redis-rb

A Ruby client library for Redis.

A Ruby client that tries to match Redis' API one-to-one, while still providing an idiomatic interface. It features thread-safety, client-side sharding, pipelining, and an obsession for performance.

Upgrading from 2.x to 3.0

Please refer to the CHANGELOG for a summary of the most important changes, as well as a full list of changes.

Getting started

To install redis-rb, run the following command:

  gem install redis

Or if you are using bundler, add

  gem 'redis', '~>3.2'

to your Gemfile, and run bundle install

As of version 2.0 this client only targets Redis version 2.0 and higher. You can use an older version of this client if you need to interface with a Redis instance older than 2.0, but this is no longer supported.

You can connect to Redis by instantiating the Redis class:

require "redis"

redis = Redis.new

This assumes Redis was started with a default configuration, and is listening on localhost, port 6379. If you need to connect to a remote server or a different port, try:

redis = Redis.new(:host => "10.0.1.1", :port => 6380, :db => 15)

You can also specify connection options as a redis:// URL:

redis = Redis.new(:url => "redis://:p4ssw0rd@10.0.1.1:6380/15")

By default, the client will try to read the REDIS_URL environment variable and use that as URL to connect to. The above statement is therefore equivalent to setting this environment variable and calling Redis.new without arguments.

To connect to Redis listening on a Unix socket, try:

redis = Redis.new(:path => "/tmp/redis.sock")

To connect to a password protected Redis instance, use:

redis = Redis.new(:password => "mysecret")

The Redis class exports methods that are named identical to the commands they execute. The arguments these methods accept are often identical to the arguments specified on the Redis website. For instance, the SET and GET commands can be called like this:

redis.set("mykey", "hello world")
# => "OK"

redis.get("mykey")
# => "hello world"

All commands, their arguments and return values are documented, and available on rdoc.info.

Sentinel support

The client is able to perform automatic failovers by using Redis Sentinel. Make sure to run Redis 2.8+ if you want to use this feature.

To connect using Sentinel, use:

SENTINELS = [{:host => "127.0.0.1", :port => 26380},
             {:host => "127.0.0.1", :port => 26381}]

redis = Redis.new(:url => "redis://mymaster", :sentinels => SENTINELS, :role => :master)

• The master name identifies a group of Redis instances composed of a master and one or more slaves (mymaster in the example).

• It is possible to optionally provide a role. The allowed roles are master and slave. When the role is slave, the client will try to connect to a random slave of the specified master. If a role is not specified, the client will connect to the master.

• When using the Sentinel support you need to specify a list of sentinels to connect to. The list does not need to enumerate all your Sentinel instances, but a few so that if one is down the client will try the next one. The client is able to remember the last Sentinel that was able to reply correctly and will use it for the next requests.

Storing objects

Redis only stores strings as values. If you want to store an object, you can use a serialization mechanism such as JSON:

require "json"

redis.set "foo", [1, 2, 3].to_json
# => OK

JSON.parse(redis.get("foo"))
# => [1, 2, 3]

Pipelining

When multiple commands are executed sequentially, but are not dependent, the calls can be pipelined. This means that the client doesn't wait for reply of the first command before sending the next command. The advantage is that multiple commands are sent at once, resulting in faster overall execution.

The client can be instructed to pipeline commands by using the #pipelined method. After the block is executed, the client sends all commands to Redis and gathers their replies. These replies are returned by the #pipelined method.

redis.pipelined do
  redis.set "foo", "bar"
  redis.incr "baz"
end
# => ["OK", 1]

Executing commands atomically

You can use MULTI/EXEC to run a number of commands in an atomic fashion. This is similar to executing a pipeline, but the commands are preceded by a call to MULTI, and followed by a call to EXEC. Like the regular pipeline, the replies to the commands are returned by the #multi method.

redis.multi do
  redis.set "foo", "bar"
  redis.incr "baz"
end
# => ["OK", 1]

Futures

Replies to commands in a pipeline can be accessed via the futures they emit (since redis-rb 3.0). All calls inside a pipeline block return a Future object, which responds to the #value method. When the pipeline has successfully executed, all futures are assigned their respective replies and can be used.

redis.pipelined do
  @set = redis.set "foo", "bar"
  @incr = redis.incr "baz"
end

@set.value
# => "OK"

@incr.value
# => 1

Error Handling

In general, if something goes wrong you'll get an exception. For example, if it can't connect to the server a Redis::CannotConnectError error will be raised.

begin
  redis.ping
rescue Exception => e
  e.inspect
# => #<Redis::CannotConnectError: Timed out connecting to Redis on 10.0.1.1:6380>

  e.message
# => Timed out connecting to Redis on 10.0.1.1:6380
end

See lib/redis/errors.rb for information about what exceptions are possible.

Expert-Mode Options

• inherit_socket: true: disable safety check that prevents a forked child from sharing a socket with its parent; this is potentially useful in order to mitigate connection churn when:

  • many short-lived forked children of one process need to talk to redis, AND
  • your own code prevents the parent process from using the redis connection while a child is alive

  Improper use of inherit_socket will result in corrupted and/or incorrect responses.

Alternate drivers

By default, redis-rb uses Ruby's socket library to talk with Redis. To use an alternative connection driver it should be specified as option when instantiating the client object. These instructions are only valid for redis-rb 3.0. For instructions on how to use alternate drivers from redis-rb 2.2, please refer to an older README.

hiredis

The hiredis driver uses the connection facility of hiredis-rb. In turn, hiredis-rb is a binding to the official hiredis client library. It optimizes for speed, at the cost of portability. Because it is a C extension, JRuby is not supported (by default).

It is best to use hiredis when you have large replies (for example: LRANGE, SMEMBERS, ZRANGE, etc.) and/or use big pipelines.

In your Gemfile, include hiredis:

gem "redis", "~> 3.0.1"
gem "hiredis", "~> 0.4.5"

When instantiating the client object, specify hiredis:

redis = Redis.new(:driver => :hiredis)

synchrony

The synchrony driver adds support for em-synchrony. This makes redis-rb work with EventMachine's asynchronous I/O, while not changing the exposed API. The hiredis gem needs to be available as well, because the synchrony driver uses hiredis for parsing the Redis protocol.

In your Gemfile, include em-synchrony and hiredis:

gem "redis", "~> 3.0.1"
gem "hiredis", "~> 0.4.5"
gem "em-synchrony"

When instantiating the client object, specify synchrony:

redis = Redis.new(:driver => :synchrony)

Testing

This library is tested using Travis, where it is tested against the following interpreters and drivers:

• MRI 1.8.7 (drivers: ruby, hiredis)
• MRI 1.9.2 (drivers: ruby, hiredis, synchrony)
• MRI 1.9.3 (drivers: ruby, hiredis, synchrony)
• MRI 2.0.0 (drivers: ruby, hiredis, synchrony)
• JRuby 1.7 (1.8 mode) (drivers: ruby)
• JRuby 1.7 (1.9 mode) (drivers: ruby)

Contributors

(ordered chronologically with more than 5 commits, see git shortlog -sn for all contributors)

• Ezra Zygmuntowicz
• Taylor Weibley
• Matthew Clark
• Brian McKinney
• Luca Guidi
• Salvatore Sanfilippo
• Chris Wanstrath
• Damian Janowski
• Michel Martens
• Nick Quaranto
• Pieter Noordhuis
• Ilya Grigorik

Contributing

Fork the project and send pull requests. You can also ask for help at #redis-rb on Freenode.