What is correlation? Explain types of Correlation.

Correlation is a process to capture dynamic values and pass them at appropriate places in the script on run time.

E.g. There are situations when a request is based on a response of previous request received from the server, such as, a Session ID, server date/time which is fetched from server. Depending upon the configuration of the servers, these values changes (it might change every time you run the application, after certain time, hour, day etc.). Obviously, if the execution of script depends upon a value returned by server, it means we need to find a way where we can “catch” the server response and replace those values in the requests where it is required. This whole process is called Correlation in Loadrunner.

In simple words, the solution by using Correlation is:

1. Capture response of previous step

2. Use captured value of step 1 to serve as input to all subsequent steps

Loadrunner provides 2 ways for doing correlation.

1.       Automatic Correlation

Loadrunner has provided a mechanism by which we it will automatically capture the dynamic values.

Below are the steps for Automatic correlation

I.            Open Recording options by clicking Record à Recording options (Ctrl + F7)

            

            II.      Below window will open

                

        III.            Check following check boxes

a.       Rules Scan

b.      Automatically correlate values found – If you check this option then vugen will not ask for correlation, it will automatically correlate the dynamic values for the defined rules.

c.       Record Scan

d.      Replay Scan

                IV.            Click on Rules (Correlation à Rules)

In this window you can choose the application you are recording. Loadrunner has provided some predefined rules for various applications.

You can create new rules for your application if you know left and right boundaries. We will take this topic in my next article.

                  V.           Click Ok. If you have already recorded the application then click on regenerate the script. It will replace all the dynamic values which are identified by defined rules.

Note. We can do the same process of automatic correlation before recording the script, then we don’t need to regenerate the script.

2.       Manual Correlation

In this we directly identify the dynamic value and write code in the script

Below are the steps for doing manual correlation:

                    I.            Find the dynamic value which is required to correlate.

                  II.            Find unique left and right boundaries of where dynamic value is coming from the server.

                III.            If unique left and right boundaries can’t be found then find for which occurrence of left and right boundary this dynamic value is coming.

                IV.            Add a web_reg_save_param function to the script, above the request whose response contains that dynamic value.

                  V.            Add a parameter name, left boundary, right boundary, and occurrence to the function

                VI.            Replace the dynamic value with this parameter in the script every time it occurs.