We present Oolong, a distributed programming framework designed for sparse asynchronous applications such as distributed web crawling, shortest paths, and connected components. Oolong stores program state in distributed in-memory key-value tables on which user-defined triggers may be set. Triggers can be activated whenever a key-value pair is modified. The event-driven nature of triggers is particularly appropriate for asynchronous computation where workers can independently process part of the

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... state towards convergence without any need for global synchronization. Using Oolong, we have implemented solutions for several large-scale asynchronous computation problems, achieving good performance and robust fault tolerance.