Dynamic slicing long running programs through execution fast forwarding

Fixing runtime bugs in long running programs using trace based analyses such as dynamic slicing was believed to be prohibitively expensive. In this paper, we present a novel execution fast forwarding technique that makes this feasible. While a naive solution is to divide the entire execution by checkpoints, and then apply dynamic slicing enabled by tracing to one checkpoint interval at a time, it is still too costly even with state-of-the-art tracing techniques. Our technique is derived from two key observations. The first one is that long running programs are usually driven by events, which has been taken advantage of by checkpointing/replaying techniques to deterministically replay an execution from the event log. The second observation is that all the events are not relevant to replaying a particular part of the execution, in which the programmer suspects an error happened. We develop a slicing-like technique that can be used to prune irrelevant events from the event log. Driven by the reduced log, the replayed execution is now traced for fault location. This replayed execution has the effect of fast forwarding, i.e the amount of executed instructions is significantly reduced without losing the accuracy of reproducing a failure. Our evaluation shows that skipping irrelevant events can reduce the space requirement for dynamic slicing by factors ranging from 72 to 44490. We also describe how checkpointing and tracing enabled dynamic slicing are combined, which we believe is the first attempt to integrate these two techniques. Finally, the dynamic slices of a set of reported bugs for long running programs are studied to show the effectiveness of dynamic slicing.