From Performance to Scale - A Software Story... Part I

When building most applications whether it's JEE, Spring, Grails or plain old Tomcat their are a series of common tools that are used. HttpsSessions is used for managing the state of the web portion, ORM for talking to a database, a cache to hold interimediate application state and a scheduler to make things happen at a certain time, place or interval. Out of the box it is quite easy to get started with these components. However, as an application makes it's way into production it often needs improved performance, often followed by HA and then scale-out.

This blog is about a journey. It's about taking an application from performance all the way to scale-out without rewrites and using the components that you already have.

In the beginning it's just the Application

The good news is that whether you're a JBoss person, a Spring person, a Grails person or a Tomcat person your really using the same key components. Almost everyone in these environments are using Hibernate as an ORM, the Http Session Spec, Ehcache for caching/performance and Quartz for scheduling. So while their is no official standard, the global consensus is pretty clear. If it's me I would start from Grails (which is built on Spring, Ehcache, Quartz and Hibernate) but doesn't require the 2 weeks of picking, deeply understanding and piecing together components that is required with most other approaches.

Round 1, Performance

So you've written your single node application using the usual components. Turns out, it's slow. Now what? Well the first thing you need to do is understand why it's slow at a high level. I usually check the following obvious things:

1) CPU bound - Check machines CPU stats on all nodes (including DB), now day you also need to figure out if one of your CPU's is maxed out which could mean the app needs more parallelism

2) GC Bound - Use verbose GC or your favorite tool

3) Database bottleneck - A number of tools and tricks exist to see if your database is the bottleneck. My favorite ways are:

- Keep track of and monitor query times and or look at hibernate stats

- Take thread dumps. If all threads are blocked on DB calls something is wrong

- Check resource Utilization on the Database machine

4) I also like to isolate operations and see which ones are slow or create slowness. This can tell you a lot about where to focus.

Ok, so now you know why things are slow and your in the same boat as about 90 percent of the world. The Database is the number one bottleneck.

Tuning the ORM

Many start by generating the ORM schema using tools. This usually ends up being a completely Normalized database that requires expensive queries. At this stage of development it's almost certain that this is where your performance problems will be. Aside from the usual mistakes like missing JDBC connection pool or bad JDBC Connection pool (Use C3PO and make sure your seeing parallelism. Many of the others are either useless or broken). The next thing to do is to try hibernate 2nd level caching. If your application is read heavy this can have an amazing impact on performance. Entity caching is generally the way to start. The most common gotcha is it getting invalidated by custom SQL. It is a little known fact that if you execute custom sql through hibernate it clears the cache making it useless. If you are going to do Query caching you MUST READ THIS BLOG.

Now you've got hibernate 2nd level caching turned on and you've tuned it. The database isn't the bottleneck anymore but your seeing a lot of GC and thread dumps show contention on Hibernate itself. Especially when displaying medium size to large tables of data on the screen.

Plus, it turns out that updating the database on every intermediate operation that occurs is pounding the databases locks, cpu and disk. It's also made my schema really unwieldy What do I do now?

Stepping up to Caching

If after 2nd level caching you still have performance problems it is usually time to look at application level caching. This can be extremely helpful for performance. If your seeing:

a) A lot of garbage creation around calculating results

b) cpu usage or contention getting information

c) Latency from IO in retrieving information from disk, a web service or a DB

d) Pounding your database with fine grained updates/information with information that you only needed for a short time.

You'll likely want to start caching. Some things to cache include:

1) heavily used reference data from the database - States, zipcodes, product ID's etc

2) Intermediate state - If a series of operations occur but all you care about is the end result. Cache until the end result is reached then put in the DB.

3) heavily reused calculated values - "Like totally searching for Britney Spears."

4) Temporary values that are only needed for a set amount of time - user sessions or data that is needed at a certain time of day.

Hopefully between the Hibernate caching and tuning and the Application data caching you've now got much of your performance issues under control.

Your application probably does some scheduling and uses http sessions but these rarely create performance problems in one node.

Part II - Now that it's performaning what about availability?

Part III - One node isn't enough anymore I need scale-out

Clustered Quartz Scheduler In 5 Minutes

Need a fast clustered/persistent Quartz Job Scheduler? Quartz Scheduler, the ubiquitous job scheduler built into Spring, JBoss and Grails can be configured to provide those features in under 5 minutes in this brief tutorial.

A Brief Digression Into The Why

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

• HA - You need to be able to restart your application without losing scheduled jobs
• Scale Out - Your application now needs more than one node to handle the load it receives and you want your scheduled jobs to distribute across nodes.
• You are using a database to persist and or scale your scheduler and you are seeing DB load/locking issues and or you find it two difficult to setup or maintain.

