Apache Cookbook, 2nd Edition

11.2. Benchmarking Apache with ab

Problem

You want to benchmark changes that you are making to verify that they are in fact making a difference in performance.

Solution

Use ab (Apache bench), which you will find in the bin directory of your Apache installation:

ab -n 1000 -c 10 http://www.example.com/test.html

Discussion

Apache bench is a command-line utility that comes with Apache and lets you do very basic performance testing of your server. It is especially useful for making small changes to your configuration and testing server performance before and after the change.

The arguments given in the previous example tell ab to request the resource http://www.example.com/test.html 1000 times (-n 1000 indicates the number of requests) and to make these requests 10 at a time (-c 10 indicates the concurrency level).

Other arguments that may be specified can be seen by running ab with the -h flag. Of particular interest is the -k flag, which enables keepalive mode. See the following keepalive recipe for additional details on this matter.

There are a few things to note about ab when using it to evaluate performance.

Apache bench does not mimic Web site usage by real people. It requests the same resource repeatedly to test the performance of that one thing. For example, you may use ab to test the performance of a particular CGI program, before and after a performance-related change was made to it. Or you may use it to measure the impact of turning on .htaccess files, or content negotiation, for a ...