Analysis of concurrency—coherency control protocols for distributed transaction processing systems with regional locality

Abstract

In this paper we examine a system structure and protocols to improve the performance of a distributed transaction processing system when there is some regional locality of data reference. Several transaction processing applications such as reservation systems, insurance, and banking belong to this cate-gory. While maintaining a distributed computer system at each region, a central computer system is introduced with a replication of all databases at the distributed sites. It can provide the advantage of distributed systems for transactions that refer principally to local data, and also can provide the advantage of centralized systems for transactions accessing nonlocal data. Specialized protocols can be designed to keep the copies at the distributed and centralized systems consistent without incurring the overhead and delay of generalized protocols for fully replicated databases. In this paper we study the advantage achievable through this system structure and the trade-offs between protocols for concurrency and coherency control of the duplicate copies of the databases. An approximate analytic model is employed to estimate the system performance. It is found that the performance is indeed sensitive to the protocol and substantial performance improvement can be obtained as compared with distributed systems. The protocol design factors considered include the approach for intersite concurrency control (optimistic versus pessimistic), resolution of aborts due to intersite conflict, and choice of the master/primary site of the dual copies (distributed site versus central site). Among the protocols considered, the most robust one uses an optimistic protocol for intersite control with the distributed site as the master site, allows a locally running transaction to commit without any communication with the central site, and balances transaction aborts between transactions running at the central site and distributed sites. © 1992 IEEE