A FAMILY OF HIERARCHICAL CONCURRENCY CONTROL PROTOCOLS

In this thesis, we propose a family of concurrency control protocols for high data contention database environments. The first one is called the Prudent-Precedence Concurrency Control (PPCC) protocol. It is prudently more aggressive in permitting more serializable schedules than two-phase locking and maintains a restricted precedence among conflicting transactions and commits the transactions according to the serialization order established in the executions. The second one is a family of hierarchical concurrency control protocols called the Hierarchical Precedence Concurrency Control (HPCC) protocols. It maintains cycle-free precedence hierarchies for conflicting transactions. Conflicting operations are allowed to proceed only if the hierarchical orderings of precedence is not violated. Transactions also commit based on the serialization order established during the executions. Detailed simulation models have been implemented for all these protocols and extensive experiments have been conducted to evaluate the performance of the proposed approaches. The results demonstrate that the proposed algorithms outperform the two-phase locking and optimistic concurrency control over a wide range of system workloads