MemCachier

Last Updated: 18 February 2014

MemCachier is an implementation of the Memcache in-memory key/value store used for caching data. It is a key technology in modern web applications for scaling and reducing server loads. The MemCachier add-on manages and scales clusters of memcache servers so you can focus on your app. Tell us how much memory you need and get started for free instantly. Add capacity later as you need it.

Getting started

Start by installing the add-on:

$ heroku addons:add memcachier:dev

You can start with more memory if you know you’ll need it:

$ heroku addons:add memcachier:100
$ heroku addons:add memcachier:500
 ... etc ...

Once the add-on has been added you’ll notice three new variables in heroku config:

$ heroku config
...
MEMCACHIER_SERVERS    => mcX.ec2.memcachier.com
MEMCACHIER_USERNAME   => bobslob
MEMCACHIER_PASSWORD   => l0nGr4ndoMstr1Ngo5strang3CHaR4cteRS
...

Next, setup your app to start using the cache. We have documentation for the following languages and frameworks:

• Ruby
• Rails 3 & 4
• Rails 2
• Django
• PHP
• Node.js
• Java

Ruby

Start by adding the memcachier and dalli gems to your Gemfile.

gem 'memcachier'
gem 'dalli'

Then bundle install:

$ bundle install

Dalli is a Ruby memcache client, and the memcachier gem modifies the environment (ENV) such that the environment variables set by MemCachier will work with Dalli. Once these gems are installed you can start writing code. The following is a basic example showing get and set.

require 'dalli'
require 'memcachier'
cache = Dalli::Client.new
cache.set("foo", "bar")
puts cache.get("foo")

Without the memcachier gem, you’ll need to pass the proper credentials to Dalli:

cache = Dalli::Client.new(ENV["MEMCACHIER_SERVERS"].split(","),
                    {:username => ENV["MEMCACHIER_USERNAME"],
                     :password => ENV["MEMCACHIER_PASSWORD"],
                     :failover => true,
                     :socket_timeout => 1.5,
                     :socket_failure_delay => 0.2
                    })

Testing (Ruby)

The easiest way to test that your setup is working is through the heroku console:

$ heroku run console --app <app>
>> require 'dalli'
>> require 'memcachier'
>> dc = Dalli::Client.new
>> dc.set('memcachier', 'rocks')
=> true

And then fetch the value back:

>> dc.get('memcachier')
=> "rocks"

You can also get an insight into your cache usage (number of keys stored and bytes) with the stats command:

>> dc.stats
=> {"memcachier.example.net:11211" => {"cur_items" => "49982", "bytes" => "89982234"} }

Rails 3 and 4

Below explains how to setup and install MemCachier with Rails. Refer to the Rails caching guide for information on how to use MemCachier with Rails. Rails supports automatic whole site caching, per-view caching and fragement caching.

Start by adding the memcachier and dalli gems to your Gemfile.

gem 'memcachier'
gem 'dalli'

Then run bundle install:

$ bundle install

Dalli is a Ruby memcache client, and the memcachier gem modifies the environment (ENV) such that the environment variables set by MemCachier will work with Dalli. Once these gems are installed you’ll want to configure the Rails cache_store appropriately. Modify config/environments/production.rb with the following:

config.cache_store = :dalli_store

From here you can use the following code examples to use the cache in your Rails app:

Rails.cache.write("foo", "bar")
puts Rails.cache.read("foo")

Without the memcachier gem, you’ll need to pass the proper credentials to Dalli in config/environments/production.rb:

config.cache_store = :dalli_store,
                    (ENV["MEMCACHIER_SERVERS"] || "").split(","),
                    {:username => ENV["MEMCACHIER_USERNAME"],
                     :password => ENV["MEMCACHIER_PASSWORD"],
                     :failover => true,
                     :socket_timeout => 1.5,
                     :socket_failure_delay => 0.2
                    }

Testing (Rails)

To test locally you can simply use the rails console:

rails console
>> Rails.cache.write('memcachier', 'rocks')
=> true
>> Rails.cache.read('memcachier')
=> "rocks"

To test against MemCachier itself, please refer to the Ruby testing instructions.

