhead.To solve the problem of relation of concurrency and locking overhead, by introducing direct access vector, run-time information and semantics commutativity, we give a scheme of combining semantics commutativity and the two fornamed. The scheme in the article improves the concurrency between instance access methods in object-oriented databases, and reduces the locking overhead. The lock demanders can obtain locks earlier. The model of nested transactions is introduced, which is combined with nested methods invocation in a locking scheme, and we try to give a total locking mechanism integrating the locking of the access methods on single class and class hierarchy.