Redis

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Redis is an open-source, networked, in-memory, key-value data store with optional durability, written in ANSI C.

Setup[edit]

If you haven't already, you'll need to configure a Redis instance and install a Redis client library for PHP. Most environments require the phpredis PHP extension. On Debian / Ubuntu, you can install the requirements via apt-get install redis-server php-redis. If you're running MediaWiki on top of HHVM (unlikely unless you're a developer), you can use the Redis client library that comes with HHVM instead.

In your LocalSettings.php file, set:

/** @see RedisBagOStuff for a full explanation of these options. **/
$wgObjectCaches['redis'] = array(
    'class'                => 'RedisBagOStuff',
    'servers'              => array( '127.0.0.1:6379' ),
    // 'connectTimeout'    => 1,
    // 'persistent'        => false,
    // 'password'          => 'secret',
    // 'automaticFailOver' => true,
);

You'll now be able to acquire a Redis object cache object via wfGetCache( 'redis' ). If you'd like to use Redis as the default cache for various data, you may set any of the following configuration options:

$wgMainCacheType = 'redis';
$wgSessionCacheType = 'redis';  // same as WMF prod

// Not widely tested:
$wgMessageCacheType = 'redis';
$wgParserCacheType = 'redis';
$wgLanguageConverterCacheType = 'redis';

Job queue[edit]

$wgJobTypeConf['default'] = [
    'class'          => 'JobQueueRedis',
    'redisServer'    => '127.0.0.1:6379',
    'redisConfig'    => [],
    'claimTTL'       => 3600,
    'daemonized'     => true
 ];

From that moment, jobs will be delivered to the Redis instance run the specified server.

MediaWiki & Wikimedia use cases for Redis[edit]

Session storage
The Wikimedia Foundation has been using Redis as a memcached replacement for session storage since the eqiad switchover in January 2013, because it has a replication feature which can be used to synchronise data between the two data centres. It allowed us to switch from Tampa to Ashburn without logging everyone out.
Job queue
We previously stored the MW job queue in MySQL. This gave us lots of useful features, like replication and indexing for duplicate removal, but it has often been hard to manage the performance implications of the high insert rate. Among its many features, Redis embeds a Lua interpreter on the server side. The new Redis job queue class provides a rich feature set superior to the MySQL job queue, mainly through several server-side Lua scripts which provide high-level job queue functions. Redis is also used to keep a hash table that tracks which job queues actually have jobs, so runners know where to look. Updates to this table are push-based, so it is always up-to-date.
Features
Extension:GettingStarted's early implementation of a category-based recommender system has used Redis to store a list of tasks (actually page ids) served via a few interfaces.

Further reading[edit]

General[edit]

Analytics[edit]

Tooling[edit]

Informed Opinions[edit]

Miscellaneous[edit]