How to write a load test script – Part 1

One of the hardest parts of running a load test for your Facebook application is simply figuring out what to test. Since we’ve been through this a few times, we’ve come up with some ideas and tips for  how to do this properly and efficiently so that you can build a load test script that effectively tests your app.

An interesting observation we made was how closely the process of creating a test script is to Richard Feynman’s famous algorithm for solving every problem that you could possibly imagine. So let’s look at the steps you’ll need to take:

Building your FriendRunner test script

Step 1: Write down all of the things your user can do in the app

This is the tedius part of the exercise. Make a list of all of the features available to a user while he uses your application. Sometimes it’s useful to clump several discrete user actions into a single logical action. For instance, a user may browse to an account information page in your app, modify his information, and then save that change. When deciding what gets into a load test, it’s often better to think of user actions at a more macro level.

Step 2: Think really hard about what the user typically does when using your app

Does you application have a  page where you discuss your Privacy Policy? If not, you probably should, but that isn’t the issue. The issue is that very few of your users are ever going to this page. Ones that do will go once, and never return. Serving this page will probably incur very little load on your server that fulfills the request. Ergo, looking at the Privacy Policy should not be a part of a load test. Seems kind of obvious when you see it written down, but we’ve seen many things like this in proposed scripts.

What you should be putting into your script are the “normal” things that your user does when he interacts with your application. You can figure out what this is by observing how users interact with similar services (e.g. if you’re already running a non-Facebook version of your web application) or with the liberal use of some common sense.

Step 3: Write down the list of things to do for your load test script

Here’s the easy part. Once you decide on what a normal user does when he interacts with your app, put the steps together in a reasonable order. If several steps have some type of dependency on each other, take this into account. It’s also important to consider whether one user’s actions will have consequences for another user.

Special handling of FriendRunner load test scripts

In our next post, we’ll discuss some cool FriendRunner features that will allow your test scripts to more closely approximate the real world. Things such as going to some pages for some users but not others, or changing the user behavior based on information that’s displayed on the pages shown.

Contest

Identify the company that’s represented on the t-shirt that Feynman wears in the above picture, and name one thing that he did for that company. First person to answer correctly will be named Alpha Geek, and have their name posted on this page. Send your responses to contest@friendrunner.com.

Winner

Dr. Saul Kravitz was the first one to identify Thinking Machines as the company represented on Richard Feynman’s shirt. Feynman worked there for several years doing everything from painting the walls to developing deep insights into parallel computation.

For more info about Feynman’s relationship with Thinking Machines, see http://www.longnow.org/essays/richard-feynman-connection-machine/ 

2 Comments

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  By Saul Kravitz, June 7, 2010 @ 7:40 am

  Thinking machines. http://www.longnow.org/essays/richard-feynman-connection-machine/

  Running Hopfield neural nets on the CM

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  By admin, June 8, 2010 @ 8:29 pm

  Correct!

  I was actually thinking that Feynman spent some time painting the walls at Thinking Machines, but that neural nets thing is acceptable too.

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