Top most important Loadrunner interview questions and answers by Experts:
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1. What is the difference between Performance testing and Performance engineering?
In Performance testing, testing cycle includes requirement gathering, scripting, execution, result sharing and report generation. Performance Engineering is a step ahead of Performance testing where after execution; results are analyzed with the aim to find the performance bottlenecks and the solution is provided to resolve the identified issues.
2. Explain Performance Testing Life Cycle.
Step 1: System Analysis (Identification of critical transaction)
Virtual User Generator
Step 2: Creating Virtual User Scripts (Recording)
Step 3: Defining Users Behavior (Runtime setting)
Step 4: Creating Load Test Scenarios
Step 5: Running the Load Test Scenarios and Monitoring the Performance
Step 6: Analyzing the Results
Refer Performance Testing Tutorial #2 for more details.
3. What is Performance testing?
Performance testing is done to evaluate application`s performance under load and stress conditions. It is generally measured in terms of response time of user’s action on application.
4. What is Load testing?
Load testing is to determine if an application can work well with the heavy usage resulting from a large number of users using it simultaneously. Load is increased to to simulates the peak load that the servers are going to take during maximum usage periods.
5. What are the different components of LoadRunner?
The major components of LoadRunner are:
VUGen- Records Vuser scripts that emulate the actions of real users.
Controller – Administrative center for creating, maintaining and executing load test scenarios. Assigns scenarios to Vusers and load generators, starts and stops loading tests.
Load Generator – An agent through which we can generate load
Analysis – Provides graphs and reports that summarize the system performance
6. What is the Rendezvous point?
Rendezvous point helps in emulating heavy user load (request) on the server. This instructs Vusers to act simultaneously. When the vuser reaches the Rendezvous point, it waits for all Vusers with Rendezvous point. Once designated numbers of Vusers reaches it, the Vusers are released. Function lr_rendezvous is used to create the Rendezvous point. This can be inserted by:
1. Rendezvous button on the floating Recording toolbar while recording.
2. After recording Rendezvous point is inserted through Insert> Rendezvous.
7. What are the different sections of the script? In what sequence does these section runs?
LoadRunner script has three sections vuser_init, Action and vuser_end.
vuser_init has requests/actions to login to the application/server.
Action has actual code to test the functionality of the application. This can be played many times in iterations.
Vuser_end has requests/actions to login out the application/server.
The sequence in which these sections get executed is vuser_init is at the very beginning and vuser_end at the very end. Action is executed in between the two.
8. How do you identify which protocol to use for any application?
Previously Performance tester had to depend much on the development team to know about the protocol that application is using to interact with the server. Sometimes, it also used to be speculative.
However, LoadRunner provides a great help in form of Protocol Advisor from version 9.5 onwards. Protocol advisor detects the protocols that application uses and suggest us the possible protocols in which script can be created to simulate the real user.
9. What is correlation? Explain the difference between automatic correlation and manual correlation?
Correlation is used to handle the dynamic values in a script. The dynamic value could change for each user action (value changes when action is replayed by the same user) or for different users (value changes when action is replayed with different user). In both the cases correlation takes care of these values and prevents them from failing during execution.
Manual Correlation involves identifying the dynamic value, finding the first occurrence of dynamic value, identifying the unique boundaries of capturing the dynamic value, writing correlation function web_reg_save_param before the request having the first occurrence of dynamic value in its response.
Automated correlation works on predefined correlation rules. The script is played back and scanned for auto correlation on failing. Vugen identifies the place wherever the correlation rules work and correlate the value on approval.
Refer this tutorial for more details.
10. How to identify what to correlate and what to parameterize?
Any value in the script that changes on each iteration or with different user while replaying needs correlation. Any user input while recording should be parametrized.
11. What is parameterization & why is parameterization necessary in the script?
Replacing hard coded values within the script with a parameter is called Parameterization. This helps a single virtual user (vuser) to use different data on each run. This simulates real life usage of application as it avoids server from caching results.
Refer this tutorial for more details.
