On Non-Intrusive Workload-Aware Database Replication

Performance and high-availability are the crucial factors in the development of nowadays distributed database systems. Both of these challenges are commonly addressed by means of the same technique, database replication. The overall throughput of the system is increased by leveraging parallel computation on different sites, and in case of replica failures, availability is improved by redirecting requests to operational replicas. However, providing transparent database replication is not an easy task. Although database replicas should be as independent of each other as possible for performance and availability reasons, some synchronization is required to provide data consistency. This thesis is about non-intrusive (or middleware) database replication protocols. More specifically, this thesis focuses on the development of practical replication protocols that use off-the-shelf database engines, take advantage of group communication primitives, cope with failures of system components, behave correctly, and, by exploiting the specific characteristics of the application, achieve high performance. In the first part of this thesis we address the following problem: non-intrusive database replication protocols cannot obtain fine-grained information about transactions due to limited access to the database engine internals. We make three contributions in this part. The first contribution is the Multiversion Database State Machine, a middleware extension of the Database State Machine, a kernelbased replication approach. The Multiversion Database State Machine assumes predefined, parameterized transactions. The particular data items accessed by a transaction depend on the transaction’s type and the parameters provided by the application program when the transaction is instantiated. The second contribution of this thesis is a technique to bypass the extraction and propagation of readsets and writesets in non-intrusive replication protocols. We present the SQL Inspector, a tool capable to automatically identify conflicting transactions before their actual execution by partially parsing them. The performance of the Multiversion Database State Machine can be further improved if transactions execute at carefully chosen database sites. Thus, the third contribution of this thesis is