Fast-software-checkpointing in optimistic simulation: embedding state saving into the event routine instructions

We present a software approach, namely fast-software-checkpointing (FSC), to reduce the running time of the state saving protocol in optimistic parallel discrete event simulation. The idea behind FSC is to use the instructions performed during the execution of an event as part of the state saving protocol, hence the total number of instructions due to state saving is reduced. Under FSC the time for saving the state of a logical process prior to the execution of an event E requires an amount of time proportional to the amount of state variables not updated by E's execution, as only these variables must be copied. This outlines that FSC shows some dualism with respect to incremental state saving. We show, however that there exists a basic difference between the two solutions as in FSC some of the state saving instructions are actually event routine instructions, while in incremental state saving they are only added and mixed to the latter ones. We also present a simple software architecture to support FSC and simulation results to demonstrate the effectiveness of such solution. The obtained data show that FSC, combined with a sparse state saving strategy may represent the best checkpointing solution in case of both medium/small state granularity simulations and large state granularity simulations even with small (but non-minimal) portions of the state updated by event execution. FSC may result therefore suited for a wide class of simulation problems.