Steps:

1) Download Terracotta 3.2 (Which includes Quartz Scheduler) http://www.terracotta.org/dl/oss-download-catalog

2) Put the following jars in your class path (all included in the quartz-1.7.0 directory of the Terracotta kit from above):

quartz-1.7.0.jar - regular quartz jar
quartz-terracotta-1.0.0.jar - Terracotta clustered store

3) Whip up some scheduler code:

 public class QuartzSample {

public void startJobs() throws Exception {
  Properties props = new Properties();
  props.load(QuartzSample.class.getClassLoader().getResourceAsStream("org/quartz/quartz.properties"));


  // **** Begin Required TC props
  props.setProperty(StdSchedulerFactory.PROP_JOB_STORE_CLASS,"org.terracotta.quartz.TerracottaJobStore");
  props.setProperty("org.quartz.jobStore.tcConfigUrl", "localhost:9510");
  // *** End Required Terrocotta Stuff


  StdSchedulerFactory factory = new StdSchedulerFactory(props);
  Scheduler scheduler = factory.getScheduler();
  scheduler.start();
  if (scheduler.getJobDetail("myJob", "myGroup") == null) {
    System.out.println("Scheduling Job!");
    JobDetail jobDetail = new JobDetail("myJob", "myGroup", DumbJob.class);
    Trigger trigger = TriggerUtils.makeSecondlyTrigger(5);
    trigger.setName("myTrigger");
    scheduler.scheduleJob(jobDetail, trigger);
  } else {
    System.out.println("Job Already Scheduled!");
  }
}

public static class DumbJob implements Job {

  @Override
  public void execute(JobExecutionContext arg0) throws JobExecutionException {
    System.out.println("Works baby");
  }

}

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

** NOTE: Notice the two lines of properties that set things up for clustering with Terracotta in the sample. That's the only difference from single node unclustered Quartz.

4) Start the Terracotta server by running start

./start-tc-server.sh

in the bin directory of the Terracotta kit

5) Run the sample code above and watch it run the job every 5 seconds. Then kill the sample app and restart it. The app will tell you that the job is already scheduled and the job will continue.

Conclusion

Two lines of configuration and a server takes you from ubiquitous job scheduler built into Spring, JBoss and Grails to scale out and persistence.

Have fun!

Welcome James House and The Quartz Community

I'm excited to be welcoming James House and Quartz to the Terracotta and Ehcache Fold. The Terracotta dev and field teams have long believed that scheduling and coordination are hugely important parts of applications from single node to scaled out architecture. In Java that leads you to one place. Quartz! We believe James and Quartz are an excellent fit with our community and suite of products that are useful from single node to the cloud.

Quartz Scheduler is both a best of bread and a ubiquitous product. We are getting right to work on contributing. The first step along the path is the Mavenization and Hudsonifaction of the Quartz project which has already been completed! We also are ready with a beta version of Quartz Terracotta Express edition. It's an HA/Durability/scale-out version of Quartz that requires no DB and is so simple it can be leveraged in minutes by existing Quartz users. We look forward to working with James to create the most usable and useful enterprise class open source scheduler available and the enterprise class support product to go with it. We have lots of great feature ideas and we look forward to the journey ahead.

What To Do If Your iTunes Gets iHacked...

Please make sure you watch your iTunes receipts/charges. In the last week or so someone somehow started using my iTunes account to purchase music illegally. Yep, I got iHACKED! Fortunately I only got 2 bills worth around 75 bucks but if I hadn't been paying attention it could have been much worse. So make sure you read those statements!

If this happens to you immediately change your password and remove your credit card information from the iTunes site/app. You do this by:

1. Clicking on the store menu while in iTunes and then selecting the "View my account" menu item. From there click "Edit" on the main screen where it says "Payment Information" and select credit card type "None".
2. Next change your password. In the same "View My Account" screen click "Edit Account Info." That will take you to a screen where you can change your password.

Ok, now that you've protected yourself you need to get your money back. Unlike Amazon or Zappos contacting support and reporting the fraud DOES NOT lead to a refund. They will direct you to your credit card company to refute the charge. I did this and it appears to be successful (I found it disappointing that Apple didn't just take care of this for me).

As a side note, when shopping online make sure you have a credit card company that takes responsibility for stuff. Amex has always been great and I'm sure other good companies exist as well.

UPDATE:

Looks like I'm not alone here. This blog reads like I could have written it.

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.