Debugging and Profiling Rails AppDavid Paluy January 2013

Ruby is eating RAM

Agenda

Winter is coming! Garbage Collector Debug Tools Profiling Tools

The Task: Send ~30,000 e-mails

Result Before

How Ruby Works?Physical RAM

Process Heap

Ruby HeapRuby Object Ruby Object Ruby Object Ruby Object Ruby Object Ruby Object

Ruby Heap

New Object allocationFree ListA L L O C A T E D

F R E E

New Object allocationFree ListA L L O C A T E D

New Object allocationFree List is emptyA L L O C A T E D

New Object allocationFree List is empty Call GCA L L O C A T E D

GC Process

GC finds non-reachable objects and adds them to Free List If Free List is still empty, another Heap allocated

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

More Objects => Longer GC => Slow

In our case Out of Memory!

How to Debug?

gem "pry-debugger" https://github.com/nixme/pry-debugger gem "debugger-pry" https://github.com/pry/debugger-pry

Tools

ObjectSpace.count_objects GC debug - Enable heap dump support gdb.rb (only Linux) Note: memprof works only with Ruby 1.8

ObjectSpace.count_objects

Enable heap dump support to RubyInstall custom patched version of ruby

Usage:

https://github.com/tmm1/gdb.rbAttached to existing process and examine the HEAP

Result After

Profiling Tools

Ruby Benchmark ruby-prof perftools.rb (Google perftools for Ruby)

Benchmark

gem 'benchmark_suite'https://github.com/evanphx/benchmark_suite

ruby-profgem 'ruby-prof' https://github.com/rdp/ruby-prof

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)

perftools.rb https://github.com/tmm1/perftools.rbgem 'rack-perftools_profiler', :require => 'rack/perftools_profiler'

rack-perftools_profiler usage

KCacheGrind

Summary

More Objects => Longer GC => Slow Examine your HEAP Use Tools

Q&Ahttp://dpaluy.github.com @dpaluy dpaluy@gmail.com http://www.linkedin.com/in/davidpaluy