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

A system structure and protocols for improving the performance of a distributed transaction processing system when there is some regional locality of data reference are presented. A distributed computer system is maintained at each region, and a central computer system with a replication of all databases at the distributed sites is introduced. It provides the advantage of distributed systems principally for local transactions, and has the advantage of centralized systems for transactions accessing nonlocal data. Specialized protocols keep the copies at the distributed and centralized systems consistent without incurring the overhead and delay of generalized protocols for fully replicated databases. The advantages achievable through this system structure and the tradeoffs between protocols for concurrency and coherency control of the duplicate copies of the databases are studied. An approximate analytic model is used to estimate the system performance. It is found that the performance is sensitive to the protocol and that substantial performance improvement can be obtained as compared with distributed systems