Parallel Program Control Based on Hierarchically Detected Consistent Global States

Consistent Global States (CGS) detection is a costly process. If CGS are constructed using real-time timestamps, then their hierarchical detection is possible. In a hierarchical detection scheme the load of a single central monitor is distributed among a number of monitors. We show, that hierarchical CGS detection has advantages over centralized detection: it allows for on-line monitoring of larger systems and for a more effective application control based on observed CGS. Hierarchical CGS detection can be coupled with a hierarchical application control scheme for better results. Further improvement is obtained if a timeout mechanism allows unterminated local states to be used for CGS construction. Relevant algorithms and simulation results are presented and discussed.