Debugging and Profiling Rails App

Overview of Debugging and Profiling tools for Rails

1. Debugging and Profiling Rails App David Paluy January 2013
3. Ruby is eating RAM
4. Agenda • “Winter is coming!” • Garbage Collector • Debug Tools • Profiling Tools
5. The Task: Send ~30,000 e-mails
6. Result Before
7. How Ruby Works? Physical RAM Process Heap Ruby Heap Ruby Heap Ruby Object Ruby Object Ruby Object Ruby Object Ruby Object Ruby Object
8. New Object allocation Free List A L L O C A T E D F R E E
9. New Object allocation Free List A L L O C A T E D
10. New Object allocation Free List is empty A L L O C A T E D
11. New Object allocation Free List is empty – Call GC A L L O C A T E D
12. GC Process • GC finds non-reachable objects and adds them to Free List • If Free List is still empty, another Heap allocated
13. MRI GC • “Conservative”: any bit pattern could be a pointer (may produce false positive) • “Stop the world”: no other Ruby code can execute during GC • “Mark & Sweep”: mark all objects in use, than sweep away unmarked objects
14. More Objects => Longer GC => Slow
15. In our case – Out of Memory!
16. How to Debug? • gem "pry-debugger" https://github.com/nixme/pry-debugger • gem "debugger-pry" https://github.com/pry/debugger-pry
17. Tools • ObjectSpace.count_objects • GC debug - Enable heap dump support • gdb.rb (only Linux) Note: memprof works only with Ruby 1.8
18. ObjectSpace.count_objects
19. Enable heap dump support to Ruby Install custom patched version of ruby Usage:
20. https://github.com/tmm1/gdb.rb Attached to existing process and examine the HEAP
21. Result After
22. Profiling Tools • Ruby Benchmark • ruby-prof • perftools.rb (Google perftools for Ruby)
23. Benchmark • gem 'benchmark_suite' https://github.com/evanphx/benchmark_suite
24. ruby-prof gem 'ruby-prof' https://github.com/rdp/ruby-prof
25. ruby-prof Measurements • process time (RubyProf::PROCESS_TIME) • wall time (RubyProf::WALL_TIME) • cpu time (RubyProf::CPU_TIME) • object allocations (RubyProf::ALLOCATIONS) • memory usage (RubyProf::MEMORY) • garbage collections runs (RubyProf::GC_RUNS) • garbage collection time (RubyProf::GC_TIME)
26. perftools.rb https://github.com/tmm1/perftools.rb gem 'rack-perftools_profiler', :require => 'rack/perftools_profiler'
27. rack-perftools_profiler usage
28. KCacheGrind
29. Summary • More Objects => Longer GC => Slow • Examine your HEAP • Use Tools
30. Q&A http://dpaluy.github.com @dpaluy dpaluy@gmail.com http://www.linkedin.com/in/davidpaluy