5 Hints You're Using A Map When You Should Be Using a Cache?

When developing software in Java one almost always ends up with a few maps that contain keyed data. Whether it's username -> conversational state, state code -> full state name, or cached data from a database. At what point do you move from a basic Map (or one of it's more fancy variants like LinkedHashMap subclasses or ConcurrentHashMap) to an open source, light weight cache like Ehcache?

Here are 5 quick things to look for:

5) You've built your own Map loader framework for bootstrapping and/or reads triggering loading

4) You need to be able to visualize and/or control your Map via JMX or a console. For example you want to watch the hit rate of your Map or track the size of your Map.

3) You're hacking in "overflow to disk" functionality and or persistence for your Map in order to handle memory pressure and/or restartability.

2) You're hacking in special behavior to cluster Maps when you scale out. This includes things like writing your own invalidation and/or replication solution over jms or RMI

1) You find yourself implementing your own eviction strategies.

Avoid The Slippery Slope:

It's a slippery slope. First you add in one feature, then another, and next thing you know you've reinvented the cache wheel. No point in doing that. There are great caches out there that are apache licensed, light weight and have the above features you need and more.

To learn more about Ehcache check it out at ehcache.org »

Excellent Blog On Code Smells...

This is a really good/short blog that highlights some code smells that everyone should look out for. It's not a complete diary or anything but when I read it I felt like it could have been written by me.

8 Signs Your Code Sucks...

He also has a follow on which I agree with.

Comments are a sign of bad code and I am not sorry for saying it

Improved Web Browsing By Controlling Flash

I have a few pet annoyances when surfing the web.

* I find it disruptive to have audio play when I hit a web page (though I usually keep my sound off)

* I don't like when video plays automatically when I hit a web page.
* I don't like when my computer heats up and the battery drains when I'm not doing anything just because
I left a web page/tab open.

* Some pages that look rather slim take a disproportionately long time to load (there are lots of reasons for this but flash seems to be one of them)

Turns out that I was able to mostly solve those problems by using one of the many flash control
plugins. I surf on Safari for the most part so I went with ClickToFlash. FireFox has FlashBlock which I haven't tried.

The way it works is it shows you frames where flash usually should be. If you want to see what is there then just click on the box and it loads the real flash. It has many other nice features around content but the important one is the one I described.

I have to say, when I installed this thing I was absolutely amazed by how many things that looked like regular adds and images were actually flash. You will be astounded. Gotta wonder what these companies are doing with flash when they are showing a static image? I didn't take any official benchmarks but after installing I noticed an increase in battery life and decrease in heat on my computer. This experience makes me actually believe (didn't really at first) Apple's battery/cpu excuse for not supporting flash on the iPhone.

If your like me and only want flash when you want flash. Try it out.

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.