Alternative PHP Cache (APC) - Installation guide.

Referred web sites:

• http://www.php.net/manual/en/book.apc.php
• http://php.find-info.ru/php/016/ch20lev1sec1.html
• http://linuxaria.com/howto/everything-you-need-to-know-about-apc-alternate-php-cache?lang=en
• http://lampzone.wordpress.com/2010/03/26/how-does-apc-work/

What is APC ?

• APC is stands for Alternative PHP Cache
• APC is a free and open opcode cache for PHP
• Its goal is to provide a free, open, and robust framework for caching and optimizing PHP intermediate code.

Who need APC ?

• System Administrator who need increase the performance of a PHP web site.
• Web designers/developers or programmers who develop web applications using Yii,WordPress,Drupal or any framework.

How can I find more information about APC ?

• You can read about apc on http://www.php.net/manual/en/book.apc.php

How APC works ?

• Information collected from linuxaria.com  and lampzone.wordpress.com

• First of all, You need to know how a PHP application run by the Zend Engine (Opcodes and Op Arrays)

1. The first step is reading the PHP code from the filesystem and put it into memory.
2. Lexing : The php code inside is converted into tokens or Lexicons.
3. Parsing : During this stage, tokens are processed to derive at meaningful expressions.
4. Compiling : The derived expressions are compiled into opcodes.
5. Executing : Opcodes are executed to get the final result.

• The goal of APC is bypass the steps from 1 to 4, caching in a shared memory segment the opcodes generated and then copies them into The execution process so Zend can actually execute the opcodes.

How to install APC ?

• There are 2 ways to install APC
1. Install APC is with PECL
• With this method you’ll download the last source and compile it for you computer.
• For Debian and Ubuntu

sudo apt-get install php-pear php5-dev apache2-threaded-dev build-essential

sudo pecl install apc

2. Install APC from a repository of your distribution.
• On Debian and Ubuntu APC is available on the main repository with this name:

sudo apt-cache search apc php
php-apc - APC (Alternative PHP Cache) module for PHP 5

sudo aptitude install php-apc

• On Red Hat Enterprise, Centos or Fedora you can use this command:

sudo yum install php-pecl-apc

APC configurations

• Once installed APC must be enabled in the configuration file of PHP: php.ini, if you have installed APC from a package this is already done and you just have to restart Apache (or FastCGI daemon like FPM) to see a new APC section in phpinfo() which will confirm it’s enabled.
• Otherwise you have to include in your php.ini this line:

extension=apc.so

How to set APC runtime configuration ?

• Visit : php.net