Extending Speculation to Process Distributed Read-Only Transactions (ROTs) and Analysis of Semantics-based ROTs Processing Protocol with Benchmarks

In the internet environment, computers-based information systems are being employed to maintain large amounts of information to meet different users’ information requirements. The users interact with the system by inserting/updating/querying the required information. The information systems process the user requests by executing the update transactions (UTs) for inserts/updates and readonly transactions (ROTs) for queries. An ROT contains only read operations whereas an UT contains both read and update operations. Processing of ROTs in a correct and efficient manner is a research issue. Efforts are being made in the literature to propose improved approaches. The main issues in processing ROTs are correctness (serializability), ensuring data currency and high performance. Even though the popular two-phase locking (2PL) protocol processes ROTs correctly with no data currency related issues, its performance deteriorates with data contention. Snapshot-based algorithms have been proposed to improve the performance by compromising both data currency and correctness aspects. Recently, two speculative locking-based (SL-based) approaches have been proposed in literature for improving the performance of ROTs. In these protocols, UTs are processed with 2PL and ROTs are processed with SL. One is synchronous SL-based approach in which speculative executions are carried out in synchronous manner and another is asynchronous SL-based approach in which speculative executions are carried out in asynchronous manner. Overall, the SL-based protocols for ROTs improve the performance without compromising both correctness and data currency. However, the SL-protocols follow 2PL to process UTs. Under SL-protocols UTs are blocked if they conflict with ROTs. Semantics-based protocols have been proposed in the literature for improving the performance without blocking UTs if they conflict with ROTs. The notion of compensability of ROTs is being exploited to improve the concurrency. So, the SL-based approached have been proposed by considering centralized database environment. In this thesis, we have extended SL-based approaches for processing ROTs in distributed database system (DDBS). In addition, we have analyzed the performance of semantics-based protocols by considering TPC-C and TPC-W benchmarks. We have extended both synchronous SL-based as well as asynchronous SL-based locking, protocols to process ROTs in DDBS. While extending SL-based protocols, it has been identified that an ROT under SL-based protocols requires an additional commit phase and requires single round of communication. In addition it has been found out that, additional messages are required for making speculative versions available to ROTs during the execution phase of an update transaction. In spite of these overheads, the performance results show that the proposed protocols significantly improve the performance over 2PL and SI-based protocols. Similar to centralized case, the proposed protocols do not compromise both correctness and data currency aspects. The analysis of semantics-based protocol with TPC-C and TPC-W benchmarks has been carried out by identifying various types of conflicts among the pair of transactions in both benchmarks. The analysis showed that six out of the eleven cases are compensatable in TPC-C and eleven out of twelve UT-ROT conflicts are compensatable in TPC-W. The analysis indicates that semanticsbased protocol has a potential to improve the performance in a realistic scenario.