Exploiting Semantics and Speculation for Improving the Performance of Read-only Transactions

A read-only transaction (ROT) does not modify any data. Efforts are being made in the literature to improve the performance of ROTs without correctness and data currency issues. The widely used twophase locking protocol (2PL) processes the transactions without any correctness and data currency issues. However, the performance of 2PL deteriorates with data contention. Snapshot isolation (SI)-based protocols proposed in the literature improve the performance of ROTs, but they compromise on correctness and data currency issues. Speculative locking (SL) protocols are proposed in the literature for improving the performance of ROTs by carrying out speculative executions only for ROTs and following 2PL for update transactions. In SL-based protocols, update transactions are blocked if they conflicting with ROTs. In this paper, we have proposed an improved approach to improve parallelism among update transactions and ROTs by exploiting a new notion called “compensatability”. In this protocol, an ROT which can be “compensatable” can complete the execution and carry out compensating operation to incorporate the effect of conflicting update transactions. As a result, the parallelism is improved over SL protocols as the update transactions which are conflicting with ‘compensatable’ ROTs need not block. In this paper, we have proposed a protocol by exploiting both “compensatability” property of ROTs and speculation. The simulation results show that the proposed protocol improves the performance by carrying out less number of speculative executions. Further, the proposed protocol does not violate serializability criteria.