JMeter Tips: User Defined Variables

In my previous post I linked to some basic JMeter test plans, as I was just getting comfortable with JMeter. Sine then, I've found a way to make the scripts more maintainable by using user defined variables. Here's the link to a simple script that uses variables.

The syntax for referencing a variable in JMeter is ${VARIABLE_NAME}.

What I like to do is add a user defined variables config element to the top of the test plan and put all the settings in there I'd like to tweak. For example, URL's, timeouts, etc. All in one place at the top of the script. This makes it easy to tune scripts, e.g. to test different pages, to tweak the number of users, etc.

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Basic Web Performance Testing With JMeter and Gatling

Introduction In this post I'll give a quick way to get some basic web performance metrics using both JMeter and Gatling.

JMeter is a well known, open source, Java based tool for performance testing. It has a lot of features, and can be a little confusing at first. Scripts (aka Test Plans), are XML documents, edited using the JMeter GUI. There are lots of options, supports a wide variety of protocols, and produces some OK looking graphs and reports.

Gatling is a lesser known tool, but I really like it. It's a Scala based tool, with scripts written in a nice DSL. While the scripts require some basic Scala, they are fairly easy to understand and modify. The output is a nice looking, interactive, HTML page.
Metrics Below are the basic metrics gathered by both JMeter and Gatling. If you are just starting performance testing, these might be a good starting point.

Response Time – Difference between time when request was sent and time when response has been fully received

Latency –…

Multi Threaded NUnit Tests

Recently I needed to reproduce an Entity Framework deadlock issue. The test needed to run in NUnit, and involved firing off two separate threads. The trouble is that in NUnit, exceptions in threads terminate the parent thread without failing the test.

For example, here's a test that starts two threads: the first thread simply logs to the console, while the other thread turfs an exception. What I expected was that this test should fail. However, the test actually passes.

readonly ThreadStart[] delegates = { () => { Console.WriteLine("Nothing to see here"); }, () => { throw new InvalidOperationException("Blow up"); } }; [Test] public void SimpleMultiThreading() { var threads = delegates.Select(d => new Thread(d)).ToList(); foreach (var t in threads) { t.Start(); } foreach (var t in threads) { t.Join(); } }
Peter Provost posted an article that describes how to make this test fail. It works…

Generating Java Mixed Mode Flame Graphs

Overview I've seen Brendan Gregg's talk on generating mixed-mode flame graphs and I wanted to reproduce those flamegraphs for myself. Setting up the tools is a little bit of work, so I wanted to capture those steps. Check out the Java in Flames post on the Netflix blog for more information.

I've created github repo (github.com/jerometerry/perf) that contains the scripts used to get this going, including a Vagrantfile, and JMeter Test Plan.

Here's a flame graph I generated while applying load (via JMeter) to the basic arithmetic Tomcat sample application. All the green stacks are Java code, red stacks are kernel code, and yellow stacks are C++ code. The big green pile on the right is all the Tomcat Java code that's being run.

Tools Here's the technologies I used (I'm writing this on a Mac).
VirtualBox 5.1.12Vagrant 1.9.1bento/ubuntu-16.04 (kernel 4.4.0-38)Tomcat 7.0.68JMeter 3.1OpenJDK 8 1.8.111linux-tools-4.4.0-38linux-tools-commonBrendan Gregg's Fla…

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