Rails performance: Ruby GC tweaking
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The document discusses optimizing Ruby on Rails performance by tweaking the garbage collector settings. It begins by explaining the default GC settings and how they are not optimal for high traffic Rails applications. It then provides examples of settings used by GitHub that increase memory allocation and decrease frequency of garbage collection to reduce response times. Benchmark results show memory usage increase but response times decrease after applying the optimizations. The conclusion advocates measuring performance, optimizing bottlenecks, and using REE or Ruby 1.9 in production.
Rails performance: Ruby GC tweaking
- 1. Rails performance: Ruby GC tweaking #ParisRB Vlad ZLOTEANU August 2, 2001 @vladzloteanu Software engineer @ Dimelo Copyright Dimelo SA www.dimelo.com
- 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 www.dimelo.com
- 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/s Copyright Dimelo SA www.dimelo.com
- 4. Problem Medium response time ~ 400 ms WTF?? Copyright Dimelo SA www.dimelo.com
- 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 UnionStation Copyright Dimelo SA www.dimelo.com
- 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 leaks Copyright Dimelo SA www.dimelo.com
- 7. Memory / GC issues - How do I know it’s a memory/GC issue? - Server logs - Profilers (memprof) - Monitorization services (newrelic) Copyright Dimelo SA www.dimelo.com
- 8. Ruby Garbage Collector - Conservative - Stop-the-world - Mark-and-sweep process Copyright Dimelo SA www.dimelo.com
- 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 sized Copyright Dimelo SA www.dimelo.com
- 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 ones Copyright Dimelo SA www.dimelo.com
- 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 www.dimelo.com
- 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 www.dimelo.com
- 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 2256 Copyright Dimelo SA www.dimelo.com
- 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 www.dimelo.com
- 15. Thank you! • Questions? Copyright Dimelo SA www.dimelo.com