Abstract

Abstract. Conflict-driven constraint learning provides big gains on many CSP and SAT problems. However, time and space costs to propagate the learned constraints can grow very quickly, so constraints are often discarded (forgotten) to reduce overhead. We conduct a major empirical investigation into the overheads introduced by unbounded constraint learning in CSP. This is the first such study in either CSP or SAT. We obtain two significant results. The first is that a small percentage of learnt constraints do most propagation. While this is conventional wisdom, it has not previously been the subject of empirical study. Second, we show that even constraints that do no effective propagation can incur significant time overheads. Finally, by implementing forgetting, we confirm that it can significantly improve the performance of modern learning CSP solvers, contradicting some previous research. 1

Citations