Cache Money
Practical Application
Wolfram Arnold
www.rubyfocus.biz

Outline
Caching in Rails
●
Model caching
●
Cache Money API
●
What's not covered?
●
How do I know it's cached?
●
Advice—best bang for the buck?
●
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:cache => Rails
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Page Caching
class CorpController < ApplicationController
caches_pages :about, :privacy, :tos
end
Bypasses application
●
Fast!
●
Static content only—rare
●
Requires local file system
●
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:choose => Store
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Backends
config.cache_store =
:mem_cache_store
:memory_store
:file_store, \"/path/to/cache/directory\"
:drb_store, \"druby://localhost:9192\"
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Action Caching
class UsersController < ApplicationController
caches_action :show
def update
expires_action
end
end
Can run before filters
●
~1 order of magnitude slower
●
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Fragment Caching
<% cache do %>
Some complicated slow-to-render
content here...
<% end %>
Stores of rendered snippets keyed on action
●
Maintaining expiration code tricky
●
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:sweep => Cache
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Sweeping
class ListSweeper < ActionController::Caching::Sweeper
observe List
def after_save(record)
expire_page(:controller => \"lists\",
:action => %w( show public feed ), :id => list.id)
expire_action(:controller => \"lists\", :action => \"all\")
# every place where List instances are used
end
class ListsController < ApplicationController
caches_action :index, :show, :public, :feed
cache_sweeper :list_sweeper, :only => [ :edit, :destroy ]
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end

:cache => Query
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Query Cache
User Load (0.1ms) SELECT * FROM `users`
WHERE (`users`.`id` = 1572302630)
CACHE (0.0ms) SELECT * FROM `users`
WHERE (`users`.`id` = 1572302630)
Exact same query
●
No updates in between
●
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:cache => Models
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Models
Controllers
Views
memcached
DB
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:cache => MONEY
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User.find(id)
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Models
memcached
DB
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Cache Money
User.find(id)
alias_method_chain :find_every, :cache
alias_method_chain :find_from_ids, :cache
alias_method_chain :calculate, :cache
User.get(“User:1/#{id}”)
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Indexed
class User < ActiveRecord::Base
index :name, :order => :desc
end
User.all(:conditions => ['id = ?', ...])
User.find_by_name(:order => “DESC”)
User.all(:conditions => ['name = ?, ...],
:order => “DESC”)
User.count
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User.count(:name => “Jones”)

:expiry => how?
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Expiry
after_create :add_to_caches
after_update :update_caches
after_destroy :remove_from_caches
User.create
@user.attributes = { :name => ... }
@user.destroy
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:what => else?
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Associations
class User class Video
has_many :videos index [id, user_id]
end belongs_to :user
end
@user.videos.find(id)
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:must_have => Joins
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Joins :through
class Video
has_many :taggings
has_many :tags, :through => :taggings
end
@video.tags
SELECT `tags`.* FROM `tags`
INNER JOIN taggings ON tags.id = taggings.tag_id
WHERE ((`taggings`.taggable_id = 1912438135) AND
(`taggings`.taggable_type = 'Video'))
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:include => Trouble
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Joins :include
Video.find(:all, :include => :taggings,
:conditions => “taggings.id IS NOT NULL”)
SELECT `videos`.`id` AS t0_r0, `videos`.`user_id` AS
t0_r1, `taggings`.`id` AS t1_r0,
`taggings`.`tag_id` AS t1_r1,
`taggings`.`taggable_id` AS t1_r2,
`taggings`.`taggable_type` AS t1_r3 FROM `videos`
LEFT OUTER JOIN `taggings` ON
`taggings`.taggable_id = `videos`.id AND
`taggings`.taggable_type = 'Video' WHERE
(taggings.id IS NOT NULL)
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class Video
has_many :taggings
end
Video.find(:all, :include => :taggings)
→ 1 SQL Query, not cacheable
Video.find(:all).each do |v|
v.taggings
end
→ N + 1 SQL Queries, cacheable
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:options_for => Joins
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Options for join queries
Denormalize
●
Use after_save, after_destroy to keep in sync
–
Maintain your own index
●
e.g. acts_as_most_popular
–
Deconstruct into multiple queries
●
e.g. drop :include
–
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:caching => Evolution
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If it's supposed to help if must taste bitter.
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Even if tastes bitter, it might still not help.
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Thank You!
github.com/nkallen/cache-money/
github.com/wolframarnold/acts_as_most_popular
Wolfram Arnold
www.rubyfocus.biz
wolfram@rubyfocus.biz