Rails 2

Start by adding the memcachier and dalli gems to your Gemfile. You will need to use dalli v1.0.5 as later versions of Dalli don’t support Rails 2.

gem 'memcachier'
gem 'dalli', '~>1.0.5'

Then run bundle install:

$ bundle install

Dalli is a Ruby memcache client, and the memcachier gem modifies the environment (ENV) such that the environment variables set by MemCachier will work with Dalli. Once these gems are installed you’ll want to configure the Rails cache_store appropriately. Modify config/environments/production.rb with the following:

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

In config/environment.rb:

config.gem 'dalli'

From here you can use the following code examples to use the cache in your Rails app:

Rails.cache.write("foo", "bar")
puts Rails.cache.read("foo")

Without the memcachier gem, you’ll need to pass the proper credentials to Dalli in config/environments/production.rb:

config.cache_store = :dalli_store,
                    (ENV["MEMCACHIER_SERVERS"] || "").split(","),
                    {:username => ENV["MEMCACHIER_USERNAME"],
                     :password => ENV["MEMCACHIER_PASSWORD"],
                     :failover => true,
                     :socket_timeout => 1.5,
                     :socket_failure_delay => 0.2
                    }

Testing (Rails)

To test locally you can simply use the rails console:

rails console
>> Rails.cache.write('memcachier', 'rocks')
=> true
>> Rails.cache.read('memcachier')
=> "rocks"

To test against MemCachier itself, please refer to the Ruby testing instructions.

Rails Rack::Cache

Rails can use a middle-ware component of the Rack web server architecture called Rack::Cache. This provides caching of static assets in Rails and is a simple alternative to use a full CDN.

Please see this article for information.

Django

Below explains how to setup and install MemCachier with Django. Please refer to the Django caching guide for information on how to effectively use MemCachier. Django supports whole site caching, per-view caching and fragement caching.

MemCachier has been tested with the pylibmc memcache client, but the default client doesn’t support SASL authentication. Run the following commands on your local machine to install the necessary pips:

$ sudo port install libmemcached
$ LIBMEMCACHED=/opt/local pip install pylibmc
$ pip install django-pylibmc-sasl

Be sure to update your requirements.txt file with these new requirements (note that your versions may differ than what’s below):

pylibmc==1.2.2
django-pylibmc-sasl==0.2.4

Next, configure your settings.py file the following way:

os.environ['MEMCACHE_SERVERS'] = os.environ.get('MEMCACHIER_SERVERS', '').replace(',', ';')
os.environ['MEMCACHE_USERNAME'] = os.environ.get('MEMCACHIER_USERNAME', '')
os.environ['MEMCACHE_PASSWORD'] = os.environ.get('MEMCACHIER_PASSWORD', '')

CACHES = {
  'default': {
    'BACKEND': 'django_pylibmc.memcached.PyLibMCCache',
    'TIMEOUT': 1000,
    'BINARY': True,
    'OPTIONS': {
        'tcp_nodelay': True,
        'remove_failed': 4
    }
  }
}

From here you can start writing cache code in your Django app:

from django.core.cache import cache
cache.set("foo", "bar")
print cache.get("foo")

You may be interested in the django-heroku-memcacheify pip, which fully configures MemCachier with one line of code for any Django app the pip supports.

PHP

We recommend users utilize the PHPMemcacheSASL client as we have more experience in using and supporting it. Start by downloading the PHPMemcacheSASL library. From here you can start writing cache code in your PHP app:

include('MemcacheSASL.php');
$m = new MemcacheSASL;
$servers = explode(",", getenv("MEMCACHIER_SERVERS"));
foreach ($servers as $s) {
    $parts = explode(":", $s);
    $m->addServer($parts[0], $parts[1]);
}
$m->setSaslAuthData(getenv("MEMCACHIER_USERNAME"), getenv("MEMCACHIER_PASSWORD"));

$m->add("foo", "bar");
echo $m->get("foo");

The more common PHP memcache clients have limited support for working with MemCachier due to issues with SASL authentication. The Memcache simply doesn’t provide SASL authentication support and so is not an option. The Memcached, does provide SASL authentication and so is a fine option for using with MemCachier. We simply have less experience in using it at this time and so continue to recommend PHPMemcacheSASL.

