Hi thanks for your interest in Retrace. Currently the way Retrace works means that if you change the code, the replay will likely diverge. This extends to logging statements. The ability to adapt code to allow for what-if reasoning is somethign we're looking at but not currently supported. But I would ask why would you want to? Retrace allows full forward/backwards debugging of execution runs. With this capability what would adding log statements to the replay give you? In terms of performance instrumentation, with no breakpoints the replay will ruin at full speed with no IO wait. You could profile the replay and get a really accurate idea of where the CPU bottlenecks are. Hope this helps answer your questions.