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LoadRunner Interview Questions and Answers | LoadRunner FAQ's
LoadRunner Interview Questions and FAQ's
1. What is load testing?
Load testing is to test that if the application works fine with the loads that result from large number of simultaneous users, transactions and to determine weather it can handle peak usage periods.
2. What is Performance testing?
Timing for both read and update transactions should be gathered to determine whether system functions are being performed in an acceptable timeframe. This should be done standalone and then in a multi user environment to determine the effect of multiple transactions on the timing of a single transaction.
3.Did u use LoadRunner? What version?
Yes. Version 7.2.
4. Explain the Load testing process?
step1: Planning the test
Here, we develop a clearly defined test plan to ensure the test scenarios we develop will accomplish load-testing objectives.
step2: Creating Vusers
Here, we create Vuser scripts that contain tasks performed by each Vuser, tasks performed by Vusers as a whole, and tasks measured as transactions.
step3: Creating the scenario
A scenario describes the events that occur during a testing session. It includes a list of machines, scripts, and Vusers that run during the scenario. We create scenarios using LoadRunner Controller. We can create manual scenarios as well as goal-oriented scenarios. In manual scenarios, we define the number of Vusers, the load generator machines, and percentage of Vusers to be assigned to each script. For web tests, we may create a goal-oriented scenario where we define the goal that our test has to achieve. LoadRunner automatically builds a scenario for us.
step4: Running the scenario
We emulate load on the server by instructing multiple Vusres to perform tasks simultaneously. Before the testing, we set the scenario configuration and scheduling. We can run the entire scenario, Vuser groups, or individual Vusers.
step5: Monitoring the scenario
We monitor scenario execution using the LoadRunner online runtime, transaction, system resource, Web resource, Web server resource, Web application server resource, database server resource, network delay, streaming media resource, firewall server resource, ERP server resource, and Java performance monitors.
step6: Analyzing test results
During scenario execution, LoadRunner records the performance of the application under different loads. We use LoadRunner’s graphs and reports to analyze the application’s performance.
5. When do you do load and performance Testing?
We perform load testing once we are done with interface (GUI) testing. Modern system architectures are large and complex. Whereas single user testing primarily on functionality and user interface of a system component, application testing focuses on performance and reliability of an entire system. For example, a typical application-testing scenario might depict 1000 users logging in simultaneously to a system. This gives rise to issues such as what is the response time of the system, does it crash, will it go with different software applications and platforms, can it hold so many hundreds and thousands of users, etc. This is when we set do load and performance testing.
6. What are the components of LoadRunner?
The components of LoadRunner are The Virtual User Generator, Controller, and the Agent process, LoadRunner Analysis and Monitoring, LoadRunner Books Online.
7. What Component of LoadRunner would you use to record a Script?
The Virtual User Generator (VuGen) component is used to record a script. It enables you to develop Vuser scripts for a variety of application types and communication protocols.
8. What Component of LoadRunner would you use to play back the script in multi user mode?
The Controller component is used to playback the script in multi-user mode. This is done during a scenario run where a vuser script is executed by a number of vusers in a group.
9. What is a rendezvous point?
You insert rendezvous points into Vuser scripts to emulate heavy user load on the server. Rendezvous points instruct Vusers to wait during test execution for multiple Vusers to arrive at a certain point, in order that they may simultaneously perform a task. For example, to emulate peak load on the bank server, you can insert a rendezvous point instructing 100 Vusers to deposit cash into their accounts at the same time.
10. What is a scenario?
A scenario defines the events that occur during each testing session. For example, a scenario defines and controls the number of users to emulate, the actions to be performed, and the machines on which the virtual users run their emulations.
11. Explain the recording mode for web vuser script?
We use VuGen to develop a Vuser script by recording a user performing typical business processes on a client application. VuGen creates the script by recording the activity between the client and the server. For example, in web based applications, VuGen monitors the client end of the database and traces all the requests sent to, and received from, the database server.
We use VuGen to:
a) Monitor the communication between the application and the server;
b) Generate the required function calls; and
c) Insert the generated function calls into a Vuser script.
