Design Issues for Extensible Concurrency Control Mechanisms

Relational database management systems lack the requisite support for specialized applications such as engineering databases, electronic design databases, geographic databases, etc. Extensible database management systems attempt to ll this void by providing capabilities to deene query language extensions and specialized storage structures that suit the particular application. However, they do not provide for having multiple concurrency control policies operating simultaneously. This feature appears useful for multi-application workloads since it would be best, from a performance viewpoint, if each application operated under its favourite concurrency control algorithm. The problem, however, is to maintain database integrity in this environment. In this paper, we address the issue of designing mechanisms that allow extensible database systems to simultaneously operate multiple concurrency control policies without loss of data integrity. The key properties of such a mechanism are: Firstly, to ensure extensibility, the mechanism must be independent of the actual concurrency control policies that are co-existent. More generally, it must be able to support any concurrency control policy that adheres to a standard interface. Secondly, the mechanism must minimize the interference between the individual concurrency control policies to ensure that the performance of the individual applications remains good. We present here a database system architecture that attempts to satisfy both these requirements. Preliminary results from a simulation-based study of this architecture indicate promising performance trends.