15 LoadRunner Interview Questions and Answers

LoadRunner is a leading performance testing tool used to identify and resolve system bottlenecks. It simulates user activity to test the performance and behavior of applications under load, making it essential for ensuring that software can handle high traffic and usage. With its robust capabilities, LoadRunner supports a wide range of protocols and integrates seamlessly with other testing tools, making it a versatile choice for performance engineers.

This article provides a curated selection of LoadRunner interview questions designed to help you demonstrate your expertise and problem-solving skills. By familiarizing yourself with these questions, you can confidently showcase your knowledge of performance testing and LoadRunner’s functionalities during your interview.

LoadRunner Interview Questions and Answers

1. What is a Vuser and how does it differ from a real user?

A Vuser, or Virtual User, in LoadRunner simulates a real user’s actions on an application. Vusers generate load on the system to measure its performance under various conditions. Unlike real users, Vusers are controlled by scripts that define their actions, such as logging in and performing transactions.

The main differences between a Vuser and a real user are:

• Automation: Vusers are automated and script-controlled, while real users interact manually.
• Scalability: Vusers can simulate thousands of users, unlike real users.
• Consistency: Vusers perform actions consistently as per the script, whereas real users may vary.
• Resource Utilization: Vusers use fewer resources, as they don’t need physical devices or human intervention.

2. How do you parameterize a script?

Parameterization in LoadRunner involves replacing hard-coded values in a script with parameters, allowing the script to use different data values during each test run. This simulates real-world scenarios where users interact with the application using varied data inputs, helping to avoid server-side caching and ensuring realistic testing conditions.

To parameterize a script:

• Identify values to be parameterized, such as user credentials or search terms.
• Create a parameter by selecting the value and choosing the Parameterize option.
• Define parameter properties, like name, data type, and data source.
• Configure parameter settings, including iteration and update frequency.
• Replace hard-coded values with parameters.

3. Explain the concept of correlation and provide an example scenario where it is necessary.

Correlation in LoadRunner captures dynamic values from server responses for use in subsequent requests, essential for handling session IDs and tokens that change with each session.

For example, when a user logs into a web application, the server generates a unique session ID needed for subsequent requests. Without correlation, the script would fail due to using an invalid static session ID.

In LoadRunner, correlation can be manual or automatic. Manually, you identify the dynamic value, create a correlation function to capture it, and use it in subsequent requests.

Example:

// Capture the session ID from the server response
web_reg_save_param("SessionID", "LB=Set-Cookie: session_id=", "RB=;", LAST);

// Login request
web_submit_data("login",
    "Action=http://example.com/login",
    "Method=POST",
    ITEMDATA,
    "Name=username", "Value=user", ENDITEM,
    "Name=password", "Value=pass", ENDITEM,
    LAST);

// Use the captured session ID in a subsequent request
web_url("dashboard",
    "URL=http://example.com/dashboard?session_id={SessionID}",
    LAST);

4. How do you analyze results in LoadRunner Analysis?

LoadRunner Analysis interprets performance test results to identify bottlenecks and understand application behavior. Key steps include:

• Load Test Results: Import results into LoadRunner Analysis, including response times, throughput, and other metrics.
• Graphs and Reports: Use graphs like Response Time and Throughput to visualize performance data.
• Transaction Analysis: Identify slow transactions to pinpoint areas needing optimization.
• Bottleneck Identification: Correlate metrics to identify bottlenecks, such as increased response time with more users.
• Error Analysis: Analyze errors to understand application stability and reliability.
• Comparative Analysis: Compare results from different test runs to assess changes’ impact.

5. Write a function to capture a dynamic value from a server response using C language.

Capturing dynamic values from server responses in LoadRunner is done using correlation functions in C language, such as web_reg_save_param.

Example:

web_reg_save_param("SessionID",
    "LB=Set-Cookie: session_id=",
    "RB=;",
    "Ord=1",
    LAST);

web_url("Login",
    "URL=http://example.com/login",
    "TargetFrame=",
    "Resource=0",
    "RecContentType=text/html",
    "Referer=",
    "Snapshot=t1.inf",
    "Mode=HTML",
    LAST);

Here, web_reg_save_param captures the session ID from the server response, with LB and RB defining the text surrounding the dynamic value.

6. What is the purpose of rendezvous points?

Rendezvous points in LoadRunner instruct multiple virtual users to perform a task simultaneously, simulating high load on the server. This helps identify performance bottlenecks and understand system behavior under peak conditions.

When a rendezvous point is inserted, Vusers wait until a specified number have reached it, then proceed together. This aids in stress testing the server and uncovering issues not apparent under normal load.

7. How can you customize the runtime settings for a Vuser script?

Customizing runtime settings for a Vuser script in LoadRunner is important for simulating real-world user behavior. These settings control aspects like pacing, think time, log settings, and error handling.

