Redis

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

Setup
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:

In your "LocalSettings.php" file, set:


 * Parameters explained
 * : 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.
 * : The timeout for new connections, in seconds. Optional, default is 1 second.
 * : Set this to true to allow connections to persist across multiple web requests. False by default.
 * : The authentication password, will be sent to Redis in clear text. Optional, if it is unspecified, no AUTH command will be sent.
 * : 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. If you'd like to use Redis as the default cache for various data, you may set any of the following configuration options:

Job queue

 * Parameters explained
 * : An array of parameters to RedisConnectionPool::__construct. Note that the serializer option is ignored as "none" is always used. If the same Redis server is used as for, the Redis password needs to be set here as well (see   config above).
 * : 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.
 * : The type of compression to use; one of (none,gzip).
 * : 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 Redis

 * 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.

General

 * Official site (see esp. Introduction to Redis)
 * The Redis article on the English Wikipedia.
 * Redis Watch - an e-mail round-up of Redis news, articles, tools and libraries
 * Redis/INCR
 * Getting to Know Redis
 * Redis, from the Ground Up
 * Redis and Relational Data
 * Redis Cookbook (book; not great, but see ch. "Analytics and Time-Based Data")
 * Interview with Salvatore Sanfilippo (code-oriented but still useful)
 * Redis DB (Google Group)

Analytics

 * Redis at Disqus (their entire analytics platform runs on Redis)
 * Effective Web App Analytics with Redis
 * How YouPorn uses Redis (video)
 * Realtime metrics using Redis bitmaps

Tooling

 * Redily fully-featured, cross-platform Redis GUI Client
 * Redsmin a real-time, atomic, performant administration and monitoring interface for Redis
 * redis-py is the library of choice for Python
 * Getting Started: Redis and Python
 * Redis and Python (presentation slides)
 * Resque for jobs
 * Redisco, a Python ORM for Redis
 * py-analytics (I haven't used this)
 * redis-bitops Ruby gem for sparse bitmap operations

Informed Opinions

 * Antirez: You Need To Think In Terms Of Organizing Your Data For Fetching

Miscellaneous

 * Storing hundreds of millions of simple key-value pairs (how Instagram uses Redis)
 * Key performance metrics to monitor for Redis