Distributed Optimistic Concurrency Control for High Performance Transaction Processing

The performance of high-volume transaction processing systems is determined by the degree of hardware and data contention. This is especially a problem in the case of distributed systems with glob~! transactions accessing and updating objects from multiple systems. While the conventional two-phase locking method 11f centralized systems can be adapted for concurrency control in distributed systems, it may restrict system throughput to very low levels. This is due to ~ significant increase in lock holding times and associated transaction waiting time for locks, as compared to centralized systems. Optimistic concurrency control (OCC) which is similarly extensible to distributed systems has the disadvantage of repeated transaction restarts, which is a weak point of currently proposed methods. We propose a new hybrid method based on OCC followed by locking, which is an integral part of distributed validation and two-phase commit. This new OCC method assures that a transaction failing its validation will not be reexecuted more than once, in general. Furthermore deadlocks, which are difficult to handle in a distributed environment, arc avoided by serializing lock requests. We outline implementation details and compare the performance of the new scheme with distributed two-