The team over at Promet Source is sharing their expertise in a webinar showing you how to properly stress test your Drupal site. Andy Kucharski has asked me to join him in sharing best practices with anyone needing to understand the load testing process.

Register for the webinar

Andy is a frequent speaker at Drupal camps and conferences all over the country. He is recognized as one of the top minds in the world when it comes to architecting an effective Drupal implementation. Andy's reputation recently has skyrocketed as the foremost performance specialist on Drupal technology.

Real Drupal Performance Data from Promet Load Tests

One of the coolest parts of the webinar will be Andy's data that compares the performance of Drupal hosted on Amazon versus Rackspace. His team has done some real load testing with Drupal identical applications installed on different environments. There are statistics for AWS EC2 Small and Medium instances, and there are stats for Rackspace Cloud 2G and 4G instances.

Stress tests are good for finding out how many people can be on your website at the same time. A good test plan for an e-tailing site includes scenarios that represent people browsing your product pages and searching for specific items. It should also have realistic traffic for buyers going through the shopping cart experience and purchasing products with a credit card.

I had a call yesterday from a customer that wanted to stress test his e-commerce site with about 100,000 concurrent users. He explained that their marketing department is expecting significant growth of their sales because of a combination of the economic outlook, increased advertising, and a cool new unique channel technology that is going into production.

Thanks to some data from Gallup, Experian, and Pew Research, Marketing Charts produced some great graphs that show how the U.S. economic financial growth indices are improving in the past year or so. Consumers are spending more online with e-tailing sites, perhaps because they are more confident that their financial situation is improving.

Online Spending is Healthy

In January, 58% of survey respondents said 2011 will be better than 2010, 20% said 2011 will be worse, and 21% said it will stay the same. As the mood has improved, so has online spending which hit a record of $43.4 billion in the fourth quarter of 2010. That's up from $32.1 billion in
Q3 2010, and it is the fifth consecutive quarter of positive year-over-year growth and second quarter of double-digit growth rates in the past year. So, online spending is one of the most vigorous parts of our economy right now. Is your site ready for growth?

Here are a few good insights about software performance from Robert Read in his eBook entitled, How to be a Programmer: A Short, Comprehensive, and Personal Summary. Robert dedicated the book to his colleagues at Hire.com.

My favorite parts are listed here as excerpts and included below in the original context:

• Bottlenecks in performance canl be an example of counting cows by counting legs and dividing by four instead of counting heads.
• The purpose of stress testing is to figure out where the wall is, and then figure out how to move the wall further out.
• If the wall is too close to satisfy your needs, figure out which resource is the bottleneck (there is usually a dominant one.) Is it memory, processor, I/O, network bandwidth, or data contention?
• Performance is a part of usability.
• Most software can be made (with relatively little effort) 10 to 100 times faster than they are at the time they are first released.
• If a well-isolated algorithm that uses a slightly fancy algorithm can decrease hardware cost or increase performance by a factor of two across an entire system, then it would be criminal not to consider it.
• A plan for stress testing should be developed early in the project, because it often helps to clarify exactly what is expected. Is two seconds for a web page request a miserable failure or a smashing success? Is 500 concurrent users enough?
• I've made errors such as failing to provide a relational database system with a proper index on a column I look up a lot, which probably made it at least 20 times slower.
• Other examples include doing unnecessary I/O in inner loops, leaving in debugging statements that are no longer needed, and unnecessary memory allocation.
• Stress testing is fun.
• Who has particular knowledge about a component also constantly changes and can have an order of magnitude effect on performance.
• Finding the expensive I/O and the expensive 10% of the code is a good first step
• There is not much sense in optimizing a function that accounts for only 1% of the computation time.
• Each change brings a test burden with it, so it is much better to have a few big changes.

Today I read an article by Omer Brandis on IT Toolbox about SAP stress testing versus performance testing. Maybe his perspective differs from mine because he is not focused on web applications. I just haven't seen other technologists use the definitions and goals of the two types of testing like Omer uses them.