Jmeter - when there are number of threads are running, the variable from JSON extractor is not working sometimes

Question

I am now using Jmeter to run the test of APIs.

The situation is that I have a login Api which will return a token inside response. I use a JSON extractor to save the token as a variable. Then, I use the ${token} is the header of other requests.

However, I found that when I was trying to run 40-50 threads, the ${token} in some threads would be empty, and caused a high error rate.

Therefore, may I ask is there any method to solve it and why?

Thanks very much.

Answer 1

Try saving full response from the Login API, most probably your server gets overloaded and cannot return the token and returning some error message instead.

There are following options:

1. If you're running JMeter in command-line non-GUI mode you can amend JMeter's Results File Configuration to store the results in XML form and include the response data, add the next lines to user.properties file:

    jmeter.save.saveservice.output_format=xml jmeter.save.saveservice.response_data=true

   and when you run your test next time the .jtl results file will contain response bodies for all the requests.

2. Another option is using a Listener like Simple Data Writer configured like:

   

   and when you run the test the responses.xml file will contain the response data

Both .jtl results file and responses.xml can be inspected using View Results Tree listener

More information: How to Save Response Data in JMeter