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MediaWiki uses several independent caching layers to reduce database load and improve response times. Understanding which layer to configure is key to scaling a wiki.

Object Cache

General-purpose key-value store for arbitrary data. Configured via $wgMainCacheType. Backends include APCu, Memcached, and Redis.

WAN Object Cache

A distributed cache layer built on top of the object cache. Handles cross-datacenter invalidation and stampede protection.

Parser Cache

Stores the rendered HTML output of wikitext pages. Configured via $wgParserCacheType. Avoids re-parsing unchanged pages.

CDN / Squid

An HTTP reverse proxy cache in front of MediaWiki. MediaWiki sends Purge requests to CDN servers when pages change.

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$wgMainCacheType

The primary object cache is controlled by $wgMainCacheType. MediaWiki also uses $wgMessageCacheType and $wgParserCacheType for more specific caches, which fall back to $wgMainCacheType if not set independently.
ConstantDescription
CACHE_NONENo caching (default; suitable for development only)
CACHE_DBStore in the database objectcache table (always available, but slow)
CACHE_ACCELUse a PHP opcode cache extension: APCu if available, else falls back
CACHE_MEMCACHEDUse Memcached servers listed in $wgMemCachedServers
CACHE_ANYTHINGUse the best available cache; falls back to CACHE_DB if nothing else configured
'redis'Use a Redis backend defined in $wgObjectCaches
// LocalSettings.php

// Use APCu (single-server deployments)
$wgMainCacheType = CACHE_ACCEL;

// Use Memcached
$wgMainCacheType = CACHE_MEMCACHED;
$wgMemCachedServers = [ '127.0.0.1:11211' ];

// Use Redis (custom key in $wgObjectCaches)
$wgMainCacheType = 'redis';

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Local Server Cache (APCu)

APCu stores data in shared memory on the local server. It is the fastest option for single-server setups, but data is not shared between servers. 
// Enable APCu as the main cache
$wgMainCacheType = CACHE_ACCEL;
APCu is only suitable when all web requests are served from a single server. In a multi-server setup, use Memcached or Redis so all servers share the same cache.

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Memcached

// Single Memcached server
$wgMainCacheType    = CACHE_MEMCACHED;
$wgMemCachedServers = [ '127.0.0.1:11211' ];

// Multiple servers with weights
$wgMemCachedServers = [
    '10.0.0.1:11211',
    '10.0.0.2:11211',
    '10.0.0.3:11211',
];

// Persistent connections (recommended)
$wgMemCachedPersistent = true;

// Timeout in microseconds
$wgMemCachedTimeout = 500000; // 0.5 seconds

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Redis

Redis is configured by adding an entry to $wgObjectCaches and then referencing it by key: 
// Define a Redis cache backend
$wgObjectCaches['redis'] = [
    'class'       => 'RedisBagOStuff',
    'servers'     => [ '127.0.0.1:6379' ],
    'persistent'  => true,
    'password'    => null,   // set if Redis requires AUTH
    'connectTimeout' => 2,
    'readTimeout'    => 2,
];

// Use it as the main cache
$wgMainCacheType = 'redis';

// Optionally use it for the session store as well
$wgSessionCacheType = 'redis';

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WAN Object Cache

WANObjectCache is a distributed caching abstraction that sits on top of any BagOStuff backend. It provides:
  • Multi-key reads for efficiency
  • Check-and-set to prevent cache poisoning
  • Stampede protection with probabilistic early expiry
  • Cross-datacenter invalidation via version numbers
The WAN cache is used throughout MediaWiki core for data that must be consistent across multiple servers. It is automatically wired to $wgMainCacheType. 
// Accessing WANObjectCache in extension code
$wanCache = MediaWikiServices::getInstance()->getMainWANObjectCache();

$value = $wanCache->getWithSetCallback(
    $wanCache->makeKey( 'myext', 'mydata', $id ),
    WANObjectCache::TTL_DAY,
    function ( $oldValue, &$ttl, array &$setOpts ) use ( $id ) {
        // This callback runs when the cache misses
        $setOpts += Database::getCacheSetOptions( wfGetDB( DB_REPLICA ) );
        return expensiveLookup( $id );
    }
);

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Parser Cache

The parser cache stores the HTML output from rendering wikitext. When a page is requested, MediaWiki checks the parser cache first and only re-parses if the cache is stale or missing. 
// Use a dedicated cache for parser output (optional; defaults to $wgMainCacheType)
$wgParserCacheType = CACHE_MEMCACHED;

// Parser cache expiry in seconds (default: 1 day)
$wgParserCacheExpireTime = 86400;

// Message cache expiry
$wgMessageCacheType   = CACHE_ACCEL;
$wgMsgCacheExpiry     = 86400;
For wikis where most pages rarely change, increasing $wgParserCacheExpireTime reduces re-parse frequency and database load. Pages are always invalidated immediately when edited.

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CDN / Squid Integration

MediaWiki can purge cached pages from CDN/Varnish/Squid servers when content changes. Set $wgUseCdn = true and list your servers: 
// Enable CDN support
$wgUseCdn = true;

// Single CDN/Varnish server
$wgCdnServers = [ '10.0.0.10' ];

// Maximum age for cached pages (seconds)
$wgSquidMaxage = 18000;

// Shared cache via HTCP multicast (for Squid clusters)
$wgHTCPRouting = [
    '' => [ 'host' => '239.128.0.112', 'port' => 4827 ],
];
When a page is edited, MediaWiki automatically sends HTTP PURGE requests to the listed CDN servers for all affected URLs.

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Purging Caches

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Purge Specific Pages

# Purge a list of URLs from the CDN/file cache
php maintenance/run.php purgeList --titles page-list.txt

# Purge a single page
php maintenance/run.php purgePage --title "Main_Page"

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Purge the Parser Cache

# Delete all entries from the parser cache older than 1 day
php maintenance/run.php purgeParserCache --age 86400

# Delete entries for a specific namespace
php maintenance/run.php purgeParserCache --namespace 0

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Rebuild the File Cache

# Rebuild the static HTML file cache for the main namespace
php maintenance/run.php rebuildFileCache --namespace 0

# Prune stale entries from the file cache
php maintenance/run.php pruneFileCache

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Purge Changed Files

# Purge CDN cache for files changed since a timestamp
php maintenance/run.php purgeChangedFiles --starttime 20240101000000

# Purge CDN cache for pages changed since a timestamp
php maintenance/run.php purgeChangedPages --starttime 20240101000000

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Rebuild Localisation Cache

# Rebuild the localisation cache (run after updating MediaWiki or extensions)
php maintenance/run.php rebuildLocalisationCache

# Rebuild for a specific language only
php maintenance/run.php rebuildLocalisationCache --lang fr

// LocalSettings.php — production multi-server setup

// Shared object cache via Memcached
$wgMainCacheType    = CACHE_MEMCACHED;
$wgMemCachedServers = [ '10.0.0.1:11211', '10.0.0.2:11211' ];
$wgMemCachedPersistent = true;

// Parser cache also uses Memcached
$wgParserCacheType    = CACHE_MEMCACHED;
$wgParserCacheExpireTime = 3600 * 24; // 1 day

// CDN integration
$wgUseCdn     = true;
$wgCdnServers = [ '10.0.0.10', '10.0.0.11' ];
$wgSquidMaxage = 18000;

// Disable inline job execution (use cron instead)
$wgJobRunRate = 0;

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