Hammerhead is a new Firefox/Firebug add-on that allows for measuring the response time of a Web site using a real browser for a defined number of executions. It measures the Median and Average response times of both an empty and a primed cache. What is interesting about Hammerhead is that it uses a real browser and adds the ability to record response times from the browser for a given number of executions.

Hammerhead Firebug Plugin Measuring Page Performance within Firefox

Performance Testing with a Real versus Simulated Browser

The reason the response times will vary for the same request is because simulated tests are essentially opening a raw HTTP connection, along with headers, cookies and content encoding, receiving the response, and closing the stream (see HTTPSampler.java in the Jmeter source code for an example).

Hammerhead has a different approach in which it calls the underlying browser to do the work, and uses an iframe to measure when the iframe was to to the onload event. Thus including all of the parsing and rendering of JavaScript, CSS, DOM, and other API calls that happen when an URL is loaded on a browser.

Both methods valid ways of measurement Web performance, and both serve different purposes. For example: I would not be able to perform capacity testing using Hammerhead, because I would need hundreds or thousands of browser instances to accomplish this (feature request?), and isn’t doable on a single developer workstation; whereas with Jmeter, the ability to test hundreds or thousands of current connections is doable, provided I have the bandwidth and computing capacity to support such a load.

In Summary

Hammerhead is a useful and quick utility for performing real browser response time testing. I performed some simple tuning exercises and used Hammerhead to test the results in the browser and it was quick and efficient for getting fast readings on performance tweaks with the actual JavaScript and CSS as well as Web server performance options such as encoding, expires headers, and caching headers.

Further Reading

Steve Souder’s Hammerhead Blog Post http://www.stevesouders.com/blog/2008/09/30/hammerhead-moving-performance-testing-upstream/

Hammerhead Home http://stevesouders.com/hammerhead/