Chronological Backtracking

Alexander Nadel, Vadim Ryvchin

Abstract: Non-Chronological Backtracking (NCB) has been implemented in every modern CDCL SAT solver since the original CDCL solver GRASP. NCB’s importance has never been questioned. This paper argues that NCB is not always helpful. We show how one can implement the alternative to NCB–Chronological Backtracking (CB)–in a modern SAT solver. We demonstrate that CB improves the performance of the winner of the latest SAT Competition, Maple_LCM_Dist, and the winner of the latest MaxSAT Evaluation Open-WBO.