AD- 251 925EONS ON SOFTWARE ENGINEERI[NG_ _ AD-A251 925 ososo, = OPTIMISTIC EXECUTION AND CHECKPOINT COMPARISON FOR ERROR RECOVERY IN PARALLEL AND DISTRIBUTED SYSTEMS'

This paper describes a checkpoint comparison and optimistic execution technique for error detection and recovery in distributed and parallel systems. The approach is based on lookahead execution and rollback validation. It uses replicated tasks executing on different processors for forward recovery and checkpoint comparison for error detection. Two schemes derived from this strategy are analyzed and compared with triplication and voting, and with two common backward recovery methods. The impact of checkpoint time, checkpoint validation time. and process restart time is also examined. An implementation on a Sun NFS network with six benchmark programs is presented. Compared with classic checkpointing and rollback techniques, our strategy provides rapid recovery and requires, on average, fewer processors than standard replication and voting methods. This strategy is useful in systems where spare processors are available at the time of recovery. Key Words: fault tolerant computing, checkpointing, error detection, and error re-covery. [This docurnent has been approved fo public release and sale; its distribution is unlimited