12. How you identify Performance test use cases of any application?
Test cases/Uses cases for Performance test are almost same as any manual/functional testing test cases where each and every step performed by the user is written. The only difference is that all manual test cases can’t be Performance testing use cases as there are few criteria for the selection as:
I. The user activity should be related to critical and most important functionality of the application.
II. The user activity should be having good amount of database activity such as search, delete or insert.
III. The user activity should be having good user volume. The functionality having less user activity is generally omitted from Performance testing point of view. e.g admin account activity.
Any of the manual test cases that fulfill the above criteria can be used as performance testing use case/test case. If manual test cases are not written step by step , Performance team should create dedicated documents for them.
13. While scripting you created correlation rules for automatic correlation. If you want to share the correlation rules with your team member working on the same application so that he/she can use the same on his workstation, how will you do that?
Correlation rules can be exported through .cor file and the same file can be imported through VuGen.
14. What are different types of vuser logs which can be used while scripting and execution? What is the difference between these logs? When you disable logging?
There are two types of Vuser logs available –Standard log and Extended log. Logs are key for debugging the script. Once a script is up and running, logging is enabled for errors only. Standard log creates a log of functions and messages sent to the server during script execution whereas Extended log contains additional of warnings and other messages. Logging is used during debugging and disabled while execution. Logging can be enabled for errors in that case.
15. What is Modular approach of scripting?
In Modular approach, a function is created for each request (e.g. login, logout, save, delete, etc.) and these functions are called wherever required. This approach gives more freedom to reuse the request and saves time. With this approach it is recommended to work with web custom request.
16. What are the different types goals in Goal-Oriented Scenario?
LoadRunner has five different types of goals in Goal-Oriented Scenario. These are:
• The number of concurrent Vusers
• The number of hits per second
• The number of transactions per second
• The number of pages per minute
• The transaction response time
17. How is each step validated in the script?
Each step in the script is validated with the content on the returned page. A content check verifies whether specific content is present on the web page or not. There are two types of content check which can be used in LoadRunner:
Text Check- This checks for a text/string on the web page
Image Check- This checks for an image on a web page.
18. How is VuGen script modified after recording?
Once the script is recorded, it can be modified with the following process:
19. What is Ramp up and Ramp Down?
Ramp up- Rate at which virtual users add to the load test
Ramp Down- Rate at which virtual users exit from the load test.
20. What is the advantage of running the Vuser as thread?
Running vusers as thread helps generate more virtual users from any machine due to small memory print of the vuser running as thread.
21. What is wasted time in VuGen Replay log?
Waste time is never performed by any browser user and just the time spent on the activities which support the test analysis. These activities are related to logging, keeping record and custom analysis.
22. How do you enable text and image checks in VuGen?
This can be done by using functions web_find (for text check) and web_image_check (for image check) and enabling image and text check from run time setting.
Run Time Setting–>Preference–>Enable the Image and text check box.
23. What is the difference between web_reg_find and web_find?
web_reg_find function is processed before the request sent and is placed before the request in the VuGen script whereas web_find function is processed after the response of the request come and is placed after the request in VuGen script.
24. What are the challenges that you will face to script the step “Select All” and then “Delete” for any mail account?
In this case the post for “Select All” and “Delete” will change every time depending on the number mails available. For this the recorded request for the two should be replaced with custom request and string building is required to build the post. (Note- This question needs practical knowledge. So please this practically and formulate your answer).
25. What is difference between pacing and think time?
Pacing is wait time between the action iterations whereas think time is wait time between the transactions.
26. What are the number of graphs you can monitor using Controller at a time? What is the max of them?
One, two, four and eight graphs can be seen at a time. The maximum number of graphs can be monitored in at a time is 8.
27. You have an application which shows the exam results of the student. Corresponding to name of each student its mentioned whether he passed or failed the exam with the label of “Pass” and “Fail”. How will you identify the number of passed and failed student in VuGen script?
For this text check is used for the web page for the text “Pass and “Fail”. Through the function web_reg_find, we can capture the number of texts found on the web page with the help of “SaveCount”. SaveCount stored the number of matches found. For example-
28. During the load test what is the optimum setting for Logs?
For the load test log level is set to minimal. This can be achieved with setting the log level to the standard log and selecting the radio button “Send message only when an error occurs”.
29. How will you handle the situation in scripting where for your mailbox you have to select any one mail randomly to read?
