Manual:Cache

MediaWiki is a very complex web-application, this means that it can take some time to render pages. To mitigate these costs, many MediaWiki administrators install one of many caching solutions. They are by no means compulsory, though they can decrease the time it takes pages to load, and decrease server workload. This page is divided into four sections, in order to cache everything, you need to enable a solution from each group. It is very likely that you do not need to cache everything, simply enable things that you can, until you have acceptable performance. In some cases, over-caching will cause a degradation of performance.

Short version: we recommend you use APC and memcached; for interest, this is currently what the Wikimedia Foundation uses for Wikipedia et al. See "How to make MediaWiki fast" and "MediaWiki performance tuning".

PHP caching
PHP works by compiling a PHP file into bytecode and then executing that bytecode. The process of compiling the file into bytecode takes some time. PHP accelerators work by storing the compiled bytecode and executing it directly reducing the time spent compiling code. Examples of PHP accelerators include:


 * APC (Alternative PHP cache). This is available as a package from many Linux distributions (eg Ubuntu 10.04), or from PECL, and is recommended.
 * PHP accelerator
 * eAccelerator - Note: Any version of eAccelerator will work for PHP caching but if you also want to use it for Object caching as well, you need version 0.9.5 (later versions are not compatible). Note: Support for eAccelerator has been removed in MediaWiki 1.19
 * XCache - Note: After Debian installion with apt-get install php5-xcache set xcache.var_size to be >0M (e.g. 16M). Otherwise it may lead to an error.

MediaWiki does not need to be configured to do PHP caching and will "just work" if you install any of them. You can use phpinfo to verify that the cache is installed and configured properly. More information is available from these projects, or Google this information.

Object caching
When MediaWiki assembles a page to show to a user, it performs database queries to gather lots of different pieces of data and then combines it all into the page. Object caching allows MediaWiki to store these combined objects for later retrieval reducing the time spent communicating with the database and assembling pages. This is arguably the most important cache for most installations. MediaWiki can store the cached objects in a number of different places including on a file system, in the database, or in an external caching system like memcached, APC, eAccelerator, or XCache.

Since MediaWiki 1.18.0, you can define your own caching system using $wgObjectCaches.


 * On a single server
 * If you have a PHP byte-code cache, see PHP caching above, you can easily use this to store all of the extra data. This is strongly recommended, and requires the following line in LocalSettings.php:
 * If you are unable to use such a cache, then you may be able to use memcached, see that page for details. This is considerably more complicated, but still very effective.
 * The other two types of object cache use a database for caching. This may (or may not) be better than nothing, but one of the previous two solutions should be tried first.
 * The other two types of object cache use a database for caching. This may (or may not) be better than nothing, but one of the previous two solutions should be tried first.


 * On multiple servers
 * If you have multiple application servers running MediaWiki in a load-balancing configuration, you need to use memcached, detailed instructions are on that page.

If you set $wgMainCacheType then the values for $wgParserCacheType and $wgMessageCacheType will inherit it. You do not need to set those variables unless you plan on doing something very advanced.


 * Disabling caching

Localization caching

 * New in 1.16

After finding out that a large number of the cached objects above were interface messages, the bits of text that are not content, an advanced localisation cache was introduced. Set $wgCacheDirectory in LocalSettings.php to a valid path to use.

Page caching
Once the entire page has been rendered, it is often served multiple times, identically, to not-logged-in users. There is no need to ask MediaWiki to repeat itself.


 * On multiple servers
 * If you have multiple application servers running MediaWiki in a load-balanced configuration, use an existing HTTP-level cache, such as varnish or squid.


 * On a single server
 * You may use varnish/squid, as above, or leverage any support your web-server has for HTTP caching. If this is not an option, for example you are on a shared host, then consider enabling the file cache, detailed instructions are on that page.