A PHP Acelerator is a tool that will enhance the performance of web applications written for the PHP scripting language. The free Alternative PHP Cache (APC) is distributed as a PEAR package.
If you run your own LAMP server with PHP applications, then please install it. The Moodle documentation includes information on setting up APC; including testing before and after performance with "Apache Bench"
Installation
Assuming you already have Apache2 and PHP5 (with dev extensions so PECL can run phpize), it's as easy as
# make sure we have the development headers and apxs2 binary for threaded versions of apache2
sudo apt-get install apache2-threaded-dev
# install the APC extension
sudo pecl install APC
# pecl would have updated my php.ini file automatically, but it did not know where to look.
# set it for future reference
sudo pear config-set php_ini /etc/php5/apache2/php.ini
# do the configuration of php settings file myself
sudo vi /etc/php5/apache2/php.ini
# test and restart apache
sudo apache2ctl configtest
sudo apache2ctl graceful
# make a symbolic link to the system front-end
cd /var/www
sudo ln -s /usr/share/php/apc.php
MediaWiki
MediaWiki can take advantage of the APC cache if you tell it to. see The Manual for cache settings, and set mw:Manual:$wgMainCacheType in LocalSettings.php:
$wgMainCacheType = CACHE_ACCEL;
Troubleshooting
If you notice sluggishness in your site after installing APC, then check out the front-end (apc.php). The sure sign that you need to increase your cache size is that the "cache full" count is greater than one.
- Check your memory
- Increase the Shared Memory Size for APC in your php.ini file e.g.
apc.shm_size = 128 - Restart Apache
- Use the Apache Bench tool to test performance with and without APC enabled.
Notes
APC, aside from speeding up your website, also provides a storage mechanism outside the traditional cookie/session mechanism. So, you could set an application variable or constant and (assuming that the cache is not cleared, etc.) retrieve that value from another context.