memcached FTW!
Because performance does matter
BarCamp Brighton 2 - March 16 2008
Marco van Hylckama Vlieg
marco@i-marco.nl
http://www.i-marco.nl/weblog/

memcached
• memcached is used by very large, high
profile websites such as Livejournal,
Wikipedia and Facebook
• General purpose, scalable caching solution
• Extremely fast
• Extremely easy to use

Universal
• memcached can be used with just about
any programming language
• Runs on almost any box
• Multiple boxes can be deployed
• Can be used with PHP, Python, Perl, Java,
C#, Ruby, ...

How does it work?
• Store anything that can be serialised
• Store with unique key
• Fetch back with this unique key
• Expire time can be set

Usage pattern
• Store items with key and expire time
• Request item :
• found? return it!
• not found? produce item and store in
cache
• If needed, create own expiration
mechanism

Limitations
• Can’t dump contents of the cache
• Cache is not persistent
• Not redundant
• No security
• Max 1MB - 42 bytes cached object size (can
be increased at compile time)

What to cache?
• SQL resultsets
• Whole pages
• XSLT Transformation results
• Generated HTML fragments
• Images (thumbnails)
• Anything ‘expensive’

PHP and memcache
• memcached daemon
• PHP memcache PECL extension (not
installed by default)
• procedural and OO interfaces available

running the daemon
• memcached -d -m 1024 -p 11211

Basic usage
// create Memcache object
$objMem = new Memcache;
// Store something
$objMem->set( $key, $value, $compress, $expire );
// Retrieve something
$retrievedItem = $objMem->get( $key );
// Manual expire / delete
$objMem->delete( $key, [$timeout] );

Memcache singleton
<?php
require_once(\"constants.php\");
class memSingleton extends Memcache {
private function __construct() {}
private function __clone() {}
static private $objMem = NULL;
public static function getMem() {
if (self::$objMem == NULL) {
self::$objMem = new Memcache;
if(!@self::$objMem->connect(__MEMHOST, __MEMPORT)) {
throw new Exception('FAIL! ZOMG! Memcache server not available.');
}
}
return self::$objMem;
}
}
?>

SQL Caching function
function cachedSQL($sSQL, $nExpire) {
try {
if($aResultSet = memSingleton::getMem()->get(MD5($sSQL))) {
echo '<p>CACHE HIT!</p>';
return $aResultSet;
}
}
catch(Exception $e) {}
// manually retrieving uncached item
try {
$objResultSet = PDOSingleton::getInstance()->query($sSQL);
// Store the resultset in the cache
$aResultSet = Array();
foreach($objResultSet as $row) {
$aResultSet[] = $row;
}
if(!@memSingleton::getMem()->set(MD5($sSQL), $aResultSet, true, $nExpire)) {
echo '<p><strong>CAUTION</strong>: CACHE IS DEAD! Serving uncached data.</p>';
return $aResultSet;
}
echo '<p>CACHE MISS!</p>';
return $aResultSet;
}
catch(PDOException $e) {
die(\"TEH DATABASE HAS FAIL. It cried: \" . $e->getMessage());
}
}

STOP!!!
demo time

Resources
• http://www.danga.com/memcached/
• http://www.php.net/memcache
• http://www.i-marco.nl/weblog/