Adding PEP to real-time distributed commit processing

Abstract

One-phase commit protocols substantially reduce the overheads of transaction commit processing, making them attractive for incorporation in distributed real-time databases. A major obstacle, however is that these protocols significantly increase the occurrence of priority inversions. This arises from the cohorts of each distributed transaction being in a prepared state for extended periods of time, during which their data locks cannot be pre-empted. We present a new one-phase real-time commit protocol, called PEP (short for PROMPT-EP, where PROMPT = “Permits Reading Of Modified Prepared-data for Timeliness”, which is a real-time commit protocol, and EP = “Early Prepare”, which is a one-phase commit protocol). PEP addresses the above-mentioned problem by suitably utilizing our previously proposed prepared data-borrowing technique. A simulation-based evaluation of PEP for real-time applications with firm deadlines demonstrates that, for a variety of environments, it substantially reduces the number of killed transactions as compared to its multi-phase counterparts. In fact, PEP often provides better performance than even an equivalent centralized system.