Node.js

For Node.js we recommend the use of the memjs client library. It is written and supported by MemCachier itself! To install, use the node package manager (npm):

npm install memjs

Using it is straight-forward as memjs understands the MEMCACHIER_SERVERS, MEMCACHIER_USERNAME and MEMCACHIER_PASSWORD environment variables that the MemCachier add-on setups. For example:

var memjs = require('memjs')
var mc = memjs.Client.create()
mc.get('hello', function(val) {
    alert(val)
})

Java

For Java we recommend using the SpyMemcached client. We also recommend using the Apache Maven build manager for working with Java applications. If you aren’t using maven and are instead using Apache Ant or your own build system, then simply add the spymemcached jar file as a dependency of your application.

For maven however, start by configuring it to have the proper spymemcached repository:

<repository>
  <id>spy</id>
  <name>Spy Repository</name>
  <layout>default</layout>
  <url>http://files.couchbase.com/maven2/</url>
  <snapshots>
    <enabled>false</enabled>
  </snapshots>
</repository>

Then add the spymemcached library to your dependencies:

<dependency>
  <groupId>spy</groupId>
  <artifactId>spymemcached</artifactId>
  <version>2.8.9</version>
  <scope>provided</scope>
</dependency>

Once your build system is configured, you can start adding caching to your Java app:

import java.io.IOException;
import net.spy.memcached.AddrUtil;
import net.spy.memcached.MemcachedClient;
import net.spy.memcached.ConnectionFactoryBuilder;
import net.spy.memcached.auth.PlainCallbackHandler;
import net.spy.memcached.auth.AuthDescriptor;

public class Foo {
  public static void main(String[] args) {
    AuthDescriptor ad = new AuthDescriptor(new String[] { "PLAIN" },
        new PlainCallbackHandler(System.getenv("MEMCACHIER_USERNAME"),
            System.getenv("MEMCACHIER_PASSWORD")));

    try {
      MemcachedClient mc = new MemcachedClient(
          new ConnectionFactoryBuilder()
              .setProtocol(ConnectionFactoryBuilder.Protocol.BINARY)
              .setAuthDescriptor(ad).build(),
          AddrUtil.getAddresses(System.getenv("MEMCACHIER_SERVERS")));
      mc.set("foo", "bar");
      System.out.println(mc.get("foo"));
    } catch (IOException ioe) {
      System.err.println("Couldn't create a connection to MemCachier: \nIOException "
              + ioe.getMessage());
    }
  }
}

You may wish to look the spymemcached JavaDocs or some more example code to help in using MemCachier effectively. There is also a guide on using WebRunner, Heroku’s framework to handle sessions with MemCachier.

Library support

MemCachier will work with any memcached binding that supports SASL authentication and the binary protocol. We have tested MemCachier with the following language bindings, although the chances are good that other SASL binary protocol packages will also work.

Sample apps

We’ve built a number of working sample apps, too:

• Sinatra Example
• Rails Example
• Django Example
• PHP Example
• Node.js Example
• Java Example

Local usage

To test your Heroku application locally, you will need to run a local memcached server. MemCachier can only run in Heroku, but because MemCachier and memcached speak the same protocol, you shouldn’t have any issues testing locally. Installation depends on your platform.

On Ubuntu:

$ sudo apt-get install memcached

Or on OS X (with Homebrew):

$ brew install memcached

Or for Windows please refer to these instructions.

For further information and resources (such as the memcached source code) please refer to the Memcache.org homepage

To run memcached simply execute the following command:

$ memcached -v

Usage analytics

Our analytics dashboard is a simple tool that gives you more insight into how you’re using memcache. Here’s a screenshot of the dashboard:

To access your application’s analytics dashboard run:

$ heroku addons:open memcachier

Or open MemCachier from your application’s dashboard on heroku.com.

The analytics displayed are:

• Limit – Your current cache size and memory limit. Once usage comes close to this amount you will start seeing evictions.
• Live Connections – Number of connections currently open to your cache.
• Total connections – Number of connections ever made to your cache. (So always larger than live connections).
• Items – Number of items currently stored in your cache.
• Evictions – Number of items ever evicted from your cache due to memory pressure. Items are evicted in an LRU order.
• New Evictions – Number of evictions that have occured since the last time we sampled your cache.
• Hit Rate – The ratio of get commands that return an item (hit) vs. the number that return nothing (miss). This ratio is for the period between now and when we last sampled your cache.
• Set Cmds – Number of times you have ever performed a set command.
• Flush Cmds – Number of times you have ever performned a flush command.

