PERFORMANCE OF LOCKING-BASED CONCURRENCY CONTROL SCHEMES FOR REAL-TIME DATABASE. SYSTEMS

Abstract

Data in real-time databases has to be logically and temporally consistent. The latter arises from the need to preserve the temporal validity of data items that reflect the state of the environment that is being controlled by the system. Some of the timing constraints on the transactions that process real-time data come from this need. These constraints, in turn, necessitates time-cognizant transaction processing so that transactions can be processed to meet their dead-lines. Concurrency control for real-time databases must not only maintain the logical consistency of the database but must also allow the transactions to meet their timing constraints. Concurrency control in database systems has been examined by many people and several concurrency control schemes have been proposed. The most popular schemes are two-phase locking and optimistic schemes. For real-time environment these schemes must be augmented with a priority based conflict resolution to ensure that higher priority transactions are not delayed by lower priority transactions. In this work we study the performance of the following three locking-based protocols, using the 2PL as the underlying technique, for real.-time databases. ( 1) Priority Abort (PA). (2) Priority Inheritance (PI). (3) Conditional Priority Inheritance (CP). The PA scheme eliminates the need for a high priority transaction to have to wait for a low priority transaction. The PI scheme aims at conserving the resources by trying to eliminate the need for transaction aborts, and at the same time it tries to reduce the blocking time of high priority transactions. The third scheme which is a combination of the above two schemes attempts to capitalise the advantages of the other two.