My notes from Aman Gupta's Debugging Ruby webinar by Engine Yard

Debugging Ruby Notes.html

<a href="http://en.wikipedia.org/wiki/Lsof">lsof</a>
----

show open files

lsof -nPp <pid>

<a href="http://linux.die.net/man/1/strace">strace</a>
------

strace -cp <pid> -- summary mode, run it for a while and then hit ^C

OR

strace -ttTp <pid> -o <file> -- system call and arguments as they are happening

ruby 1.8 uses signals to schedule its green threads.  process receives a SIGVTALRM signal every 10ms

in summary mode, you see a lot of calls sigprocmask (ruby bug, shows up in
linux distribution ruby because compiled w/pthread as it is spawning thread to do signaling)


<a href="http://www.tcpdump.org">tcpdump</a>
-------

tcpdump -i eth0 -s <len> -nqA <expr>

tcpdump -w <file> -- dumps to file, and then open file in wireshark for further analysis


<a href="http://code.google.com/p/google-perftools/">PERFTOOLS, google's performance tools</a>
-------------------------------------

download and compile, setup, profile and report

pprof ruby ruby.prof --text or --gif

gem install perftools.rb (only interested in ruby c calls)
 -- real time (wall time) vs. CPU time

perftools does a good job helping you understand a code base as you can see the function call graph

also has object allocation profile

<a href="http://linux.die.net/man/1/ltrace">ltrace</a>
------

ltrace -cp <pid>
ltrace -ttTp <pid> -o <file>

traces library calls as opposed to strace does system calls.

joe domato - new maintainer of ltrace

no good ltrace on os x.  no good strace on mac os x.  dtrace works on mac os x
but doesn't replicate all the functionality of strace and ltrace

<a href="http://www.gnu.org/software/gdb/">gdb</a>
---

gdb <executable>
gdb attach <pid>

1. Attach to a running process
2. Use a coredump

gdb.rb -- gdb with MRI hooks
gem install gdb.rb
gdb.rb <pid> (does not work w/1.9 or OS X) gdb 7 not compatible on OS X

<a href="https://github.com/ice799/memprof">memprof</a> -- a heap visualizer for ruby
-------

gem install memprof

memprof.track

 like bleak_house, but for a given block of code
 use memprof::Middleware in your webapps to run track per request

memprof.dump

 shows you details about objects created during that block.  json output

memprof.dump_all
  
  dump out every single live object as json
  one per line to specified file
  couple hundred mb file

  analyze via
    jsawk/grep
    custom ruby scripts
    mongodb
    ...

memprof.com -- fantastic!!
  
  a web-based heap visualizer and leak analyzer

<a href="https://github.com/bhb/rack-perftools_profiler">rack-perftools</a> -- rack middleware for perftools.rb
--------------

gem install rack-perftools_profiler

middleware that adds urls to app that, if special params are included,
intercepts a request and returns profile info!