12. Why do you create parameters?
Parameters are like script variables. They are used to vary input to the server and to emulate real users.
a) Different sets of data are sent to the server each time the script is run.
b) Better simulate the usage model for more accurate testing from the Controller, one script can emulate many different users on the system.
13. What is correlation? Explain the difference between automatic correlation and manual correlation?
Correlation is used to obtain data which are unique for each run of the script and which are generated by nested queries. Correlation provides the value to avoid errors arising out of duplicate values and also optimizing the code(to avoid nested queries). Automatic correlation is where we set some rules for correlation. It can be application server specific. Here values are replaced by data which are created by these rules. In manual correlation, the value we want to correlate is scanned and create correlation is used to correlate.
14. How do you find out where correlation is required? Give few examples from your projects?
First we can scan for correlations, and see the list of values which can be correlated. From this we can pick a value to be correlated. Secondly, we can record two scripts and compare them. We can look up the difference file to see for the values which needed to be correlated.
In my project, there was a unique id developed for each customer, it was nothing but Insurance Number, it was generated automatically and it was sequential and this value was unique. I had to correlate this value, in order to avoid errors while running my script. I did using scan for correlation.
15. Where do you set automatic correlation options?
Automatic correlation from web point of view, can be set in recording options and correlation tab. Here we can enable correlation for the entire script and choose either issue online messages or offline actions, where we can define rules for that correlation.
Automatic correlation for database, can be done using show output window and scan for correlation and picking the correlate query tab and choose which query value we want to correlate. If we know the specific value to be correlated, we just do create correlation for the value and specify how the value to be created.
16. What is a function to capture dynamic values in the web vuser script?
Web_reg_save_param function saves dynamic data information to a parameter.
17. When do you disable log in Virtual User Generator, When do you choose standard and extended logs?
Once we debug our script and verify that it is functional, we can enable logging for errors only. When we add a script to a scenario, logging is automatically disabled.
Standard Log Option:
When you select Standard log, it creates a standard log of functions and messages sent during script execution to use for debugging. Disable this option for large load testing scenarios. When you copy a script to a scenario, logging is automatically disabled
Extended Log Option:
Select extended log to create an extended log, including warnings and other messages. Disable this option for large load testing scenarios. When you copy a script to a scenario, logging is automatically disabled. We can specify which additional information should be added to the extended log using the extended log options.
18. How do you debug a LoadRunner script?
VuGen contains two options to help debug Vuser scripts-the Run Step by Step command and breakpoints. The Debug settings in the Options dialog box allow us to determine the extent of the trace to be performed during scenario execution. The debug information is written to the Output window.
We can manually set the message class within your script using the lr_set_debug_message function. This is useful if we want to receive debug information about a small section of the script only.
19. How do you write user defined functions in LR? Give me few functions you wrote in your pvious project?
Before we create the User Defined functions we need to create the external library(DLL) with the function. We add this library to VuGen bin directory. Once the library is added then we assign user defined function as a parameter. The function should have the following format:
__declspec (dllexport) char* <function name>(char*,char*)
Examples of user defined functions are as follows:
GetVersion, GetCurrentTime, GetPltform are some of the user defined functions used in my earlier project.
20. What are the changes you can make in run-time settings?
The Run Time Settings that we make are:
A) Pacing - It has iteration count.
b) Log - Under this we have Disable Logging Standard Log and Extended.
c) Think Time - In think time we have two options like Ignore think time and Replay think time.
D) General - Under general tab we can set the vusers as process or as multithreading and whether each step as a transaction.
21. Where do you set Iteration for Vuser testing?
We set Iterations in the Run Time Settings of the VuGen. The navigation for this is Run time settings, Pacing tab, and set number of iterations.
22. How do you perform functional testing under load?
Functionality under load can be tested by running several Vusers concurrently. By increasing the amount of Vusers, we can determine how much load the server can sustain.
23. What is Ramp up? How do you set this?
This option is used to gradually increase the amount of Vusers/load on the server. An initial value is set and a value to wait between intervals can be specified.
To set Ramp Up, go to 'Scenario Scheduling Options'
24. What is the advantage of running the vuser as thread?
VuGen provides the facility to use multithreading. This enables more Vusers to be run per generator.
