Optimistic Replication with Forward Conflict Resolution in Distributed Real-Time Databases

Sammanfattning: In this thesis a replication protocol – PRiDe – is presented, whichsupports optimistic replication in distributed real-time databases withdeterministic detection and forward resolution of transaction conflicts. Theprotocol is designed to emphasize node autonomy, allowing individualapplications to proceed without being affected by distributed operation. Forconflict management, PRiDe groups distributed operations into generationsof logically concurrent and potentially conflicting operations. Conflictsbetween operations in a generation can be resolved with no need forcoordination among nodes, and it is shown that nodes eventually convergeto mutually consistent states. A generic framework for conflict resolutionis presented that allows semantics-based conflict resolution policies andapplication-specific compensation procedures to be plugged in by thedatabase designer and application developer.It is explained how transaction semantics are supported by the protocol,and how applications can tolerate exposure to temporary databaseinconsistencies. Transactions can detect inconsistent reads and compensatefor inconsistencies through callbacks to application-specific compensationprocedures. A tool – VADer – has been constructed, which allows databasedesigners and application programmers to quickly construct prototype applications,conflict resolution policies and compensation procedures. VADercan be used to simulate application and database behavior, and supportsrun-time visualization of relationships between concurrent transactions.Thus, VADer assists the application programmer in conquering the complexityinherent in optimistic replication and forward conflict resolution.