Sequential and Parallel Algorithms for Frontier A* with Delayed Duplicate Detection

We present sequential and parallel algorithms for Frontier A* (FA*) algorithm augmented with a form of Delayed Duplicate Detection (DDD). The sequential algorithm, FA*-DDD, overcomes the leak-back problem associated with the combination of FA* and DDD. The parallel algorithm, PFA*-DDD, is a parallel version of FA*-DDD that features a novel workload distribution strategy based on intervals. We outline an implementation of PFA*-DDD designed to run on a cluster of workstations. The implementation computes intervals at runtime that are tailored to fit the workload at hand. Because the implementation distributes the workload in a manner that is both automated and adaptive, it does not require the user to specify a workload mapping function, and, more importantly, it is applicable to arbitrary problems that may be irregular. We present the results of an experimental evaluation of the implementation where it is used to solve instances of the multiple sequence alignment problem on a cluster of workstations running on top of a commodity network. Results demonstrate that the implementation offers improved capability in addition to improved performance.