Correlation in JMETER

                               Correlation in JMETER

This post is related JMeter. We will discuss correlation process/ method in Jmeter.

As I mentioned before, JMeter does not support automatic correlation. We use regular expression to performing correlation in JMeter.

Now let’s move to Correlation in JMETER.

What is correlation.

To capture a dynamic value from server response in performance testing is Correlation. It fetches dynamic values from earlier responses and supplies those values to subsequent requests.

Why we need correlation?

Most of the time, web application which has time based, user-based concept implemented, Server sends dynamic response basis of various factors like unique username password, OTP, time/date.

A dynamic response always returns with different data for each iterative request and may affect the subsequent requests. Correlation if implemented properly extracts the dynamic value from the response, store in a variable and use it in all required requests

Regular Expression Extractor

This is feature which used for correlation in JMETER. We can add "Regular Expression Extractor" using post processor section as below image

Let me explain each field name of this window

Reference Name: This is the name of the JMeter variable to store the result.

Regular Expression: The expression to parse the data from response.

Template: The template is an arbitrary string with special elements. These elements refer to groups within the regular expression. The syntax ‘$1$’ refer to group 1, ‘$2$’ refer to group 2, etc.

Match No.: The regular expression may come up with multiple matches. You can tell extractor which one to pick. Value Zero indicates that JMeter can choose any random match.

Default Value: If Regular Expression does not match any value, then the reference variable will pick default value. You can keep “Fail” or “Incorrect Token Value” message as default value.

Apply To: This field indicate samplers that can generate sub-samples, e.g. HTTP Sampler or samples generated by the Transaction Controller.

-Main sample and sub-samples: Apply to Main & Subsample both

-Main sample only: Only applies to the main sample

-Sub-samples only: Only applies to the sub-samples

-JMeter Variable: Assertion is to be applied to the contents of the named variable

Field to check: this says which part of response values should be searched using regex.

-Body: body of the response, e.g. the content of a web-page (excluding headers)

-Body (unescaped): body of the response, with all Html escape codes replaced. Note that Html escapes are processed without regard to context, so some incorrect substitutions may be made.

-Body as Document: extract e text from various type of documents via Apache Tika

-Response headers: Header of response in HTML pages

-Request headers: to look into request headers of html page

-URL: As name suggest, URL of Response

-Response code: As we know each response has standard code e.g. 200

-Response Message: like O.K. message in Response

Note: Body(unescaped) and Body as Document can impact performances so, use wisely

 See the example of one correlation, i have created to capture APP verify key:

Now see steps we should follow to do correlation using above template:

1. Run the test and try to identify the dynamic value in the in the View Results Tree.

Note:

Need to run for multiple times and compare the results manually.

 2.Identify the LB, RB of the dynamic value

 3. Write the regular expression for the dynamic value using the LB and RB. Check the regular expression using View Results Tree.

4. Find the occurrence (match number) for the required dynamic value

5. Add the regular expression extractor for the previous request.

Hopefully this post will give a picture on correlation process of Jmeter.

Happy Testing!!

To start with JMeter and Regular expression, you can go through my previous post on JMeter and Regex

1.       JMeter:Open Source Tool GUI

2.      JMeterThread Groups: Type of Thread groups

3.      JMeter:Thread Group Configuration 

4.      RegularExpression in Performance Testing

5.      Let’slearn Regular Expression 

6.      Let’slearn Regular Expression -2

7.      Let’slearn Regular Expression -3