Using execution logs for improving Pseudo-Boolean propagation

Among all procedures that CDCL-based SAT solvers implement, unit propagation dominates the total running time. Hence, it is not a surprise that large research efforts have been invested on improving it. As a result, the two-watched-literal scheme, enhanced with implementation details boosting its performance, emerged as the dominant method. The importance of unit propagation in pseudo-Boolean solvers is similar. However, no dominant method exists: counter and watch-based propagation are well-suited for different types of constraints, opening the door to hybrid methods. The higher complexity of implementing pseudo-Boolean solvers has shifted the research focus to higher-level aspects of other procedures, considering implementation details of unit propagation not a priority. In this paper, we first present execution logs: a novel methodology that allows us to precisely evaluate the performance of different propagation procedures. Secondly, we show how both counter and watch-based propagation routines in the RoundingSat solver can be largely improved thanks to a careful analysis of various implementation issues. Thirdly, a detailed analysis shows that hybrid methods outperform the ones based on a single technique. Finally, our experiments reveal that improvements in propagation lead to a clearly better overall performance of the solver.