This paper presents an overview of an external state management system that has been designed and developed as part of Jade's implementation of Time Warp. The saving of state information can be a serious overhead for optimistic synchronization mechanisms. This can become particularly relevant on the critical path of a parallel simulation. One optimization possible when processes have large states is to limit state saving to those parts that change at a given event. A backtrail of state changes is maintained instead of making full state copies to support rollback. An approach to this optimization, called demand state saving (DSS) has been implemented within Jade's external state management system (ESM). ESM enables building custom state managers, such as DSS, for different types of state information. These state managers reside outside of the Time Warp executive making it easier to develop and utilize alternative state management schemes. Both ESM and DSS are described in this paper. A rough analysis that compares DSS with copy state saving suggests that in the worst case, DSS will be superior when the fraction of state modified at an event is less than 20% of the total state.
['Brian W. Unger', 'John G. Cleary', 'Alan Covington', 'Darrin West']
An external state management system for optimistic parallel simulation