Revisiting Commit Processingindistributed

A signi cant body of literature is available on distributed transaction commit protocols. Surprisingly, however, the relative merits of these protocols have not been studied with respect to their quantitative impact on transaction processing performance. In this report, using a detailed simulation model of a distributed database system, we pro le the transaction throughput performance of a representative set of commit protocols. A new commit protocol, OPT, that allows transactions to \optimistically" borrow uncommitted data in a controlled manner is also proposed and evaluated. The new protocol is easy to implement and incorporate in current systems, and can coexist with most other optimizations proposed earlier. For example, OPT can be combined with current industry standard protocols such as Presumed Commit and Presumed Abort. The experimental results show that distributed commit processing can have considerably more in uence than distributed data processing on the throughput performance and that the choice of commit protocol clearly a ects the magnitude of this in uence. Among the protocols evaluated, the new optimistic commit protocol provides the best transaction throughput performance for a variety of workloads and system con gurations. In fact, OPT's peak throughput is often close to the upper bound on achievable performance. Even more interestingly, a three-phase (i.e., nonblocking) version of OPT provides better peak throughput performance than all of the standard two-phase (i.e., blocking) protocols evaluated in our study. 1