Aspects of an application program's execution which might be subject to non-determinism are performed in a deterministic manner while the application program's execution is being recorded in a virtual machine environment so that the application program's behavior, when played back in that virtual machine environment, will duplicate the behavior that the application program exhibited when originally executed and recorded. Techniques disclosed herein take advantage of the recognition that only minimal data needs to be recorded in relation to the execution of deterministic operations, which actually can be repeated “verbatim” during replay, and that more highly detailed data should be recorded only in relation to non-deterministic operations, so that those non-deterministic operations can be deterministically simulated (rather than attempting to re-execute those operations under circumstances where the outcome of the re-execution might differ) based on the detailed data during replay.