Optimistically synchronized parallel discrete-event simulation is based on the use of communicating sequential processes. Optimistic synchronization means that the processes proceed under the assumption that a synchronized execution schedule is fortuitous. Periodic checkpointing of the state of a process allows the process to roll back to an earlier state when synchronization errors are detected . This paper examines the effects of varying the checkpoint interval on the execution time and memory space needed to perform a parallel simulation.The empirical results presented in this paper were obtained from the simulation of closed stochastic queueing networks with several different topologies. Various intra-processor process scheduling algorithms and both lazy and aggressive cancellation strategies are considered . The empirical results are compared with analytical formulae predicting time-optimal checkpoint intervals. Two modes of operation, throttling and thrashing have been noted and their effect examined. As the checkpoint interval is increased from one, there is a throttling effect among processes on the same processor which improves performance. When the checkpoint interval is made too large, there is a thrashing effect caused by interaction between processes on different processors. It is shown that the time-optimal and space-optimal checkpoint intervals are not the same. Furthermore, a checkpoint interval that is too small adversely affects space more than time; whereas, a checkpoint interval that is too large adversely affects time more than space.
Copyright 1993 by Association for Computing Machinery, Inc.
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Copyright 2002 by Bruno R. Preiss, P.Eng. All rights reserved.
Tue Jan 1 13:41:25 EST 2002