memcached

An interface to the libmemcached C client.

License¶ ↑

Copyright 2009-2011 Cloudburst, LLC. Licensed under the AFL 3. See the included LICENSE file. Portions copyright 2007-2009 TangentOrg, Brian Aker, licensed under the BSD license, and used with permission.

Features¶ ↑

• clean API

• robust access to all memcached features

• SASL support for the binary protocol

• multiple hashing modes, including consistent hashing

• ludicrous speed, including optional pipelined IO with no_reply

The memcached library wraps the pure-C libmemcached client via SWIG.

Installation¶ ↑

You need Ruby 1.8.7 or Ruby 1.9.2. Other versions may work, but are not guaranteed. You also need the ‘libsasl2-dev` and `gettext` libraries, which should be provided through your system’s package manager.

Install the gem:

sudo gem install memcached --no-rdoc --no-ri

Usage¶ ↑

Start a local networked memcached server:

$ memcached -p 11211 &

Now, in Ruby, require the library and instantiate a Memcached object at a global level:

require 'memcached'
$cache = Memcached.new("localhost:11211")

Now you can set things and get things:

value = 'hello'
$cache.set 'test', value
$cache.get 'test' #=> "hello"

You can set with an expiration timeout:

value = 'hello'
$cache.set 'test', value, 1
sleep(2)
$cache.get 'test' #=> raises Memcached::NotFound

You can get multiple values at once:

value = 'hello'
$cache.set 'test', value
$cache.set 'test2', value
$cache.get ['test', 'test2', 'missing']
  #=> {"test" => "hello", "test2" => "hello"}

You can set a counter and increment it. Note that you must initialize it with an integer, encoded as an unmarshalled ASCII string:

start = 1
$cache.set 'counter', start.to_s, 0, false
$cache.increment 'counter' #=> 2
$cache.increment 'counter' #=> 3
$cache.get('counter', false).to_i #=> 3

You can get some server stats:

$cache.stats #=> {..., :bytes_written=>[62], :version=>["1.2.4"] ...}

Note that the API is not the same as that of Ruby-MemCache or memcache-client. In particular, nil is a valid record value. Memcached#get does not return nil on failure, rather it raises Memcached::NotFound. This is consistent with the behavior of memcached itself. For example:

$cache.set 'test', nil
$cache.get 'test' #=> nil
$cache.delete 'test'
$cache.get 'test' #=> raises Memcached::NotFound

Rails¶ ↑

# config/environment.rb
require "memcached/rails"
config.cache_store = Memcached::Rails.new(:servers => ['127.0.0.1'])

Pipelining¶ ↑

Pipelining updates is extremely effective in memcached, leading to more than 25x write throughput than the default settings. Use the following options to enable it:

:no_block => true,
:buffer_requests => true,
:noreply => true,
:binary_protocol => false

Currently #append, #prepend, #set, and #delete are pipelined. Note that when you perform a read, all pending writes are flushed to the servers.

Threading¶ ↑

memcached is threadsafe, but each thread requires its own Memcached instance. Create a global Memcached, and then call Memcached#clone each time you spawn a thread.

thread = Thread.new do
  cache = $cache.clone
  # Perform operations on cache, not $cache
  cache.set 'example', 1
  cache.get 'example'
end

# Join the thread so that exceptions don't get lost
thread.join

Legacy applications¶ ↑

There is a compatibility wrapper for legacy applications called Memcached::Rails.

Benchmarks¶ ↑

memcached, correctly configured, is at least twice as fast as memcache-client and dalli. See BENCHMARKS for details.

Reporting problems¶ ↑

The support forum is here.

Patches and contributions are very welcome. Please note that contributors are required to assign copyright for their additions to Cloudburst, LLC.

Further resources¶ ↑

• Memcached wiki

• Libmemcached homepage