Distributed Coherent EhCache In less than 5 Minutes...

Need a fast clustered/persistent cache? Ehcache, the ubiquitous cache built into Spring, JBoss and Grails can be configured to provide those features in under 5 minutes using this brief tutorial.

A Brief Digression Into The Why

Why do I need a persistent scaled out cache? The main use cases for a clustered/persistent cache are:

• I'm using hibernate and it's pounding the database or it's too slow. Use a coherent second level cache to deflect load off the database, reduce latency without getting stale data.
• Have a bunch of intermediate data that doesn't belong in the database and/or is expensive to store in the database that I want to keep in memory. Problem is if a node goes down or if someone asks for the data from another node the data is lost
• I'm already caching but I have to load data over and over again into every node even though hot data for one node is hot for all (Known as the 1/n effect). If the data is cached for one node it is cached for all.

Steps:

1) Download the latest Ehcache www.ehcache.org

2) Put the following jars in your class path (all included in the ehcache kit):

ehcache-core.jar - Core Ehcache

ehcache-terracotta.jar - Terracotta clustering

slf4j-api-1.5.8.jar - Logging API Used by Ehcache

slf4j-jdk14-1.5.8.jar - Implementation of the Logging API

3) whip up some cache code:

 package org.sharrissf.samples;

import net.sf.ehcache.Cache;
import net.sf.ehcache.CacheManager;
import net.sf.ehcache.Element;

public class MyFirstEhcacheSample {
 CacheManager cacheManager = new CacheManager("src/ehcache.xml");

 public MyFirstEhcacheSample() {
      Cache cache = cacheManager.getCache("testCache");
      int cacheSize = cache.getKeys().size();
      cache.put(new Element("" + cacheSize, cacheSize));
      for (Object key : cache.getKeys()) {
           System.out.println("Key:" + key);
      }
 }

 public static void main(String[] args) throws Exception {
      new MyFirstEhcacheSample();
 }
}

4) Whip up some quick config

 <?xml version="1.0" encoding="UTF-8"?>

<ehcache xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
 xsi:noNamespaceSchemaLocation="ehcache.xsd">

 <terracottaConfig url="localhost:9510" />

 <defaultCache />

 <cache name="testCache" eternal="true">
                <terracotta clustered="true"/>
 </cache>

</ehcache>

5) Download Terracotta

6) Start the terracotta server in the bin directory with the start ./start-tc-server.sh

Now just run that Java snippet a few times and see your cache grow.