If the Vuser is run as a process, the same driver program is loaded into memory for each Vuser, thus taking up a large amount of memory. This limits the number of Vusers that can be run on a single generator.
If the Vuser is run as a thread, only one instance of the driver program is loaded into memory for the given number of Vusers(say 100). Each thread shares the memory of the parent driver program, thus enabling more Vusers to be run per generator.
25. If you want to stop the execution of your script on error, how do you do that?
The lr_abort function aborts the execution of a Vuser script. It instructs the Vuser to stop executing the Actions section, execute the vuser_end section and end the execution. This function is useful when you need to manually abort a script execution as a result of a specific error condition. When you end a script using this function, the Vuser is assigned the status "Stopped". For this to take effect, we have to first uncheck the “Continue on error” option in Run-Time Settings.
26. What is the relation between Response Time and Throughput?
The Throughput graph shows the amount of data in bytes that the Vusers received from the server in a second. When we compare this with the transaction response time, we will notice that as throughput decreased, the response time also decreased. Similarly, the peak throughput and highest response time would occur approximately at the same time.
27. Explain the Configuration of your systems?
The configuration of our systems refers to that of the client machines on which we run the Vusers. The configuration of any client machine includes its hardware settings, memory, operating system, software applications, development tools, etc. This system component configuration should match with the overall system configuration that would include the network infrastructure, the web server, the database server, and any other components that go with this larger system so as to achieve the load testing objectives.
28. How do you identify the performance bottlenecks?
Performance Bottlenecks can be detected by using monitors. These monitors might be application server monitors, web server monitors , database server monitors and network monitors. They help in finding out the troubled area in our scenario which causes increased response time. The measurements made are usually performance response time, throughput, hits/sec, network delay graphs, etc.
29. If web server, database and Network are all fine where could be the problem?
The problem could be in the system itself or in the application server or in the code written for the application.
30. How did you find web server related issues?
Using Web resource monitors we can find the performance of web servers. Using these monitors we can analyze throughput on the web server, number of hits per second that occurred during scenario, the number of http responses per second, the number of downloaded pages per second.
31. How did you find database related issues?
By running “Database” monitor and help of “Data Resource Graph” we can find database related issues. E.g. you can specify the resource you want to measure on before running the controller and than you can see database related issues
32. Explain all the web recording options?
33. What is the difference between Overlay graph and Correlate graph?
Overlay Graph : It overlay the content of two graphs that shares a common x-axis. Left Y-axis on the merged graph show’s the current graph’s value & Right Y-axis show the value of Y-axis of the graph that was merged.
Correlate Graph: Plot the Y-axis of two graphs against each other. The active graph’s Y-axis becomes X-axis of merged graph. Y-axis of the graph that was merged becomes merged graph’s Y-axis.
34. How did you plan the Load? What are the Criteria?
Load test is planned to decide the number of users, what kind of machines we are going to use and from where they are run. It is based on 2 important documents, Task Distribution Diagram and Transaction profile. Task Distribution Diagram gives us the information on number of users for a particular transaction and the time of the load. The peak usage and off-usage are decided from this Diagram. Transaction profile gives us the information about the transactions name and their priority levels with regard to the scenario we are deciding.
35. What does vuser_init action contain?
Vuser_init action contains procedures to login to a server.
36. What does vuser_end action contain?
Vuser_end section contains log off procedures.
37. What is think time? How do you change the threshold?
Think time is the time that a real user waits between actions.
When a user receives data from a server, the user may wait several seconds to review the data before responding. This delay is known as the think time.
Changing the Threshold:
Threshold level is the level below which the recorded think time will be ignored. The default value is five (5) seconds. We can change the think time threshold in the Recording options of the Vugen.
38. What is the difference between standard log and extended log?
The standard log sends a subset of functions and messages sent during script execution to a log. The subset depends on the Vuser type
Extended log sends a detailed script execution messages to the output log. This is mainly used during debugging when we want information about:
a) Parameter substitution
b) Data returned by the server
c) Advanced trace
39. Explain the following functions:
The lr_debug_message function sends a debug message to the output log when the specified message class is set.
