Optimizing for the non-failure case does not mean that the ramifications on commit processing due to failure is not of any interest. The reliability aspect of commit processing is extremely important and we could not considered our work fundamentally complete without studying the impact of commit failures in various environments. Heuristic decisions (HD) and their effect on 2PC reliability have been little addressed in the literature but they are considered a practical necessity in the commercial environment. This part of my work argued the importance of incorporating heuristics decisions in commit protocols and studied the effect of doing so. It provided a comprehensive study of heuristics decisions: how and when they occur, how they are process, and the importance of being identified and effectively reported to the transaction or commit initiator. It studied how commit protocols are affected and proposed a 2PC protocol variant, called Presumed Nothing (PrN), that effectively handles heuristic decisions. It described how certain commit optimizations can be used to tune the variant's performance around application requirements, and presented an appropriate commit programming interface. Finally, we studied the effect of adding HD to the main commit variations, such as PA, PC and IBM-PN showing that all collapse (almost) to the PrN.

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