memcached

An interface to the libmemcached C client.

== License

Copyright 2008 Cloudburst, LLC. Licensed under the AFL 3. See the included LICENSE file. Portions copyright 2008 TangentOrg, Brian Aker, licensed under the BSD license, and used with permission.

The public certificate for this gem is here[http://rubyforge.org/frs/download.php/25331/evan_weaver-original-public_cert.pem]. 

If you use this software, please {make a donation}[http://blog.evanweaver.com/donate/], or {recommend Evan}[http://www.workingwithrails.com/person/7739-evan-weaver] at Working with Rails.

== Features

* clean API
* robust access to all memcached features
* multiple hashing modes, including consistent hashing
* ludicrous speed, including optional non-blocking IO

The <b>memcached</b> library wraps the pure-C libmemcached client via SWIG.

== Installation

You need Ruby 1.8.6, and {libmemcached 0.21}[http://tangent.org/552/libmemcached.html]. Other versions are not supported. You also need {memcached itself}[http://www.danga.com/memcached/] if you want to test against a local server.

For Linux, download and extract the {libmemcached tarball}[http://download.tangent.org/libmemcached-0.21.tar.gz]. Then run:
  ./configure
  make && sudo make install
  
For OS X, you may be able to install it from MacPorts:
  sudo port install libmemcached @0.21
  
Now install the gem:
  sudo gem install memcached --no-rdoc --no-ri
  
Note that on OS X 10.5 you may need to set the architecture explicitly: 
  sudo env ARCHFLAGS="-arch i386" gem install memcached --no-rdoc --no-ri
  
== Usage

Start a local 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:

  start = 1
  $cache.set 'counter', start, 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 <b>Ruby-MemCache</b> or <b>memcache-client</b>. In particular, <tt>nil</tt> is a valid record value. Memcached#get does not return <tt>nil</tt> on failure, rather it raises <b>Memcached::NotFound</b>. 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

== Legacy applications

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

The easiest way to use it in your app is by installing Interlock[http://blog.evanweaver.com/files/doc/fauna/interlock] and setting <tt>client: memcached</tt> in <tt>config/memcached.yml</tt>. This gives you memcached fragments by default. You do not have to use the other Interlock features unless you want to.
  
== Threading

<b>memcached</b> 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'
    # ...
    cache.destroy
  end  

  # Join the thread so that exceptions don't get lost
  thread.join
  
Make sure to call Memcached#destroy before your thread exits or you will leak memory.

== Benchmarks

<b>memcached</b> is up to 150x faster than <b>memcache-client</b>, and up to 15x faster than <b>caffeine</b>. See BENCHMARKS[link:files/BENCHMARKS.html] for details.

== Reporting problems

The support forum is here[http://rubyforge.org/forum/forum.php?forum_id=20894].

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}[http://www.socialtext.net/memcached/index.cgi]
* {Libmemcached homepage}[http://tangent.org/552/libmemcached.html]