What is correlation?

I trust you have followed my earlier posts on this blog to get yourself started on LoadRunner. If not you can find them here

Ok, so now we come to one of the most important topics in LoadRunner — Correlation. I would recommend you to understand each and every aspect around this topic.

If you simply record and playback a script in VuGen, you might encounter errors in your playback. Often, those errors are related to the session values which are sent by the server to the client to identify that particular session.

Why error? Well, session values will change with every playback of the script.

To overcome this we need a way which can capture these dynamically generated session values and pass it subsequently to any part of the script, wherever required. This method to identify and set the dynamic generated value is known as correlation.

If your new to loadtesting, don’t confuse this term with parameter which you might have used in tools like QTP to pass varying values. Parameter is not a dynamic value captured from server response but it is something for which the user has predefined data values available.

LoadRunner use three functions to correlate scripts:

  1. Web_reg_save_param
  2. Web_create_html_param
  3. Web_create_html_param_ex

The last two are just used for backward compatibility. The first function is used often. We will touch upon details of this function in the next post


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