From: Ron M <rm_rails@...>
Date: 2005-11-05T10:24:22+09:00
Subject: Re: Getting a stack trace of a running Ruby program.

Robert Klemme wrote:
> Ron M <rm_rails@cheapcomplexdevices.com> wrote:
> 
>> Is there a way of displaying the stack trace of a running ruby
>> [like] Java  QUIT signal
>> [or] the "pstack" program gives you the same capabilities for C programs.
> 
> I prefer to use real profiling tools instead of looking at a single 
> stacktrace.  In Java that would be -Xrunhprof, OptimizeIt et al.  In 
> Ruby you can use -r profile for profiling.  Also, there's module 
> Benchmark which is less intrusive than the profiler.  Finally there's 
> set_trace_func which can be used to generate call stacks for each thread 
> and print them to console on a signal similarly to your Java approach.
> 
> HTH

These all work fine for relatively short-lived programs; but
do little to help in a progam that runs for days and only gets
slow after many hours of running.

On short runs (few hours) my program works fine (processes
dozens of records per second) but after half a day or so
it slows to taking a few seconds per record.  "-r profile"
and set_trace_func are pretty intrusive and I fear my
program that runs for days would take weeks.    Benchmark
has the disadvantage of needing to know what piece of code
to measure; rather than exposing the slow part.

But the biggest advantage in my mind of sampling instantaneous
snapshots of the stack is that it works on any program witout
modification (well, linux's ptrace is most useful if you didn't
strip signals); and it's  almost totally non-intrusive, and does
not skew the timing results at all.