Scaling web applications using Memcache

Sudar Muthu (@sudarmuthu)http://sudarmuthu.com

Research EngineerYahoo ResearchChennai Geeks - Meetup20-Nov-2010

AgendaOverviewMemcache is notHow Memcache worksGeneral UsageMemcache LimitsClient LibrariesCommon Use casesTips for optimizationUsing Memcache in WordPress

OverviewA high-performance Distributed

Memory Object Caching SystemIntended for speeding up

dynamic web applications by alleviating database load.

Open source & distributed under a “permissive free software license”.

Uses RAM for storage Acts as a dictionary of stored

data with key /value pairs

Memcache is not..It is not a databaseIt does not provide redundancyIt doesn't handle failoverIt does not provide

authenticationIt does not allow locksNo direct dump or backup

possible

How Memcache worksTwo stage hash, like a giant hash

table looking up key=value pairsClient hashes the key against a

list of servers When the server is identified, the

client sends its request Server performs a hash key

lookup for the actual data

General UsageFirst look up in memcache before

querying the database.If present, return it.Else query the database, store it

in memcache and return it.If the data changes, delete it

from cache.

Memcache LimitsA single value cannot contain

more than 1 MB of data.A single key cannot be more than

250 characters in length.Normally a single memcache

instance cannot be more than 2 GB in size.

Client LibrariesPerl, Python, Ruby, Java, C#, CPostgreSQL (access memcached

from procs and triggers)MySQL (adds memcache_engine

storage engine)PHP (pecl/memcache)

Client Libraries – PHP API

Key Methods bool Memcache::connect ( string $host [,

int $port [, int $timeout ]] ) bool Memcache::set( string $key , mixed

$var [, int $flag [, int $expire ]] ) string Memcache::get ( string $key [, int

&$flags ] ) bool Memcache::delete ( string $key [, int

$timeout ] )

More: http://www.php.net/memcache

Common Use cases - 1Simple query result caching

$key = ”some:unique:key”;$value = $memcache‐>get($key);if ($value) {    

return $value;  }  else {    

// Run the query get the result data$result = $db‐>query(“query”);      $memcache‐>set($key, $result, TRUE, 300); 

// Store the result of the query for 5 minutes      return $result; 

} 

Common Use cases - 2 Caching network/webservice calls

$key = ”some:unique:key"; $value = $memcache->get($key);if ($value) { return $value; } else {

// Download the page $url = ”Your webservice url";

$result = fetch($url); $memcache->set($key, $result, false, 86400); // Store the result of the query for a day return $result;

}

Common Use cases - 3Throttle user activity

$key = “some:unique:key”; if ($memcache->get($key)) { //Deny access

return false; } else {

$memcache->set($key, “1”, false, 60); //Allow access return true;

}

Tips for OptimizationPre warm your cache using scripts Batch your requests using multi-get

◦values= get(Array(“Foo”,”Bar”,”Baz”))Cache things other than SQL data!

◦XML, HTML, Page fragmentsReplicate data across clusters

◦Do set/delete in multiple clusters  ◦Read from either cluster

Run multiple instances on the same serverIf you know the data, implement a simple

encoding scheme

Using Memcache in WordPressDownload Memcached Object

Cache Plugin from http://wordpress.org/extend/plugins/memcached/

Set up memcached serversInstall pecl memcache extentionCopy object-cache.php to wp-

content directory (not the Pluing’s directory)

You are done

Questions?

Thank you