The lr_output_message function sends notifications to the Controller Output window and the Vuser log file.
The lr_error_message function sends an error message to the LoadRunner Output window.
The lrd_stmt function associates a character string (usually a SQL statement) with a cursor. This function sets a SQL statement to be processed.
The lrd_fetch function fetches the next row from the result set.
1. What are the three sections of a Vuser script and what is the purpose of each one?
1) Vuser_init - used for recording the logon.
2) Actions - used for recording the business process.
3) Vuser_end - used for recording the logoff.
2. For what purpose are Vusers created?
Vusers are created to emulate real users acting on the server for the purpose of
3. What are the benefits of multiple Action files within a Vuser?
They allow you to perform different business processes in one Vuser to repsent
A real user who does the same thing. They let you build Vusers that emulate real
Users defined in the User Community Profile. They also allow you to record the
Login and logoff separately from the Action files and thus to avoid iteration.
4. How can you tell the difference between an integer value and a string value
In a VuGen script?
Strings are enclosed in quotes; integers are not.
5. What is the purpose of a LoadRunner transaction?
To measure one or more steps/user actions of a business process.
6. What is the easiest way to get measurements for each step of a recorded script?
For the entire action file?
Enable automatic transactions.(Runtime settings, Recording Options)
7. When would you parameterize a value rather than correlate queries?
Parameterize a value only when it is input by the user.
8. What are the four selection methods when choosing data from a data file?
Sequential, Random, Unique, and Same line as <parameter_name>.
9. How can reusing the same data during iterative execution of a business process
Negatively affect load testing results?
In reusing the same data for each iteration, the server recognizes the same data is
Requested and places it in its cache. The load test then gets performance results
That is not based on real server activity but caching. This will not provide the correct
Results during the analysis of the load test.
10. How can caching negatively affect load testing results?
When data is cached in the server’s memory, the server does not need to fetch it
From the database during playback. Then, test results do not reflect the same performance they would if real users were loading the system with different data.
11. Why is it recommended to add verification checks to your Vusers?
You would want to verify, using LoadRunner that the business process is functioning
As expected under load.
12. When does VuGen record a web_submit_data instead of a web_submit_form?
Why? (Be as specific as possible)
A web_submit_data is recorded when VuGen cannot match the action, method,
Data fields, and/or hidden data values with the page that is stored in the record
Proxy cache. Comparison failures are typically caused by something other than
HTML setting the properties of the HTTP request. Because VuGen can parse only
HTML, it cannot find all the properties of the HTTP request in memory. This
Results in the hard-coding of all the request information in a web_submit_data
13. What do you need to do to be able to view parameter substitution in the Execution
Check extended log and Parameter substitution in the Run-Time Settings.
14. How can you determine which field is data dependent?
Rerecord the same script using different input values, then compare the two
15. Where should the rendezvous is placed in the script?
The rendezvous should be placed immediately before the transaction where you
want to create peak load. In this case, the rendezvous should be placed right
before starting the Update Order transaction.
16. For what purpose should you select continue on error?
Set it only when making Execution Logs more descriptive or adding logic to the
17. What is the purpose of selecting Show browser during replay in the General
This setting allows you to see the pages that appear during playback. This is useful
for debugging your Vuser during the initial stages of Web Vuser creation.
18. What tools does VuGen provide to help you analyze Vuser run results?
Execution Log, Run-Time Viewer, and Mercury Test Results window.
19. If your Vuser script had two parameters, “Depart City” and “Arrival City,” how
could you have the Vuser script return an error message which included the city
lr_error_message (“The Vuser could not submit the reservation request for %s to
%s”, (lr_eval_string (“”), lr_eval_string (“”));
20. Why should you run more Vusers than your anticipated peak load?
(1) To test the scalability of the system.
(2) To see what happens when there is a spike in system usage.
21. What is difference between manual scenario and Goal oriented scenario? What
Goal Oriented scenarios can be created?
