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A priority queue is a fundamental data structure that maintains a dynamic set of (key, priority)-pairs and supports Insert, Delete, ExtractMin and DecreaseKey operations. In the external memory model, the current best priority queue supports each operation in amortizedOs. If the DecreaseKey operation does not need to be supported, one can design a more efficient data structure that supports the Insert, Delete and ExtractMin operations in O( 1 B log N B / log M B ) I/Os. A recent result shows that a degradation in performance is inevitable by proving a lower bound of Ω( 1 B log B/ log log N ) I/Os for priority queues with DecreaseKeys. In this paper we tighten the gap between the lower bound and the upper bound by proposing a new priority queue which supports the DecreaseKey operation and has an expected amortized I/O complexity of O( 1 B log N B / log log N ). Our result improves the external memory priority queue with DecreaseKeys for the first time in over a decade, and also gives the fastest external memory single source shortest path algorithm.

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