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



If you have not 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 with the following command:

apt-get install redis-server php-redis

In your "LocalSettings.php" file, set:

$wgObjectCaches['redis'] = array(
    'class'                => 'RedisBagOStuff',
    'servers'              => array( '' ),
    // 'connectTimeout'    => 1,
    // 'persistent'        => false,
    // 'password'          => 'secret',
    // 'automaticFailOver' => true,
Parameters explained
  • servers: An array of server names. A server name may be a hostname, a hostname/port combination or the absolute path of a UNIX socket. If a hostname is specified but no port, the standard port number 6379 will be used. Arrays keys can be used to specify the tag to hash on in place of the host/port. Required.
  • connectTimeout: The timeout for new connections, in seconds. Optional, default is 1 second.
  • persistent: Set this to true to allow connections to persist across multiple web requests. False by default.
  • password: The authentication password, will be sent to Redis in clear text. Optional, if it is unspecified, no AUTH command will be sent.
  • automaticFailover: If this is false, then each key will be mapped to a single server, and if that server is down, any requests for that key will fail. If this is true, a connection failure will cause the client to immediately try the next server in the list (as determined by a consistent hashing algorithm). True by default. This has the potential to create consistency issues if a server is slow enough to flap, for example if it is in swap death. True by default.

You will 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';

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

Job queueEdit

$wgJobTypeConf['default'] = [
    'class'          => 'JobQueueRedis',
    'redisServer'    => '',
    'redisConfig'    => [],
    'claimTTL'       => 3600,
    'daemonized'     => true
Parameters explained
  • redisConfig: An array of parameters to RedisConnectionPool::__construct(). Note that the serializer option is ignored as "none" is always used.
  • redisServer: A hostname/port combination or the absolute path of a UNIX socket. If a hostname is specified but no port, the standard port number 6379 will be used. Required.
  • compression: The type of compression to use; one of (none,gzip).
  • daemonized: Set to true if the redisJobRunnerService runs in the background. This will disable job recycling/undelaying from the MediaWiki side to avoid redundance and out-of-sync configuration.

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

MediaWiki & Wikimedia use cases for RedisEdit

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.
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 readingEdit




Informed OpinionsEdit