How to get a full trace of a prog's execution?

[kj]

I'm trying to exterminate a bug that shows up very sporadically
(but with serious results). The program in question is a CGI script
and I'm having a very hard time rooting out the bug.

It would be extremely useful to be able to toggle on something akin
to "Trace Mode" in the Perl debugger, sending the trace to some
user-specified file. (Since the bug shows up sporadically and
unpredictable, it is not practical to try to find it by using the
Perl debugger.) Is there some other way to get such Trace output?

TIA!

kj