Applications commonly perform repeated computations that are mostly, but not exactly, similar. If a subsequent computation were identical to the original, the operating system could improve performance via memoization, i.e., capturing the differences in program state caused by the computation and applying the differences in lieu of re-executing the computation. However, opportunities for generic memoization are limited by a myriad of differences that arise during execution, e.g., timestamps differ and communication yields non-deterministic responses. Such difference cause memoization to produce incorrect state.