Key runtime settings include:

• Pacing: Controls the interval between script iterations, simulating realistic load.
• Think Time: Simulates user wait time between actions, mimicking real behavior.
• Log Settings: Determines log detail level, useful for debugging or analysis.
• Error Handling: Specifies Vuser response to errors, such as continuing or stopping.
• Browser Emulation: Specifies browser type and version for compatibility testing.

8. What are the different types of graphs available in LoadRunner Analysis?

LoadRunner Analysis offers various graphs to analyze performance test results, aiding in bottleneck identification and system behavior understanding. Graph types include:

• Running Vusers Graph: Shows the number of virtual users running during the test.
• Transaction Response Time Graph: Displays response time for each transaction.
• Hits per Second Graph: Illustrates server hits per second.
• Throughput Graph: Shows data transferred between client and server.
• Errors per Second Graph: Displays errors occurring per second.
• Transaction per Second Graph: Shows transactions completed per second.
• Average Transaction Response Time Graph: Displays average transaction response time.
• CPU Utilization Graph: Shows server CPU usage.
• Memory Utilization Graph: Displays server memory usage.
• Network Delay Graph: Illustrates network delay during the test.

9. Describe how you would monitor server resources during a test.

Monitoring server resources during a LoadRunner test involves tracking metrics like CPU usage, memory usage, disk I/O, and network I/O. LoadRunner provides tools for this:

• Controller: Manages load tests and provides real-time server resource monitoring.
• LoadRunner Agent: Installed on the server, it collects performance data for analysis.
• Analysis: Generates detailed reports and graphs post-test.

To monitor effectively:

• Set up monitoring profiles in the Controller.
• Use the LoadRunner Agent for data collection.
• Analyze data in real-time with the Controller’s dashboard.
• Generate reports using the Analysis component post-test.

10. Write a function to log custom messages to the LoadRunner output window.

In LoadRunner, log custom messages to the output window using lr_output_message. This is useful for debugging and tracking script execution.

Example:

lr_output_message("This is a custom log message.");

Use lr_error_message for error messages:

lr_error_message("This is an error message.");

And lr_log_message for messages with specific log levels:

lr_log_message("This is a log message with a specific log level.");

11. Explain the concept of think time and its importance in scripts.

Think time in LoadRunner simulates the delay between user actions, mimicking natural pauses users take when interacting with an application. It helps create realistic load scenarios that better represent actual user behavior.

Without think time, scripts execute actions rapidly, creating unrealistic load and potentially skewing performance metrics. Think time distributes load evenly, providing a more accurate representation of system performance under normal conditions.

In LoadRunner, think time is added using the lr_think_time function, specifying the pause duration between actions.

12. What are some best practices for scripting in LoadRunner?

When scripting in LoadRunner, following best practices ensures reliable, maintainable, and scalable performance tests. Consider these practices:

• Modularity: Break scripts into smaller, reusable actions or functions for easier management.
• Parameterization: Replace hard-coded values with parameters to simulate real-world scenarios.
• Error Handling: Implement robust error handling for unexpected events.
• Correlation: Capture and reuse dynamic server values to maintain session integrity.
• Think Time: Include think time to simulate real user behavior.
• Logging: Use logging judiciously to capture important information.
• Validation: Validate responses to ensure expected server results.

13. How do you identify performance bottlenecks using LoadRunner?

Identifying performance bottlenecks using LoadRunner involves:

• Script Creation and Execution: Create and execute test scripts simulating user actions.
• Load Testing: Use the Controller to set up and run load tests, defining scenarios and load distribution.
• Monitoring: Monitor system performance with LoadRunner’s built-in monitors, tracking metrics like CPU usage and response times.
• Analysis: Use LoadRunner’s Analysis tool to examine data and identify bottlenecks.
• Correlation and Diagnosis: Correlate performance data with application behavior to pinpoint bottlenecks.
• Reporting: Generate reports summarizing findings and recommendations.

14. Explain how you would perform load testing in a cloud environment using LoadRunner.

To perform load testing in a cloud environment using LoadRunner:

• Setup LoadRunner Environment: Install and configure LoadRunner, including Load Generators on cloud instances.
• Design Test Scenarios: Create scripts simulating user interactions with the application.
• Configure Cloud Load Generators: Provision cloud instances as Load Generators, integrating with cloud providers like AWS or Azure.
• Execute Load Test: Use the Controller to define test scenarios and monitor application performance in real-time.
• Analyze Results: Use LoadRunner Analysis to review metrics and identify performance bottlenecks.

15. How do you integrate LoadRunner with other performance monitoring tools?

LoadRunner integrates with performance monitoring tools for a comprehensive view of system performance during load testing. This allows correlation of LoadRunner’s metrics with system-level metrics, aiding in bottleneck identification.

Common tools for integration include:

• Dynatrace: Real-time application performance monitoring.
• AppDynamics: End-to-end application performance monitoring.
• New Relic: Insights into application performance and infrastructure.

Integration involves configuring LoadRunner to send test data to the monitoring tool and setting up the tool to receive and display this data, possibly requiring plugins or agents.