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Very basics things about caching in PHP. Just what it is, how to do, where to cache etc. A little details about APC.
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Caching Basics in PHP
Presented at
The beauty of WebphpXperts seminar 2010
What is Caching?
“A cache is a temporary storage area where frequently accessed data can be stored for rapid access.”
Why do we need it?
● To reduce the number or retrieval queries made to a database
● To reduce the number of requests made to external services
● To reduce the time spent computing data● To reduce filesystem access
A basic example
● A Post
● 23 comments
● Sidebar Contents
● Navigations
● Categories
● Much more...
We have to load -
1. Check if already cached if(the resource is cached) {
Just display it.}
// TOP of your script$cachefile = 'cache/'.basename($_SERVER['SCRIPT_URI']);
// Serve from the cache if existif (file_exists($cachefile)) { include($cachefile); exit;}
2. Generate content and cacheelse{
Get the resource, Display it and Cache.}
ob_start(); // start the output buffer
// – Your normal PHP script and HTML content here –
// BOTTOM of your script
// save the contents of output buffer to the file$fp = fopen($cachefile, 'w');fwrite($fp, ob_get_contents()); fclose($fp);
ob_end_flush(); // Send the output to the browser
3. Expire the cache
● Event/Trigger
● Setting a time
if(new comment || post edited) {Expire cache for this post
}
$cachetime = 120 * 60; // 2 hours
// Serve from the cache if it is younger than $cachetimeif (file_exists($cachefile) && (time() - $cachetime < filemtime($cachefile))) { include($cachefile); Exit; }
So, It was simple. right?
Request
Output
CacheCompute
Miss
Hit
Store
1
2
3
4
Request
Your question is ...
My pages always have an ever changing content and cannot be cached in their entirety
Different Caching Approaches
● Full page caching● Granular page caching● Content pregeneration● Opcode caching● SQL query caching● Browser caching● Object/Variable caching
Everybody is doing it!
● Zend Framework● CakePHP● Kohana● Symfony● ...
● Drupal (modules)
● Wordpress (wpcache)
● Joomla (modules)
● PhpBB● Magento● ...
Frameworks CMSs
What to cache?
Anything that...● you don't want to fetch or compute every time your code runs.● isn't going to change very often
To find them, monitor ● Queries● Page loads● Web Analytics
Where to Cache?
● Local Database faster than Remote Database *● Local Disk faster than Database*● RAM faster than Disk*
* Some conditions apply
APC
● APC: Alternative PHP Cache● Free, Open Source Opcode Cache● Content / Object caching● Simple installation● Stores to local, shared memory● Going to be released as part of PHP6
Installation
Basic PECL (http://pecl.php.net)
pecl install apc
Ubuntu/LinuxMintaptget install php5apc
Windows(http://pecl4win.php.net )
extension=php_apc.dll
A Quick BenchmarkPHP Native PHP w/APC
Concurrency Level 10
Time taken for tests 60 seconds
Complete requests 298 914
Total transferred 643,149 bytes 1,962,675 bytes
HTML transferred 516,971 bytes 1,582,035 bytes
Requests per second 4.91 [#/sec] 15.21 [#/sec]
Time per request 2035.405 [ms] 657.623 [ms]
Time per request(mean, across all concurrent requests)
203.541 [ms] 65.762 [ms]
Transfer rate 10.35 [KB/s] received 31.88 [KB/s] received
How? Opcode caching
Scanning Lexing Parsing Compilation
Object caching
● apc_add() / apc_store() Cache a variable● apc_fetch() Fetch a stored variable from the cache ● apc_delete() Removes a stored variable from the cache
Monitor apc.php
I am...http://ajaxray.com | http://www.facebook.com/ajaxray | http://twitter.com/ajaxray
Anis uddin AhmadCoFounder, WNeeds
http://ajaxray.com | [email protected]
Thank you!
?APC Developers
● George Schlossnagle
● Daniel Cowgill
● Rasmus Lerdorf
● Gopal Vijayaraghavan
● Edin Kadribasic
● Ilia Alshanetsky
● Marcus Börger
● Sara Golemon