–Main purpose is to learn how many Vusers can run concurrently
– Gives you manual control over how many Vusers run and at what times
Goal oriented scenario:
– Goal may be throughput, response time, or number of concurrent Vusers
– LoadRunner manages Vusers automatically
Different Goal Oriented Scenarios are:
- Virtual Users
- Hits per second
- Transaction per second
- Transaction Response time
- Pages per minute
22. Why wouldn’t you want to run virtual users on the same host as the Load-
Runner Controller or Database Server?
Running virtual users on the same host as the LoadRunner Controller will skew
the results so that they no longer emulate real life usage. By having both the Controller
and the Vusers on the same machine, the tester will not be able to determine
the effects of the network traffic.
23. Each time you run the same scenario, the results will be slightly different. What
are some of the factors that can cause differences in performance measurements?
Different factors can effect the performance measurements including network
traffic, CPU usage and caching.
24. What are some of the reasons to use the Server Resources Monitor?
To find out how much data is coming from the cache
T o help find out what parts of the system might contain bottlenecks
25. Explain the following:
- Hits per second graph
The Hits per Second graph shows the number of HTTP requests made by Vusers to the Web server during each second of the scenario run. This graph helps you evaluate the amount of load Vusers generate, in terms of the number of hits.
- Pages download per second graph
The Pages Downloaded per Second graph shows the number of Web pages (y-axis) downloaded from the server during each second of the scenario run (x-axis). This graph helps you evaluate the amount of load Vusers generate, in terms of the number of pages downloaded.
- Transaction Response time (under load) graph
The Transaction Response Time (Under Load) graph is a combination of the Running Vusers and Average Transaction Response Time graphs and indicates transaction times relative to the number of Vusers running at any given point during the scenario. This graph helps you view the general impact of Vuser load on performance time and is most useful when analyzing a scenario with a gradual load.
- Transaction Response time (percentile) graph
The Transaction Response Time (Percentile) graph analyzes the percentage of transactions that were performed within a given time range. This graph helps you determine the percentage of transactions that met the performance criteria defined for your system.
- Network delay time graph
The Network Delay Time graph shows the delays for the complete path between the source and destination machines (for example, the database server and Vuser load generator).
1. What are the different Vuser types?
2. What are the different phases in Loadrunner?
3. What are the components of LoadRunner?
4. What are the changes you can make in run-time settings?
5. What is a transaction in LoadRunner?
6. What is a scenario?
7. What is the difference between iteration and vusers?
8. What are the sections of Vuser Script?
9. What does vuser_init contain?
10. What does vuser_end contain?
11. What is a rendezvous point?
12. What are 2 modes in LoadRunner?
13. Which analysis tools did you use?
14. Where do you set Iteration for Vuser testing?
15. Did u use LoadRunner? What version?
16. Which tool did you use to recorded code in Load Runner?
17. What is the relation between Response Time and Throughput?
18. Explain Throughput and Hits per second?
19. Explain the Configuration of your systems?
20. How did you plan the Load? What are the Criteria?
21. When did you decide to do Load Testing?
22. What is cross-scenario analysis?
23. Why do you create parameters?
24. What is correlation?
25. Why do you compare two scripts? How you do that?
26. What are the different graphs in LoadRunner?
27. What are the different reports in LoadRunner?
28. When do you disable logging, When do you choose standard and extended logs?
29. What is the function of web_create_html_param?
30. How do you synchronize the scripts in LoadRunner?
31. Modes of logging in LoadRunner?
32. Types of extend logging?
33. How many times you can run a script?
34. How do we parameterize?
35. How do you plan load test?
36. How do you identify the bottlenecks in load test?
37. If web server, database and Network are all fine where could be the problem?
38. How would you know that it’s a resource contention problem?
39. How did you report web server related issues?
40. How did you report database related issues?
41. what are three main components in LoadRunner?
42. What are three modes of LoadRunner Logging?
43. Which mode would you use to debug a LoadRunner script?
44. What are three types of Extend log?
45. Where do you set how many times a LoadRunner script should repeat?
46. What steps would you use to replace data in a script with a Parameter?
47. What is the LoadRunner for web statement used to performer a Text check?
48. What are LoadRunner for web correlation function?
49. What is a rendezvous point
50. What is think time? How do you change the threshold?
51. what is the difference between standard log and extended log?