[greglaw99]

Have you ever used time-travel debugging? Core dumps give you a backtrace (assuming stack is sane) which gives some clue of how I got here, but not _why_ I got here. e.g. assertion failure. I wrote that assertion because I believed this thing would always be true. Now I find it is not true. From a corefile I can't usually see why it not true.

With a time travel recording I can put a watchpoint (aka data breakpoint) on the state that is supposedly impossible, and reverse-continue back to see exactly where it got set. (And repeat as required.) It really is very powerful.

Admittedly there are situations in which it's not practical to get a recording, but when you can... almost any bug becomes trivial.