Redis

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Wikimedia infrastructure

Data centres and PoPs

Networking

HTTP Caching

MediaWiki


Media

Logs

Redis is used in Wikimedia production for:

  • changeprop (role::redis::misc)
  • stashing user sessions ($wgSessionCacheType) and the data stored in the main stash ($wgMainStash).
  • Maps
  • As a cache and queue backend in ORES
  • Receiver of sampled profile data from PHP, as part as the sampling/profiling pipeline (Arc Lamp).
  • stores lists of articles for new editors to edit as part of the GettingStarted MediaWiki extension

MediaWiki-Vagrant and MediaWiki-Vagrant in Cloud VPS are configured by default to use redis for $wgMainCacheType, $wgSessionCacheType, etc.

Role redis::misc (Redis 3.x)

The role redis::misc is for our general purpose master-slave cluster in eqiad and codfw DCs. Each rdb* node has 5 instances (ports 6378, 6379, 6380, 6381, 6382) because redis is sigle threaded.

Servers

Each master has its respected slave. Masters use odd numbers (e.g. rdb1005) and slaves an even one (e.g. rdb1006). Master-slave instances use the same ports e.g. rdb1005:6379 is the master of rdb1006:6379

eqiad:

  • rdb1005 (m) - rdb1005 (s)
  • rdb1009 (m) - rdb1010 (s)

codfw:

  • rdb2003 (m) - rdb2004 (s)
  • rdb2005 (m) - rdb2006 (s)

Services

Change propagation (or changeprop) is a service running on scb* servers listening to topics on Kafka for events, and translates them into http requests to various systems. It is also responsible for cache evictions to happen on all services like RESTBase. Changeprop talks to redis via Nutcracker.

Related puppet code

  • hieradata/role/common/redis/misc/master.yaml
  • hieradata/role/common/redis/misc/slave.yaml
  • modules/role/manifests/redis/misc/master.pp
  • modules/role/manifests/redis/misc/slave.pp

Other Info

Using Redis

Connecting

redis-cli is installed on all servers where redis-server is installed. This will leave you at a redis prompt where you can enter commands interactively.

Some useful commands

  • AUTH <somepass> authenticate
  • INFO status information, including:
# Replication
role:slave
master_host:10.64.0.24
master_port:6379
master_link_status:up
master_last_io_seconds_ago:0
<snip>
# Keyspace
db0:keys=9351936,expires=9291239,avg_ttl=0
  • KEYS <pattern-here> list of all keys matching the given pattern. Use this sparingly! This query could take seconds to complete
  • QUIT closes the connection.


Other references

Commands are easy, they all depend on the data type (hash, set, list, etc). Here's a quick reference.

Configuration is likewise pretty straightforward with perhaps the exception of the snapshotting, aof and memory settings; here's the sample config file.

See also

  • memcached
  • nutcracker (AKA twemproxy), the proxy used by all application servers to contact memcached (but not redis as of 2015, except it does again as of 2016)