eZ Publish Performance Optimization Part 1 of 3: Introduction and Benchmarking

In order to make performance improvements, you need to first identify the performance capabilities of your system.

Benchmarking

ApacheBench ("ab"), http_load and siege are three useful benchmarking tools that are run from the client or server command line to test webserver performance. Selenium IDE is a benchmarking tool that runs in a browser, described in a previous article about Selenium.

In this article, we will outline the usage of ab, siege and http_load. These tools can be run on both the server or the client. Running the tools on the client can help to identify network delays, while running the tools on the server will eliminate such delays from the test results.

Our example tests in this article will use two parameters: concurrency and number of requests. "Hammering" is the term used to described repeated requests during testing. It is important to know the type of architecture you are running on the server when choosing concurrency levels.

For example, a Pentium 4 CPU uses hyperthreading technology, which enables it to run two processes in parallel. This means that two concurrent requests are almost twice as fast as one request. If you have a server with more than one P4 CPU, you would multiply the number of CPUs by two. In our case we used dual Xeon servers and ran a concurrency of 4 or more to get the maximum performance from the server.

At the most basic level, we are interested in discovering the page generation and transfer times of different pages. This is usually expressed in pageviews per second or other similar results such as percentage of requests served within a certain time.

Monitoring tools

When you are running benchmarking tests, it is useful to use a monitoring tool such as top or vmstat to display continuous information about server parameters.

Check that the load on the I/O (that is, transfer to and from the CPU and memory core) is not limiting performance. When benchmarking an eZ Publish site that is properly configured, you should be limited by the CPU and not the I/O. You should see close to 100% CPU usage when hammering the server. If the I/O shows a high load, this might indicate that you are out of memory, and that the memory is being swapped to the hard drive. Ideally the load should be steady at approximately 1-2, which means that there are only one or two processes waiting for the CPU.

If your application uses the MySQL database heavily, you should monitor the health of MySQL while doing hammering. You can use mtop to monitor what MySQL is doing and identify slow queries.

We will not detail the top, vmstat and mtop commands in this article, but you can find information about them on their respective webpages or by running the "man" command.