ApacheBench (ab) is "a tool for benchmarking your Apache Hypertext Transfer Protocol (HTTP) server." It is built in to most current versions of Mac OS X and Linux. It's a quick way of sending multiple requests to a website and timing how long they take.
Basic Test
At its most basic, ab can perform successive and/or concurrent load tests on a webpage. Run the following command in the Terminal (Mac OS X; if you don't have OS X, ab is installed on the corn cluster machines):
ab -n 30 -c 2 http://yoursite.stanford.edu/
(Remember to include a trailing slash after the URL or ab will return an error.)
This test hits the URL at yoursite.stanford.edu 30 times (-n 30) with a maximum concurrency of 2 simultaneous requests (-c 2).
You'll get a result like the following:
The Total row displays a summary of load time statistics; the mean column shows the average load time, in milliseconds, of all 30 requests. So the average load time in this test was 2.7 seconds (2724 ms), and the longest load time was 5.3 seconds (5376 ms).
Authenticated Test
If you want to test the load time of Drupal pages that are only available to certain logged-in users, you need to give ab a cookie. (Give the Cookie Monster a cookie too.)
First, log into the Drupal site as the user you want to run the test.
Then, in Firefox, go to the Privacy tab of the Firefox Preferences (Firefox->Preferences on Mac, Tools->Options on Windows), and click Show Cookies.
You may have to do some digging, but the cookie you're looking for will start with "SESS" and should be in the domain ".stanford.edu". You're looking for the Name and Content values.
Now, pass those cookie values to ab like so (copy and paste are your friends here):
ab -n 30 -c 2 -C SESS9e564fab3f27945d93518a08f274543f=d90c5738c81061df83 http://yoursite.stanford.edu/admin/user/permissions
This will give you an output like the following:
Troubleshooting
You can use the -v flag to set the verbosity level of ab. From the manpage:
-v verbosity Set verbosity level - 4 and above prints information on headers, 3 and above prints response codes (404, 200, etc.), 2 and above prints warnings and info.
So the command:
ab -v 4 -n 30 -c 2 http://yoursite.stanford.edu/
Will also return all the warnings, info, response codes, and headers that ab encounters on each run.
