Xdebug's built-in garbage collection statistics profiler allows you to find out when the PHP internal garbage collector triggers, how many variables it was able to clean up, how long it took, and how how much memory was actually freed.
The most important and obvious difference between TTD and rr is that TTD is for Windows and rr is for Linux (though a few crazy people have had success debugging Windows applications in Wine under rr).
TTD supports recording of multiple threads in parallel, while rr is limited to a single core.
當然,更完整的錄影也是要付出效能代價的:
On the other hand, per-thread recording overhead seems to be much higher in TTD than in rr. It's hard to make a direct comparison, but a simple "start Firefox, display mozilla.org, shut down" test run on similar hardware takes about 250 seconds under TTD and 26 seconds under rr.