Tuesday, May 18, 2010

Steve Jobs Stanford Commencement

Was reading a couple stories on the web this morning and I ran into two somewhat interesting lists over at Time Magazine. I kinda mocked the first one upon reading the title "Top 10 College Dropouts." I laughed and said to my Coworker and friend Orion, "Must be a slow news day!" Followed by spending the next 10 or 15 minutes dissecting the article. How many were either from or lived in California? how many dropped out of Harvard? Who the heck is Buckminster Fuller? "About 10 minutes in Orion rightly pointed out, "Article can't be too bad since you've spent the last 10 minutes talking about it." Of course he was right.

Followed that up by clicking a link taking me to the next list called "Top 10 Commencement Speeches." I know what your thinking now, "How much free time does this guy have?" I was enjoying a little candy after a hard working morning ;-). Anyway, I digress. I noticed that one of the names was on both lists. You guessed it, Steve Jobs, someone that anyone who has ever built anything of any kind should at least respect.

I set about to watch the commencement speech he gave in 2005. He basically tells 3 stories from his life experience. Much like Randy Pausch's last lecture their is a lot to be learned here. The first two stories are awesome and inspirational and many of us can relate to and learn from them. The third is also good/inspirational but a bit dark and kind of scary and depressing.

Anyway, since in this speech Steve talks so much about time, I will lead in with the opinion that listening to this commencement is time well spent. Check it out!

Friday, May 07, 2010

A Couple Minutes With Non-Stop Ehcache

Sometimes you just want to have an SLA (Service Level Agreement) when dealing with a component like a cache. You want to know that no matter what goes wrong, disk failures, deadlocks, network down, database locked up (for write-through) your threads won't be blocked for longer than your SLA. In the security world this is analogous to Layered Security where one is protected at multiple layers from breaches. In this case you are protected at multiple layers from hangs.

Non-Stop Ehcache

In comes NonStopCache. This is a decorator for Ehcache that allows one to specify an SLA. When using this decorator no operation is allowed to take longer than the SLA provided. All operations are isolated from the cache via a thread pool providing complete protection. The NonStopCache has multiple ways of configuring it. One can setup whether to serve stale data, perform noops or throw exceptions when SLA's are being violated covering most of the cases one needs.

Getting Started

Here's what I did to get started using clustered Ehcache and NonStopCache:

  • run the below program (source code below)
java -cp .:ehcache-core-2.1.0-beta.jar:slf4j-api-1.5.8.jar:slf4j-jdk14-1.5.8.jar:ehcache-terracotta-2.1.0-beta.jar:ehcache-nonstopcache-1.0.0-beta.jar MyFirstNonStopEhcacheSample

NOTE: Kill the Terracotta server when the printed output instructs you too.

Let's review the output:

Regular cache. No Decorator
The size of the cache is: 0
After put the size is: 1
Here are the keys:
Done with cache.

Sleeping, Stop your server
Disconnected NonStop with noop cache.
The size of the cache is: 0
After put the size is: 0
Here are the keys:
Done with cache.

Disconnected NonStop with local reads cache.
The size of the cache is: 1
After put the size is: 1
Here are the keys:
Done with cache.

Disconnected NonStop with exception cache.
Exception in thread "main" net.sf.ehcache.constructs.nonstop.NonStopCacheException: getKeys timed out
at net.sf.ehcache.constructs.nonstop.behavior.ExceptionOnTimeoutBehavior.getKeys(ExceptionOnTimeoutBehavior.java:114)
at net.sf.ehcache.constructs.nonstop.behavior.ClusterOfflineBehavior.getKeys(ClusterOfflineBehavior.java:120)
at net.sf.ehcache.constructs.nonstop.NonStopCache.getKeys(NonStopCache.java:264)
at MyFirstNonStopEhcacheSample.addToCacheAndPrint(MyFirstNonStopEhcacheSample.java:45)
at MyFirstNonStopEhcacheSample.(MyFirstNonStopEhcacheSample.java:40)
at MyFirstNonStopEhcacheSample.main(MyFirstNonStopEhcacheSample.java:60)

What Just Happened?

The cache is first loaded into an ordinary undecorated cache. This is performed before the server kill and proceeds without incident. The next round of operations on the cache were performed with the server down.