For this we will record the script for reading the first mail. Try to find what is being posted in the request to read the first mail such as mail ids or row no. From the post where a list of mails is reflecting, we will try to capture all the email ids row no with correlation function and keeping Ordinal as All i.e. ORD=All . Replace the requested email id in the read post with any of the randomly selected email id from the list of captured email ids.
Refer this Scripting Tutorial.
30. What is the Think Time? What is the Threshold level for think time and how can be this changed?
Think time is the wait time inserted intentionally between the actions in the script to emulate real user`s wait time while performing activity on the application. The Threshold level for Think time in the level below which recorded think time will be ignored. This can be changed from Recorded options->Script->Generate think time greater than threshold.
31. How is Automated Correlation configured?
Any setting related to Automated Correlation can be done byGeneral Options->Correlation. Correlation rules are set fromRecording options->Correlations.
32. How you decide the number of load generator machine required to run a test?
Number of load generator required totally depends on the protocol used to create the script and configuration of the load generator machine. Each protocol has different memory print and this decides how many virtual users can be generated from the give configuration of the machine (load generator).
33. What are the capabilities exactly you look for while selecting the performance testing tool?
Performance testing tool should capable of:-
• Testing an application built using multiple technologies and hardware platforms.
• Determine the suitability of a server for testing the application
• Testing an application with load of tens, thousand and even thousands virtual users.
34. How concurrent users are differing from simultaneous users?
All simultaneous users are concurrent users but vice versa is not true.
All the vusers in the running scenario are Concurrent users as they are using the same application at the same time but may be or may not be doing the same tasks. Simultaneous users perform the same task at the same time. Concurrent users are made Simultaneous users through rendezvous points. Rendezvous points instruct the system to wait till a certain number of vusers arrive so that they all can do a particular task simultaneously.
35. How do you identify which values need to be correlated in the script? Give an example.
This can be done in ways:
a) Record the two scripts with similar steps and compare them using WDiff utility. (See tutorial Correlation).
b) Replay the recorded script and scan for correlation. This gives a list of values that can be correlated.
Session Id is a good example of this. When two scripts are recorded and compared using WDiff utility. Session ids in the two scripts should be different and WDiff highlight these values.
36. How does caching affect performance testing results?
When data is cached in server`s memory, the server need not fetch the result and no server activity triggered. Test result does not reflect the same performance of real user using the application with different data.
37. How will you stop the execution of script on error?
This can be achieved through lr_abort function. The function instructs the vuser to stop executing Action section and end the execution by executing the vuser_end section. This function is helpful in handling a specific error. This can also be used to handle a situation rather than error where execution is not possible. The function assigned “Stopped” status to the vuser which stopped due to lr_abort function. In Run-Time setting, “Continue on error” should be unchecked.
38. What is load testing?
Load testing is to test that if the application works well with the loads from large number of simultaneous users and transactions. It also used to determine whether it can handle peak usage periods.
39. What is load runner?
Load Runner is a performance testing tool from HP. This tool supports all aspects such as Load, Stress, Endurance, data volume and spike Testing.
40. What are all the components of LoadRunner?
Following are the components of LoadRunner
• The Virtual User Generator
• Controller, and the Agent process
• LoadRunner Analysis and Monitoring
• LoadRunner Books Online
41. What Component of LoadRunner is used to record a script?
The Virtual User Generator (VuGen) component is used to record a script and it enables you to develop Vuser scripts for a variety of application types and communication protocols.
42. What is a rendezvous point?
Rendezvous points are introduced into Vuser scripts to simulate more users on the server. Rendezvous points instruct Vusers to wait during test execution in order to perform the tasks simultaneously.
For example, in a banking application, Rendezvous points are inserted for 100+ multiple users to deposit money simultaneously.
43. What is a scenario?
A scenario is nothing but an event that occurs for each testing session.
For example, a scenario defines
• Number of users
• Action to be performed
• Virtual machines system
44. How can we debug a LoadRunner script?
VuGen contains two options to debug Vuser scripts
• Run Step by Step command and
We can also manually set the message class within your script using the lr_set_debug_message function.
