Conservative vs. optimistic parallel simulation of DEVS and Cell-DEVS: a comparative study

The conservative Parallel DEVS protocol offers a novel approach that allows conservative simulation of DEVS-based PDES systems. The protocol is based on the classical Chandy-Misra-Bryant synchronization mechanism, and it extends the DEVS abstract simulator to provide means for lookahead computation and null-messages. We present a purely conservative simulator, called CCD++, designed for running large-scale DEVS and Cell-DEVS models in parallel and distributed fashion. A comparative performance analysis is presented, analyzing the performance of CCD++ compared to an optimistic DEVS simula-tor. Several DEVS-based environmental models with different characteristics are studied. The experiments indicate that the conservative simulator improves performance in terms of execution time, memory usage, operational cost, and system stability for very large models. 1. INTRODUCTION Many studies have been carried out to show the differences between parallel synchronization mechanisms. Conservative and optimistic approaches are the two major classes of parallel synchronization techniques proposed for parallel discrete event simulation (PDES). Conservative synchronization [1] has more limited parallelism when compared to optimistic algorithms. Conservative approaches strictly avoid causality violations while optimistic approaches [2] allow violations and recover from them by providing a rollback mechanism (which is more costly in rollback and state saving overhead). The Chandy-Misra-Bryant (CMB) [3,4] conservative mechanism prevents deadlocks by introducing null-messages and the notion of lookahead. We are interested in combining advanced parallel simulation algorithms for large scale simulations. We want to combine the formal advantages of the DEVS