Caching your rails application
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Rails Need short bursts of speed?
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Bernard from Openminds talks about caching your Rails appication.
Transcript of Caching your rails application
RailsNeed short bursts of speed?
I’m a thief
• http://railslab.newrelic.com/
Perception
Communication: Two parts
• Server speed
• Browser speed
Browser speed
• Firebug / Safari developer
• YSlow
• Different parts of a site
Webpage parts
• Page itself (<html> ... )
• Additional files (CSS, JavaScript)
• Images
• ... generating dynamic content
Siteparts
• 10 requests:10 times slower as one request
• stylesheet_tag :defaults, ‘screen’, :cache => ‘all’
images
• asset hosts
• Content Delivery Network
Page Caching
Why?
• Code parsing: 20 to 50 req/second
• Webserver: easily > 100 req/sec
• Webserver stresses less, less database queries
• Why not, it is easy (with rails)...
implementation
result
expire_page
expires-result
conclusion: page cache
• very simple
• limited scope to apply
• cache invalidation! Important!
Cache Expiry
Why not expire_page in the action?
• Not DRY (update, create, destroy,...)
• after_filter possible, but other controllers might need to expire the cache
after_filter• PostsController (clear_posts_cache)
• CommentsController (clear_posts_cache)
sweeper
• observer on controller and model
• if saved, call clear_posts_cache
• if deleted, call clear_posts_cache
how
Page caching - part 2
• Ajax Callbacks for dynamic data
login/logout
• pain!
Action Caching
Action cache
• Cached output stored
• Filters are processed before the cached version is returned to the browser
• Example: authenticatie
caches_action
action cache
• Filter is executed before sending the reply
• Output is the same for everyone!
Welcome <username>
• content is cached
• layout is rendered
Warning! Attention!
• fetch needed data with a before_filter
• action is not executed!
Conditional AC
• caching only on certain conditions
Action Caching
• when?
• execute code on each hit (authentication)
• result remains the same
• very easy to implement
Fragment Caching
Fragment caching
• Cache part of a page
• Logical blocks are candidates
Example
Fragment Caching
No useless actions
Fragment Cache expiry
• expire_fragment
PC/AC Storage
Page cache storage
• on disk
Storage: action / fragment cache
• memory (default) or syncronised memory
• file on disk
• drb
• memcache (normal or compressed)
• custom_store (not hard to impelement!)
DYI
DYI caching
• Caching hard parts in the code
• Only spend cycles when really needed
Client-side caching
• The cloud is there, use it
Three tags
• max-age
• etag
• last_modified
max-age
etag
• rails has this embedded
• MD5(body) => etag
• 304 Not Modified
etag
• Beware, the complete parsing is done!
• Less bandwidth / traffic
• Client load time faster
etag
last_modified
Scary technology?
• memcached
• reverse proxy’s
Memcached
• Daemon
• Is a big hash in memory
• Rails has default routines for this
• Hoster / setup should support this
Reverse Proxy’s
• a proxy, but on the server side
• controle over expiry: max_age + etag
• expiry remains a pain
Rack::Cache
• gem install rack-cache
• rails 2.3 needed!
Need for speed?
• Database (n+1, joins / includes)
• Disk IO
• Implementing caching
• Browser caching
• External components (CDN, memcached, ...)
