The performance of parallel Prolog programs

Performance results are presented for a parallel execution model for PROLOG that supports AND-parallelism, OR-parallelism, and intelligent backtracking. The results show that restricted AND-parallelism is of limited benefit for small programs, but produced speedups from 7-10 on two large programs. OR-parallelism was found to be generally not useful for the benchmarks examined if the semantics of PROLOG were preserved. Of particular interest is the phenomenon of supermultiplicative behavior, in which the performance improvement obtained when more than one technique is used is greater than the product of the performance improvements due to each technique individually. The implications of the performance results for parallel PROLOG systems are discussed, and directions for future work are indicated. (I.E.)