With the basic analytics dashboard we sample your cache once per hour. With the advance dashboard we sample it once every 30 minutes.

Advanced analytics

We offer higher paying customers an advance version of our analytics dashboard. Currently, this offers two primary advantages:

• Higher Sample Rate – We sample the cache for collecting analytics once every thirty minutes, twice the rate of the basic analytics dashboard. We don’t sample more often than that as a higher granularity hasn’t proven to be useful, instead creating more data that has more noise and less signal.
• More Graphs – We offer two additional graphs for the advanced analytics dashboard.
  • Eviction Graph – Your new evictions tracked over time.
  • Connection Graph – Your new connecions tracked over time.

Upgrading and downgrading

Changing your plan, either by upgrading or downgrading, can be done easily at any time through Heroku.

• No code changes are required.
• Your cache won’t be lost or reset*.
• You are charged by the hour for plans, so try experimenting with different cache sizes with low cost.

Using MemCachier

Please refer to your client or framework documentation for how to use MemCachier effectively. We have also written a guide on advanced memcache usage.

Framework and Client Documentation:

• Dalli (Ruby Client) API
• Rails Caching Guide
• Django Caching Guide
• Pylibmc (Pytnon Client) API
• PHPMemcacheSASL API
• MemJS (node.js client) API
• Spymemcached JavaDocs

Key-Value size limit (1MB)

MemCachier has a maximum size that a key-value object can be of 1MB. This applies to both key-value pairs created through a set command, or existing key-value pairs grown through the use of an append or prepend command. In the later case, the size of the key-value pair with the new data added to it, must still be less than 1MB.

The 1MB limit applies to the size of the key and the value together. A key of size 512KB with a value of 712KB would be in violation of the 1MB limit.

The reason for this has partially to do with how memory is managed in MemCachier. A limitation of the high performance design is a restriction on how large key-value pairs can become. Another reason is that storing values larger than 1MB doesn’t normally make sense in a high-performance key-value store. The network transfer time in these situations becomes the limiting factor for performance. A disk cache or even a database makes sense for this size value.

Errors about app trying to connect to localhost

By default, most memcache client look for the environment variables, MEMCACHE_SERVERS, MEMCACHE_USERNAME and MEMCACHE_PASSWORD for their configuration. These variables are used when the initialization code for the memcache client doesn’t specifically specify these values.

If these environment variables aren’t set, clients generally default to connecting to 127.0.0.1:11211 (i.e., localhost), with no username and password.

The MemCachier add-on sets the MEMCACHIER_SERVERS, MEMCACHIER_USERNAME and MEMCACHIER_PASSWORD environment variables. So you need to either set the equivalent MEMCACHE_* variables from these, or pass these values to your client when you create a new one in your code.

For example, pseudo-code for the first approach is:

env[MEMCACHE_SERVERS] = env[MEMCACHIER_SERVERS]
env[MEMCACHE_USERNAME] = env[MEMCACHIER_USERNAME]
env[MEMCACHE_PASSWORD] = env[MEMCACHIER_PASSWORD]

While pseudo-code for the second approach is:

memClient = new MemcacheClient(ENV['MEMCACHIER_SERVERS'],
                               ENV['MEMCACHIER_USERNAME'],
                               ENV['MEMCACHIER_PASSWORD'])

Please be careful that you have setup the your client in all locations. Many frameworks, such as Rails, use memcache in multiple ways and may require you to setup initialization properly in a few locations. Generally the first approach is preferred as it is global while the second approach is local to each initialization.

For example, with Ruby on Rails, you’ll need to setup cache_store, Rack::Cache and the session_store.

Support

All MemCachier support and runtime issues should be submitted via on of the Heroku Support channels. You can also reach us directly at support@memcachier.com. We encourage you to CC us on any urgent support tickets sent to Heroku.

Any non-support related issues or product feedback is welcome via email at: support@memcachier.com.

Any issues related to MemCachier service are reported at MemCachier Status.

Please also follow us on twitter, @memcachier, for status and product announcements.