MemcachedTalk

8/14/2019 MemcachedTalk

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MemcacheRob [email protected]

Lead DeveloperThe Sound Alliance
mailto:[email protected]:[email protected]


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About Memcached

conceived by Brad Fitzpatrick as asolution to the scaling issues faced

by Livejournalmemcached is a high-

performance, distributed memoryobject caching system, generic innature, but intended for use inspeeding up dynamic webapplications by alleviating

database load


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Who we are

Inthemix.com.au

Australias busiest music website~ 250,000 pages per dayPlus two other busy sites!Maximum performance for the

hardware we have


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Current

Architechture3 Linux servers

ApacheLighttpd

Memcache1 MySQL Master


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Why do we use

memcached?CMS written in OO style, usingActiverecord

PHP4 and objects don't mix toowellActiverecord gave us fast

development but reducedperformance

Call us greedy, but we want both

Use Rails Memcache!


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Our Application

CMS written from the ground upEffectively three sites running on

one codebase

Uses three seperate databases,but aiming to consolidate more

Has data namespacingimplemented in most places

But seperation is not quite there

yet!


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Our Memcache

Setup

We have 3 webservers runningmemcache

Each server runs three daemonson separate ports - one for eachsite (more on this later!)


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Memcache PoolEach daemon knows about theother 2 daemons and connects to

them over TCP

This allows us to store data once,and access it from any server,whether in the pool or not

Hashing algorithm means that agiven key maps to a single serverEfficient use of memory

Efficient for cache clearing


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Memcache PoolBut what if we lose a server? WecanIgnore it - we simply get misses

for any keys we attempt toretrieve

Remove it - our hashingalgorithm breaks... :(

We can also add new servers tothe pool after data has been

stored, but the same hashing


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Memcache Pool

Consistent hashing will solve theproblem of removing or adding

servers once data has beenhashed

Currently in its infancy - not reallyproduction ready

We simply monitor our daemonsand restart if required


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Installing

Memcached

packaged for Fedora, RHEL4/5,

Ubuntu, Debian, Gentoo and BSD

OSX? Use Ports!sudo port install memcache

sudo gem install memcache-client

sudo gem install cached_model


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Memcache and

Ruby

Well use the memcache-clientgemPure Ruby implementation

Pretty fast!


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Storing Stuff

Cache.set 'favourite_artist', 'Salvador Dali'skateboarder =Cache.get 'favourite_artist'

Cache.delete 'favourite_artist'


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Memcache

NamespacesMemcache doesnt havenamespaces, so we have toimprovise

Prefix your keys with a namespaceby setting the namespace whenyou connect

Our solution:Run multiple memcacheinstances on different ports

Makes it easier to clear out


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Roll your own?

Memcache-client provides basiccache methodsWhat if we extended ActiveRecord?

We can, with active_model


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Storing Stuff Part

Deuxrsharp$ sudo gem install cached_model

require'cached_model'

memcache_options = { :compression => true, :debug => false, :namespace => 'hifibuys', :readonly => false, :urlencode => false

}

CACHE =MemCache.new memcache_optionsCACHE.servers ='localhost:11211'


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Storing Stuff Part

Deux

classArtist < CachedModel

end


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cached_model

PerformanceCachedModel is not magic.CachedModel only accelerates simple

finds for single rows.

CachedModel wont cache every queryyou run.

CachedModel isnt smart enough todetermine the dependencies betweenyour queries so that it can acceleratemore complicated queries. If you want to

cache more complicated queries you
http://dev.robotcoop.com/Libraries/cached_model/classes/CachedModel.htmlhttp://dev.robotcoop.com/Libraries/cached_model/classes/CachedModel.htmlhttp://dev.robotcoop.com/Libraries/cached_model/classes/CachedModel.htmlhttp://dev.robotcoop.com/Libraries/cached_model/classes/CachedModel.htmlhttp://dev.robotcoop.com/Libraries/cached_model/classes/CachedModel.htmlhttp://dev.robotcoop.com/Libraries/cached_model/classes/CachedModel.htmlhttp://dev.robotcoop.com/Libraries/cached_model/classes/CachedModel.htmlhttp://dev.robotcoop.com/Libraries/cached_model/classes/CachedModel.htmlhttp://dev.robotcoop.com/Libraries/cached_model/classes/CachedModel.html


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Other options

acts_as_cached provides a similarsolution


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Memcache Storage

Memcache stores blobs

The memcache client handlesmarshalling, so you can easilycache objects

This does however mean that theobjects arent necessarily cross-language


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Memcache Storage

The most obvious things to storeare objects

We cache articlesWe cache collections of articles

We cache template dataWe cache fragments

We dont cache SQL queries


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What we cache

Our sites are fairly big and data-rich communities

Almost every page has editoriallycontrolled attributes along with

user generated contentLike...


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Our Example

DatasetArticle

Joins Artists

Joins LocationsJoins Genres

Joins Related ContentJoins Related Forum Activity

Joins Related Gallery Data


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Our Example

DatasetArticle (continues)

...

Joins Media Content

Joins CommentsJoins Rollcalls

Joins other secret developments


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Our ExampleAn article requires many datafacetsMost dont change that oftenWe also know when they changeYay for the Observer pattern

User content changes muchmore regularlyCan be changed from outside

our controlled area (e.g.

ur xamp e


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ur xamp eSummarySummaryData can be loosely divided into

editorially controlled and user-

generatedCache editorially controlled

content separately from user-

generated contentSimplest way to implement is in

fragment caching


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Fragment CachingMemcache allows timed expiry of

fragments

Identify areas that changeinfrequently and cacheRemember to measure

performance before and afterEvidence suggests very large

gains!

Use memcache_fragments


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Caching Fragments

rsharp$ sudo gem install memcache_fragments

require'memcache_fragments'

memcache_options = { :compression => true, :debug => false, :namespace => 'hifibuys', :readonly => false, :urlencode => false

}

CACHE =MemCache.new memcache_optionsCACHE.servers ='localhost:11211'


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Caching Fragments

ActionController::Base.fragment_cache_store =:mem_cache_store ,{}ActionController::Base.fragment_cache_store.data = CACHE, {}ActionController::CgiRequest::DEFAULT_SESSION_OPTIONS.merge!({ 'cache'=> CACHE })


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Caching Fragments

cache/key', :expire => 10.minutes do %> .


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Memcache

SessionsWe could store our session inMemcacheGreat for load balancing - share

across a server farm withoutusing a DB store

Ideal for transient data

Solution exists indb_memcache_store

DB backend with memcachelayer - the best of both worlds


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In Summary

Memcache gives you a distributedcache store

Very fast and very easy to use

Lots of ruby and rails librariesmemcache_client

cached_model

db_memcache_storememcache_fragments


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Any Questions?

Documents

MemcachedTalk