Understanding VSTS Load Test Counters: Requests, Pages and Tests

Wednesday, February 18, 2009

Microsoft Visual Studio Team System/Test Edition provides an excellent tool to perform web site load testing. Using this load testing tool, you can monitor and measure the site performance along with system status with respect to a given load/stress.

Fortunately VSTS provides a support for wide range of performance counters, from web page request per second to condition of physical disk, memories. Unfortunately, they are too huge that, initially testers/designers get overwhelmed with all of those, to find out a clear idea about the performance of the site they built. Today we’ll be discussing about three counter sets that are closely related to each other, but provides a meaningful information about the health of the target web site to be load tested.

Definitions

Requests: Requests are the smallest load testing parameter with respect to a web page.

It contains details for individual requests issued during a load test. This includes all HTTP requests, and dependent requests such as images, css and java-script files.

Meaning, each refereeing contents in a web page, such as images, css files, java-script files will generate separate request along with the request for the web page which includes the actual textual content (text, tags etc). It will include the same number of additional entries for a postback.

Pages: Right after “Requests” we can consider “Pages” as the next level of load testing counter set, which is defined in MSDN as “Displays a list of pages accessed during a load test run. Some data in this table is available only after a load test has completed.”

For instance, we have a web page, which has a button, clicking on which shows a message on that page, which generate two entries for Page counter.

One important note is, any redirection to a separate page will not be counted with additional value, however the corresponding Requests for the redirected page will be counted.

Tests: Contains the details for individual tests run during a load test.

For instance, we have created a web test, that contains two web pages, pushing on a button on the first page will re-direct the user to the second page, although there will be multiple entries will be involved for Requests and Pages counters, but the whole process will be considered as a single Test.

Case Study

To have better idea, lets consider 4 different cases to see the corresponding entries with respect to the counters we are discussing.

Text only:

We have a web page, that contains only textual content, no external content such as image, css, java-script file referred there. However it may contain html controls, but no postback (button click etc) will be considered here.

Counter Status: number of request = number of pages = number of tests