Since that cache is configured as noop all operations are ignored and the size of the cache appears as zero. This is great for when you just want to not bother with the caching if it isn't available.

Next round is local reads. This allows you to use the values that are available locally while the cache is unavailable. This is especially nice for read only or mostly read only caches that fit in memory and are always available.

After that we go to the exception version. If you have a cache of important coherent data but you don't want threads blocked this setting is for you. It will blow cache operations out of the thread so your container can just keep going by either showing an error page or getting the data from elsewhere.

Some interesting points here:
  • These decorators are all being used on the same cache. This way you can make the behavior specific to the user of the cache. It gives tremendous flexibility.
  • You'll notice this little sample flies through despite the timeout being set to 13 seconds. This is because it's in fail fast mode. In this configurable mode if the cache knows it can't communicate it will return the failure case immediately. If that's not what you want you can instead set it up to not fail fast and wait the full timeout no matter what.
  • I did this work in config but the same setup can be done in code
The Code


And the Config file ehcachenonstop.xml:

Saturday, May 01, 2010

A Couple Minutes With Terracotta Toolkit Nightly

A couple days ago I wrote a short blog about our goal of creating a Terracotta Toolkit for others to easily build simple to use scaled out frameworks, tools and in some cases apps. This same exact toolkit is used to build Ehcache, Hibernate, Http Sessions and Quartz with Scale and HA just by adding 2 lines of config. I was pretty shocked and excited about what a tremendous reaction this blog and the toolkit received. Usually when I write a blog most of it's traffic comes from awesome sites like DZone but this blog was different. I actually got considerably more direct traffic from things like e-mails and twitter than anything conventional. That kind of viral excitement shows a much deeper level of curiosity and is tremendously motivating for the team here. Anyway, I digress.

Me being the curious type I decided to do something a little dangerous yesterday. I asked Geert, one of the leads on the Terracotta toolkit project, if we were in a state where I could play around with it a bit and get a sense of how hard it is to get started. We discussed the usual caveats, "We haven't agreed on some of the naming and factoring stuff yet?" which I clearly understood. Knowing that fact and that I'd be working off a nightly(this link downloads it) I set out to follow his simple instructions and see just how easy it was. Here is what I did.

Geert gave me a simple cyclic barrier sample to work off of. This is a sample I've whipped up my self a few times over the years. Many of our earliest users leveraged Terracotta strictly as a distributed lock manager and that's what this simple sample does as well. You start the app with a barrier name and a node count and it just hangs until the node count is reached. Seems like as good of a sample as any to highlight how to get started with the toolkit.

tar -xzvf terracotta-trunk-nightly-rev15534.tar.gz

  • Grabbed a quick sample app

import org.terracotta.api.ClusteringToolkit;

import org.terracotta.api.TerracottaClient;

import org.terracotta.coordination.Barrier;

public class PlayingWithExpressBarrier {

public static void main(String[] args) {

final String barrierName = args[0];

final int numberOfParties = Integer.parseInt(args[1]);

//Start the Terracotta client

ClusteringToolkit clustering = new TerracottaClient(


//Get an instance of a barrier by name

Barrier barrier = clustering.getBarrier(barrierName,


try {

System.out.println("Waiting ...");

int index = barrier.await();

System.out.println("... finished " + index);

} catch (Exception e) {





  • I worked in eclipse so at this point all I had to do is add the toolkit jar to the classpath to get it to compile

  • Now kickoff the Terracotta server

  • And run the sample 3 time
java -cp .:terracotta-toolkit-1.0-runtime-1.0.0-SNAPSHOT.jar barrierName 3

The first two nodes should hang waiting for the 3rd node. Once the 3rd node is started all three should run to completion. This is just a little taste of what is coming.

The toolkit will have highly concurrent maps, locks, counters, queues, evictors and more so stay tuned. All of the toolkit classes will have tests in our TCK. The toolkit will run on any 1.5/1.6 JVM and requires no boot-jars, agents or container specific code. Given versions of the TCK will allow people to just drop in that toolkit jar at runtime for any app developed using that version of the API provided by the version of the TCK. I'll talk a bit more about how versioning the toolkit API will work in a future blog but it will work like any other spec. You can use any implementation that implements the spec. Enjoy, much more to come.