JMeter Interview Questions and Answers

• Jmeter can be used to test performance for both static resources like JavaScript, HTML and dynamic resources like Servlets, AJAX, etc.
• With the help of Jmeter, we can generate and handle a large number of concurrent users.
• Jmeter is free to use with no licensing costs.
• Performance testing of many web applications is supported by Jmeter.
• It can be easily used and you don’t need much knowledge of coding for it.
• Features like Thread group can be used to see the software performance.
• Jmeter provides a graphical analysis of generated reports.

LoadRunner and Jmeter both are performance testing tools but it totally depends on the applications in which you are using this tool.

Jmeter is better due to the following reasons-

• Jmeter is an open-source tool that makes it highly accessible to enterprises and software businesses of all sizes.
• API Testing, Database Testing and MQ Tests can easily be done without any difficulties using Jmeter.
• Jmeter can easily run on multiple operating systems
• It is easy to install and provided unlimited load generation capacity.

But in the case of testing complex applications, Jmeter fails and due to its high consumption of memory, it causes errors. Then LoadRunner comes into the picture.

LoadRunner is better due to the following reasons-

• With this tool, users can do performance testing of existing legacy applications.
• It determines the root cause of issues in any application.
• It allows testers to do mobile and cloud testing.
• LoadRunner provides smaller test cycles to speed up the delivery process.

Jmeter Threads: Jmeter threads are used to execute the test plan entirely and it is independent of other threads. They indicate a single user, interacting with the application by sending them requests. When multiple users send multiple requests then that is called the Thread group.

Apache Jmeter has the capability to handle multiple threads in the same box and it can generate up to 200 threads per Jmeter instance. If in case a user needs more than that then, in that case, I would suggest you use multiple Jmeter instances. For your information, a modern machine can easily generate 500-1000 threads.

Yes, coding is required but depending on which performance tool you are using.

In the case of Jmeter, it requires a very little amount of coding as its GUI minimizes the requirement of coding needed to prepare a test plan.

In the case of Loadrunner, it is a must to know about the scripting language. If you are not able to write then you can’t use LoadRunner.

A workbench is a temporary storage area for the test elements. It has no relation with the Test Plan as components of the workbench won’t automatically get saved with the test plan. HTTP(s) Test script recorder is the most important part of the workbench as it records the HTTPS request and later users can apply load on them to measure the response time.  

As Jmeter and Selenium can integrate together, so selenium scripts can be run in Jmeter to get some ideas on their performance.

Ways to run it-

• Using Junit libraries we can build Selenium scripts, save them as Jars and copy them in the Jmeter directory.
• We can also add the Junit sampler to the respective test plan and then import the Jar file.
• Another way to run them is, add the Webdriver sampler plugin to the ext folder and after that restart the Jmeter. Write the selenium code in that sampler and execute the scripts to see their performance.

There are many ways to reduce the resources requirements in Jmeter, some of them are-

• By using a non-GUI mode to run the scripts: jmeter -n -t test.jmx -l test.jtl
• Using fewer listeners can also reduce the resources requirements. 
• Instead of using XML output use CSV output.
• Disable all Jmeter graphs when they are not in use as they consume a lot of memory.
• Instead of using the same Sampler, again and again, use them in a loop.
• Also, disable the “View Result Tree” listener because of the high consumption of memory.
• Before every test run clean the File tab.

Distributed Load Testing is the process in which heavy load is generated with the help of multiple load generators. In load testing reason for using multiple systems is to avoid generating a large number of users (threads) by a single system. In Jmeter we can achieve load testing by using Master-Slave configuration where all slaves can be controlled by the Master and the master is also responsible for collecting the test results.

NOTE: In this testing, all machines should be on the same network, and versions of Java and Jmeter should also be the same.

Apache Jmeter supports mainly three plugins that are used to generate high-quality results-

• Thread Group Plugin: This is the external plugin of Jmeter through which a spike test type workload model can be designed. Using this plugin user can apply conditional load on the server.
• Samplers Plugin: Through sampler plugins, Jmeter sends requests to a web server and wait for any response without running those requests.
• Listeners Plugin: These plugins provide a pictorial representation of collected data and write test results in a flexible format in the file.