What Is Correlation in VUGen Scripting?


Larry Thompson

Correlation is a fundamental concept in VUGen scripting that plays a key role in performance testing. In this article, we will explore what correlation is and how it can be applied effectively in your VUGen scripts.

Understanding Correlation

Correlation refers to the process of capturing dynamic data and replacing it with a parameter or variable in your script. In performance testing, dynamic data often includes session IDs, timestamps, user-specific data, and other unique values that change with each iteration.

Why is Correlation important?

In order to simulate realistic user behavior during load testing, it is essential to capture and replay these dynamic values accurately. Without proper correlation, your script may fail to mimic real-world scenarios, leading to inaccurate test results.

The Correlation Process

The correlation process involves the following steps:

1. Identify the dynamic values: Start by identifying the dynamic values that need to be correlated. These are typically found in server responses or requests sent by the client.

2. Find the right correlation function: Once you’ve identified the dynamic values, you need to determine the appropriate correlation function to use. VUGen provides several built-in correlation functions such as web_reg_save_param and web_reg_save_param_ex which can be used depending on the type of data you are trying to capture.

3. Create a parameter: After selecting the appropriate correlation function, you need to create a parameter or variable that will hold the captured value. This parameter will later be used to replace the dynamically generated value during script execution.

4. Capture and replace: With the parameter in place, you can now capture the dynamic value using the selected correlation function and replace it with the parameter using its corresponding name. This ensures that each iteration of your script uses a unique value for these dynamic parameters.

Types of Correlation

There are various types of correlation techniques that can be used in VUGen scripting, including:

  • Auto Correlation: This technique involves using VUGen’s automatic correlation feature to scan the script and automatically identify dynamic values. While this can be a time-saving approach, it may not always capture all the necessary dynamic data.
  • Manual Correlation: Manual correlation requires manually identifying and capturing the dynamic values using the appropriate correlation functions.

    Although it requires more effort, manual correlation provides greater control and accuracy in capturing the desired data.

  • Parameterization: Parameterization is a type of correlation where you replace static values in your script with parameters. This allows you to easily modify input data for each iteration, making your test more realistic and versatile.

Tips for Effective Correlation

To ensure effective correlation in your VUGen scripts, consider the following tips:

  • Analyze server responses: Carefully analyze server responses to identify any dynamic values that need to be captured. Look for patterns or unique identifiers that can help you locate these values.
  • Use regular expressions: Regular expressions can be powerful tools when capturing dynamic data.

    They allow you to define flexible patterns that can match various forms of the same value.

  • Verify captured data: After capturing dynamic values and replacing them with parameters, it is important to verify that the substitution was successful. Run your script with multiple iterations and check if each iteration uses a different value for the correlated parameter.
  • Maintain script efficiency: While correlating multiple values is essential, be mindful of script efficiency. Correlate only the necessary values to avoid unnecessary overhead and maintain optimal performance.


Correlation is a crucial aspect of VUGen scripting that allows you to accurately simulate real-world scenarios during performance testing. By effectively capturing and replacing dynamic data, you can ensure that your scripts behave like real users, providing accurate test results.

Remember to identify the dynamic values, select the appropriate correlation function, create parameters, and capture and replace the dynamic data. By following these steps and utilizing various correlation techniques, you can enhance the realism and accuracy of your VUGen scripts.

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