Ladder queue: An O(1) priority queue structure for large-scale discrete event simulation

Wai Teng Tang, Rick Siow Mong Goh, Ian Li-Jin Thng

Abstract: This article describes a new priority queue implementation for managing the pending event set in discrete event simulation. Extensive empirical results demonstrate that it consistently outperforms other current popular candidates. This new implementation, called Ladder Queue, is also theoretically justified to have O(1) amortized access time complexity, as long as the mean jump parameter of the priority increment distribution is finite and greater than zero, regardless of its variance. Many practical priority increment distributions satisfy this condition including unbounded variance distributions like the Pareto distribution. This renders the LadderQ the ideal discrete event queue structure for stable O(1) performance even under practical queue distributions with infinite variance. Numerical simulations ranging from 100 to 10 million events affirm the O(1) property of LadderQ and that it is a superior structure for large-scale discrete event simulation.