Very basics things about caching in PHP. Just what it is, how to do, where to cache etc. A little details about APC.

1. Caching Basics in PHP
Presented at
The beauty of Web
phpXperts seminar 2010

2. What is Caching?
“A cache is a temporary storage area
where frequently accessed data can be
stored for rapid access.”

3. 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

4. A basic example
●
A Post
● 23 comments
● Sidebar Contents
●
Navigations
● Categories
● Much more...
We have to load -

5. 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 exist
if (file_exists($cachefile)) {
include($cachefile);
exit;
}

6. 2. Generate content and cache
else{
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

7. 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 $cachetime
if (file_exists($cachefile)
&& (time() - $cachetime < filemtime($cachefile))) {
include($cachefile);
Exit;
}

8. So, It was simple. right?
Request
Output
Cache
Compute
Miss
Hit
Store
1
2
3
4
Request

9. Your question is ...
My pages always have an ever changing content
and cannot be cached in their entirety

10. Different Caching Approaches
● Full page caching
● Granular page caching
● Content pre­generation
● Opcode caching
● SQL query caching
● Browser caching
● Object/Variable caching

11. Everybody is doing it!
●
Zend Framework
●
CakePHP
●
Kohana
●
Symfony
●
...
●
Drupal (modules)
●
Wordpress (wp­cache)
●
Joomla (modules)
●
PhpBB
●
Magento
●
...
Frameworks CMSs

12. 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

13. Where to Cache?
●
Local Database faster than Remote Database *
●
Local Disk faster than Database*
●
RAM faster than Disk*
* Some conditions apply

14. 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

15. Installation
Basic PECL (http://pecl.php.net)
pecl install apc
Ubuntu/LinuxMint
apt­get install php5­apc
Windows
(http://pecl4win.php.net )
extension=php_apc.dll

16. A Quick Benchmark
PHP 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

17. How? Opcode caching
Scanning
Lexing
Parsing
Compilation

18. 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

19. Monitor apc.php

20. I am...
http://ajaxray.com | http://www.facebook.com/ajaxray | http://twitter.com/ajaxray
Anis uddin Ahmad
Co­Founder, WNeeds
http://ajaxray.com | anisniit@gmail.com

21. Thank you!
?
APC Developers
● George Schlossnagle
● Daniel Cowgill
● Rasmus Lerdorf
● Gopal Vijayaraghavan
● Edin Kadribasic
● Ilia Alshanetsky
● Marcus Börger
● Sara Golemon