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Rails performance: Ruby GC tweaking


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  • 1. Rails performance: Ruby GC tweaking #ParisRB Vlad ZLOTEANU August 2, 2001 @vladzloteanu Software engineer @ DimeloCopyright Dimelo SA
  • 2. What we develop Frontend products -Collaborative platforms, ‘forum-like’, white-labeled, for big accounts (a kind of GetSatisfaction / UserVoice, but.. Better ;) ) Backend product -SocialAPIs client -(a kind of TweetDeck, but for multiple channels, and designed for teams/multiple users per account)Copyright Dimelo SA
  • 3. Stats on Dynamic requests - on HTML/XHTML dynamic requests (we don’t count CSS, JS, images, etc) 20 req/s Web Peaks of 40 req/s 10 req/s APIs Peaks of 25 req/sCopyright Dimelo SA
  • 4. Problem Medium response time ~ 400 ms WTF??Copyright Dimelo SA
  • 5. Ruby perf toolbox Benchmark Server logs Apache Benchmark (ab, ab2) Profile Rack::Bug RailsBench RubyProf RBTrace Memprof Scrap BleakHouse .. Valgrind ltrace Std surveillance Cacti Nagios Surveilance & profiling NewRelic RPM UnionStationCopyright Dimelo SA
  • 6. Finding the problem(s) - DB queries (unoptimized queries, n+1) - External services (EG external RSS feeds) - Lots of partials, low or inexistent cache - Slow session storage - Memory issues - Unoptimized GC - Memory leaksCopyright Dimelo SA
  • 7. Memory / GC issues - How do I know it’s a memory/GC issue? - Server logs - Profilers (memprof) - Monitorization services (newrelic)Copyright Dimelo SA
  • 8. Ruby Garbage Collector - Conservative - Stop-the-world - Mark-and-sweep processCopyright Dimelo SA
  • 9. Ruby default GC settings RUBY_HEAP_MIN_SLOTS=10000 -Initial number of heap slots. It also represents the minimum number of slots, at all times -a new rails app boots up with almost 500k objects on the heap(mostly nodes) RUBY_HEAP_SLOTS_INCREMENT=10000 -The number of new slots to allocate when all initial slots are used RUBY_HEAP_SLOTS_GROWTH_FACTOR=1.8 -Next time Ruby needs new heap slots it will use a multiplicator -New stab is almost double sizedCopyright Dimelo SA
  • 10. Ruby default GC settings (2) RUBY_GC_MALLOC_LIMIT=8000000 -force GC after 8 MB malloc/realloc -High traffic Rails servers can easily allocate more than 8 MB per request RUBY_HEAP_FREE_MIN=4096 -The number of free slots that should be present after GC finishes running. If there are fewer slots than those defined it will allocate new onesCopyright Dimelo SA
  • 11. Find your numbers - Start with enough memory to hold Rails (Ruby’s default is practically nothing) - Increase it linearly if you need more (Ruby’s default is exponential increase) - Only garbage-collect every XX million malloc calls (Ruby’s default is way too small) - Benchmark, benchmark, benchmark..Copyright Dimelo SA
  • 12. GitHub numbers • RUBY_HEAP_MIN_SLOTS=800000 (10000) • RUBY_HEAP_FREE_MIN=100000 (4096) • RUBY_HEAP_SLOTS_INCREMENT=300000(100 00) • RUBY_HEAP_SLOTS_GROWTH_FACTOR=1(1.8) • RUBY_GC_MALLOC_LIMIT=79000000(8000000 )Copyright Dimelo SA
  • 13. Demo (using ApacheBench) - Frontend app, 15 requests, concurrency 1 Before optimisations: Memory usage: 130 MB Execution time(ms): 228 344 322.0 316 4797 After optimisations: Memory usage: 160 MB Execution time(ms): 120 181 190.0 150 2256Copyright Dimelo SA
  • 14. Conclusions - use REE on prod (or Ruby 1.9) - measure, measure, measure (don’t forget to GC.enable_stats) - optimise what matters - And yes, 5 lines of code can make a difference ;)Copyright Dimelo SA
  • 15. Thank you! • Questions?Copyright Dimelo SA