Caching, Memcached And Rails

Caching, Memcached, and Rails Mike Perham http://mikeperham.com Wednesday, March 25, 2009

Me Maintainer of memcache-client, shipped with Rails Hardcore performance nerd Wednesday, March 25, 2009

Performance Let me Tell you a Story... Wednesday, March 25, 2009

Performance Tuning Remove unnecessary Functionality Tune necessary Functionality ONLY THEN, add caching last ALWAYS track before/after timings Wednesday, March 25, 2009

Caching Cache the results of expensive operations Why is this memoization dumb? Wednesday, March 25, 2009

Why Dumb? SCALABILITY! FRESHNESS! Wednesday, March 25, 2009

Rails Built in support for memcached since Rails 2.1 conﬁg/environments/production.rb: Wednesday, March 25, 2009

Request Varnish Apache Rails DB Memcached Standard Toolset for Rails 2.3 Further == Slower Wednesday, March 25, 2009

Caching Mechanisms HTTP Proxy FASTER Page Action Fragment SLOWER Object Wednesday, March 25, 2009

HTTP Proxy HTTP/URL caching with Varnish Expires, Etag, Cache-Control headers 5-10k req/sec! Wednesday, March 25, 2009

Page Caching ERB --> Static HTML Uh oh, uses the ﬁlesystem! Apache = 1-5k req/sec Wednesday, March 25, 2009

Action Caching Runs ﬁlters (e.g. authorization) Can use any cache strategy File, memory, memcached Wednesday, March 25, 2009

Fragment Caching Parts of the page are unique per user Fragment cache the various UI boxes Dynamically assemble HTML from the cache Wednesday, March 25, 2009

Object Caching Built-in AR support for “smart” keys Rails.cache.fetch(post.cache_key) { expensive_calc(post) } “#{table_name}/#{self.id}-#{self.updated_at.to_i}” Support for complex dependencies Wednesday, March 25, 2009

Expiration “There are only two hard things in Computer Science: naming and cache invalidation” Explicit expire_page :controller => ‘users’, :action => ‘index’ expire_action :controller => ‘users’, :action => ‘index’ Rails.cache.delete(‘key’) Observers Wednesday, March 25, 2009

Expiration (Cont’d) Time-based Rails.cache.fetch(‘key’, :expires_in => 1.hour) { ... } expires_in(2.hours) # sets page’s HTTP max-age attribute Versioning Rails.cache.fetch(user.cache_key) { ... } Wednesday, March 25, 2009

Memcached Giant Hash of Fixed Size Time-based expiration LRU eviction Operations: GET, SET, APPEND, INCR, CAS Limited to 1MB per value, 250 chars per key Wednesday, March 25, 2009

Facebook 100s of servers w/ 28TB of RAM 5 billion page views/day 400k req/sec from memcached Wednesday, March 25, 2009

Performance Wednesday, March 25, 2009

Mongrel + Nginx Varnish Nginx WEB1 M1 M2 M1 M2 Memcached Memcached APP1 APP2 Wednesday, March 25, 2009

Apache + Passenger Varnish HAProxy WEB1 Memcached Memcached Apache Apache Rails Rails Rails Rails APP1 APP2 Wednesday, March 25, 2009

Advanced Spread your cache across a farm of memcached Use the memcaches_page plugin Use AJAX for user-speciﬁc widgets Wednesday, March 25, 2009

Advice Cache late in the development cycle, after tuning! Memcached gives you time-based expiration, versioning and multi-machine support. Cache as early in the request as possible! Varnish Apache Rails DB Wednesday, March 25, 2009

THANK YOU! HTTP://MIKEPERHAM.COM MPERHAM@GMAIL.COM QUESTIONS? Wednesday, March 25, 2009

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Caching, Memcached And Rails

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