Dalli

Dalli is a high performance pure Ruby client for accessing memcached servers. It works with memcached 1.4+ only as it uses the newer binary protocol. It should be considered a replacement for the memcache-client gem. The API tries to be mostly compatible with memcache-client with the goal being to make it a drop-in replacement for Rails.

The name is a variant of Salvador Dali for his famous painting The Persistence of Memory.

Dalli's development is sponsored by NorthScale. Many thanks to them!

Design

I decided to write Dalli after maintaining memcache-client for the last two years for a few specific reasons:

The code is mostly old and gross. The bulk of the code is a single 1000 line .rb file.
It has a lot of options that are infrequently used which complicate the codebase.
The implementation has no single point to attach monitoring hooks.
Uses the old text protocol, which hurts raw performance.

So a few notes. Dalli:

uses the exact same algorithm to choose a server so existing memcached clusters with TBs of data will work identically to memcache-client.
is approximately 20% faster than memcache-client (which itself was heavily optimized) in Ruby 1.9.2.
contains explicit "chokepoint" methods which handle all requests; these can be hooked into by monitoring tools (NewRelic, Rack::Bug, etc) to track memcached usage.
comes with hooks to replace memcache-client in Rails.
is approx 700 lines of Ruby. memcache-client is approx 1250 lines.
supports SASL for use in managed environments, e.g. Heroku.

Installation and Usage

Remember, Dalli requires memcached 1.4+. You can check the version with memcached -h.

gem install dalli

require 'dalli'
dc = Dalli::Client.new('localhost:11211')
dc.set('abc', 123)
value = dc.get('abc')

The test suite requires memcached 1.4.3+ with SASL enabled (./configure --enable-sasl). Currently only supports the PLAIN mechanism.

Usage with Rails 3.0

In your Gemfile:

gem 'dalli'

In config/environments/production.rb:

config.cache_store = :dalli_store

A more comprehensive example (note that we are setting a reasonable default for maximum cache entry lifetime (one day), enabling compression for large values, and namespacing all entries for this rails app. Remove the namespace if you have multiple apps which share cached values):

config.cache_store = :dalli_store, 'cache-1.example.com', 'cache-2.example.com',
    :namespace => NAME_OF_RAILS_APP, :expires_in => 1.day, :compress => true, :compress_threshold => 64.kilobytes

Usage with Rails 2.3.x

In config/environment.rb:

config.gem 'dalli'

In config/environments/production.rb:

require 'active_support/cache/dalli_store23'
config.cache_store = :dalli_store

Usage with Passenger

Put this at the bottom of config/environment.rb:

if defined?(PhusionPassenger)
  PhusionPassenger.on_event(:starting_worker_process) do |forked|
    # Only works with DalliStore
    Rails.cache.reset if forked
  end
end

Features and Changes

Dalli is NOT 100% API compatible with memcache-client. If you have code which uses the MemCache API directly, it will likely need small tweaks. Method parameters and return values changed slightly.

memcache-client allowed developers to store either raw or marshalled values with each API call. I feel this is needless complexity; Dalli allows you to control marshalling per-Client with the :marshal => false flag but you cannot explicitly set the raw flag for each API call. By default, marshalling is enabled.

I've removed support for key namespaces and automatic pruning of keys longer than 250 characters. ActiveSupport::Cache implements these features so there is little need for Dalli to reinvent them.

By default, Dalli is thread-safe. Disable thread-safety at your own peril.

Note that Dalli does not require ActiveSupport or Rails. You can safely use it in your own Ruby projects.

Helping Out

If you have a fix you wish to provide, please fork the code, fix in your local project and then send a pull request on github. Please ensure that you include a test which verifies your fix and update History.md with a one sentence description of your fix so you get credit as a contributor.

Thanks

Brian Mitchell - for his remix-stash project which was helpful when implementing and testing the binary protocol support.

Author

Mike Perham, mperham@gmail.com, mikeperham.com, @mperham If you like and use this project, please give me a recommendation at WWR. Happy caching!

lomography/dalli