Tips and Techniques for Using Apache JMeter for Load Testing

Apache JMeter is a great tool for load testing and we use it for LAN-based products as well as web sites and hosted services. And lately we've used it in conjunction with Amazon's Elastic Cloud Compute (EC2) service. Along the way, we've collected a number of tips and techniques that are sometime difficult to find in the documentation.


Here's a list of changes that we've found to be necessary each time we use jmeter:

Change Memory Settings
The default memory settings are too low need to be increased to the maximum memory available. To do this:

1. Navigate to jmeter/bin.
2. Edit jmeter (Linux command-line: "pico jmeter", Windows: open jmeter.bat with wordpad)
3. Scroll to the line that reads: HEAP="-Xms256m -Xmx256"
4. Change the numbers to meet your system specs (first number is the minimum, second maximum). For example: HEAP="-Xms1024m -Xmx1024"
5. Save changes.

Retries & Timeouts
If you are doing load testing with jmeter, inevitably you'll place enough of a load on your target server that it may have trouble responding. In order to give the server a chance to respond you may want to change the retries and timeout values. To do this, edit the jmeter.properties file for retries = 3 and timeout = 120. Be sure to delete the #s at the start of the lines or they will remain commented out.
--Note: The generic HTTP Request does NOT support these features, and the HTTP Request HTTP Client sampler type must be used.
--Note: The HTTP Request HTTP Client sampler does NOT support automatic redirect so be sure to deselect this (its checked by default) when creating the JMeter tests.

Ports (Windows only)
If you've ever seen this error message when running jmeter "JMeter Exception: java.net.BindException: Address already in use: connect" you've run out of ports. To avoid running out of available ports on Windows (and thus seeing a Address Already In Use error), there's a great explanation and solution posted on the twit88.com blog at this article.