FAULT TOLERANT DEADLOCK DETECTION IN DISTRIBUTED DATABASE SYSTEMS.

The availability of distributed databases is directly affected by the timely detection and resolution of deadlocks. Consequently, mechanisms are needed to make deadlock-detection algorithms resilient to failures. A new distributed deadlock-detection algorithm (DDDA) which uses a global detector to detect global deadlocks and local detectors to detect local deadlocks is presented. The algorithm essentially identifies transaction-resource interactions that may cause global (multisite) deadlocks. Such interactions are reported to the global controller, while the remaining interactions are handled locally. In order to make the DDDA fault-tolerant, three procedures have been incorporated to handle failures of the controller, local sites, and communication links. This enhanced algorithm, called FTDDDA, improves the overall performance of the database system by improving resiliency of the deadlock-detection service.