45. How can we perform functional testing under load?
Functionality under load can be tested by running several Vusers concurrently. By increasing the Vusers, it is necessary to determine how much load the server can sustain.
46. What is the relationship between Response Time and Throughput?
The Throughput shows the amount of data in bytes that the Vusers received from the server in a second. When It is compared with transaction response time, throughput and response time get decreased.
The peak throughput and highest response time would occur approximately at the same time.
47. What does vuser_init and vuser_end action contain?
Vuser_init action contains procedures to login to a server and Vuser_end section contains log off procedures.
48. What is the difference between standard log and extended log?
The standard log sends a subset of functions and messages to the output log and subset of functions depends on the Vuser type.
Extended log sends a detailed script execution messages to the output log. It is mainly used during debugging when user needs information about Parameter substitution.
49. What are all the types of Goals in Goal-Oriented Scenario of Load Runner?
Load Runner provides you with five different types of goals:
• Number of concurrent Vusers
• Number of hits per second
• Number of transactions per second
• Number of pages per minute
• Transaction response time
50. What is a function to capture dynamic values in the web vuser script?
Web_reg_save_param is the function that saves dynamic data information to a parameter.
51. What are the Load Runner testing process?
Following are the testing process in LoadRunner:
• Plan load test
• Create Vuser Scripts
• Define Scenario
• Run Scenario
• Analyze results
52. What is remote command launcher?
The remote command launcher enables the controller to start applications in the host machine.
53. How can we develop the database vuser script?
Vuser scripts can be developed either by recording with the load vuser script generator or by using Load runner vuser script template.
54. How do you load a load runner Agent?
While running the scenario, loadrunner controller instructs the remote agent dispatcher to launch loadrunner agent. The controller instructs the loadrunner agent to initialize, run, pause and stop the vusers.
55. What is the difference between hits/second and requests/second?
Hits per second means the number of hits the server receives in one second from the vuser.
Request per second is the number of request the vuser will request from the server.
56. What are the advantages of load runner?
Following are the advantages of Load Runner:
• Reduces human intervention
• Reduces the requirement of the systems
• Helps in the better usage of time and money
• Effective utilization of automation
• Single point execution
57. What is the vuser in the scenario?
The vuser is the virtual users who can simulate the real users. The virtual users who take the place of real users’s operating client software, such as IE sending requests using the HTTP protocol to IIS or Apache web servers.
58. How do we write a user defined function in LoadRunner?
Use should create the external library that contains the function. This library must then be added to the bin directory of VuGen. And then, the user-defined function can be assigned as a parameter.
59. What are the changes that can be made to run-time settings?
There are four run-time settings that can be made:
• Pacing: This contains iteration count.
• Log: Logging can be set to standard or disabled.
• Think Time: Capable of setting think time to be ignored or replayed.
• General: Allows the setting of Vusers for processes or multithreading.
60. How can we find database related issues?
Monitors and the Data Resource Graph can be used to find database related issues. LoadRunner allow the tester to specify the resource that needs to be measured before the controller is run.
61. How many types of graphs are available in LoadRunner?
There are 5 types of graphs:
• Network delay time graph – displays the time that elapses between request and response
• Two transaction response time graphs – one transation response time graph for load and another one for percentile
• Hits/second graph – Shows application traffic volume
• Pages download/second graph – shows the rate at which pages are downloaded per second
62. How can performance bottlenecks can be identified?
Monitors can be used to detect performance bottlenecks. These include network, web server, application server, and database server monitors.
These monitors can be used to locate trouble spots in scenarios that cause increase in response time and throughput, network delays, performance response time, hits/second, etc.
63. What is ramp up and how it can be set?
Ramp up is gradually increasing the load on a server and can be simulated by gradually increasing the number of Vusers. This feature can be found in the Scenario Scheduling Options.
64. How correlation can be performed?
Correlation can be performed in two ways:
• Use the scan function to search for correlations and select a value from the result.
• Record a pair of scripts and then compare them to each other.
65. Where are automatic correlation options set?
The automatic correlation is set in recording options area on the correlation tab. Correlation can be enabled for the full script and rules for correlation can be defined.
Automatic correlation can be performed on a database by viewing the output window, scanning for correlation, and selecting the value that will be used.
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