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 correct-ness and data currency issues. The widely used two-phase locking protocol (2PL) processes the transac-tions without any correctness and data currency issues. However, the performance of 2PL deteriorates with data contention. Snapshot isolation (SI)-based pro-tocols proposed in the literature improve the perfor-mance of ROTs, but they compromise on correctness and data currency issues. Speculative locking (SL) protocols are proposed in the literature for improv-ing the performance of ROTs by carrying out spec-ulative executions only for ROTs and following 2PL for update transactions. In SL-based protocols, up-date transactions are blocked if they conflicting with ROTs. In this paper, we have proposed an improved approach to improve parallelism among update trans-actions 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 “com-pensatability ” property of ROTs and speculation. The simulation results show that the proposed protocol im-proves the performance by carrying out less number of speculative executions. Further, the proposed protocol does not violate serializability criteria.