Loadrunner Interview Questions
- Thread starter anujsingh
- Start date
The following are some of the performance testing interviewquestions that will need some experience to answer. Try to keep these questions in mind while working on your performance test projects, so the interview preparation activity becomes a continuous process.
- What are the different scripting issues you faced so far?
- What are the performance bottlenecks that you found in projects you were working? What are the recommendations made to overcome those issues?
- Have you applied Little’s law in your project? If so, how?
- What is your approach for analysis?
- What do you monitor while execution?
- How to extract server data for test execution and how to analyze that?
- How to identify performance bottlenecks?
- Challenges that you face during scripting
- Correlation function
- Error handling
- Different recording modes for Web HTTP/HTML protocol.
- Scenario creation
- Challenges during execution
- Analysis
Some questions from my experience - hopefully will help someone
Scripting Skills
1. What is Think Time, Pacing – Easy Difficulty
How do you decide upon think time/pacing values.
Possible Answers –
Ø Using Littles Law formula - Number of users = Response Time * Transaction Per Second (TPS)
Ø Logical Derivation
2. Think Time Complex Difficulty
Can you calculate think time pacing values for following requirement – Single page script, customer wants 3600 transactions in 1 hour using 10 virtual users – Consider negligible response time.
Answer - 10 user need to do 3600 transaction => 1 User will do 360 transactions in 1 hour => 1 Iteration will need to be done in 3600/360 = 10 seconds
Pacing + Think Time = 10 Seconds
Think time should then be derived logically assuming the form length – eg - A single filed entry may take 2-3 seconds and remaining would be pacing.
3. Scenario Based : Average Difficulty
Question : Consider a scenario wherein while creating a test script in web/http protocol you need to handle a dynamically populated drop down box (Combo Box) and randomly pick up a value to be used in subsequent request
Possible Answer – This can be done using ’Correlation’ – Using “web_reg_save_param” load runner function and ORD= All attributes
Monitoring Questions:
1. Windows Monitoring –
Have you used perfmon?
What are the top 4 counters to be monitored using perfmon?
What is difference between user cpu/system cpu
2. Unix Monitoring –
How do you monitor unix flavored servers?
Have u used nmon, SAR, TOP, VMSTAT etc
3. Monitoring Tools :
Have you used HPD, Ganglia, Zabbix , Nagios etc
What counters do you monitor
4. APM Tools:
Exposure into dynatrace, Appdynamics, Wily etc
Performance Testing Questions (Definition based)
Easy Difficulty
What is 90th percent response time? - Answer - The response time value for a transaction below which 90% of the data points (response time values) lie, is called the 90 percentile response time.
Why 90th percentile response time is used and not average values? Answer - The Average Transaction Response Time graph displays the average time taken to perform transactions during each second of the load test scenario run. And the 90th percentile is the value for which 90% of the data points are smaller. 90th percentile gives you a more accurate picture removing the 10% outliers.
What is think Time and Pacing and Key differences?
What is IP spoofing – why is it used?
What graphs do you see during analysis?
Complex Difficulty
You are getting slow response when you click on a submit button – How will you identify the issue?
What is java thread dump – how do you analyze it?
How do you diagnose and solve memory leaks?
What are the various type of JVM logs?
What is DB profiling?
What are key sections of AWR report.
Scripting Skills
1. What is Think Time, Pacing – Easy Difficulty
How do you decide upon think time/pacing values.
Possible Answers –
Ø Using Littles Law formula - Number of users = Response Time * Transaction Per Second (TPS)
Ø Logical Derivation
2. Think Time Complex Difficulty
Can you calculate think time pacing values for following requirement – Single page script, customer wants 3600 transactions in 1 hour using 10 virtual users – Consider negligible response time.
Answer - 10 user need to do 3600 transaction => 1 User will do 360 transactions in 1 hour => 1 Iteration will need to be done in 3600/360 = 10 seconds
Pacing + Think Time = 10 Seconds
Think time should then be derived logically assuming the form length – eg - A single filed entry may take 2-3 seconds and remaining would be pacing.
3. Scenario Based : Average Difficulty
Question : Consider a scenario wherein while creating a test script in web/http protocol you need to handle a dynamically populated drop down box (Combo Box) and randomly pick up a value to be used in subsequent request
Possible Answer – This can be done using ’Correlation’ – Using “web_reg_save_param” load runner function and ORD= All attributes
Monitoring Questions:
1. Windows Monitoring –
Have you used perfmon?
What are the top 4 counters to be monitored using perfmon?
What is difference between user cpu/system cpu
2. Unix Monitoring –
How do you monitor unix flavored servers?
Have u used nmon, SAR, TOP, VMSTAT etc
3. Monitoring Tools :
Have you used HPD, Ganglia, Zabbix , Nagios etc
What counters do you monitor
4. APM Tools:
Exposure into dynatrace, Appdynamics, Wily etc
Performance Testing Questions (Definition based)
Easy Difficulty
What is 90th percent response time? - Answer - The response time value for a transaction below which 90% of the data points (response time values) lie, is called the 90 percentile response time.
Why 90th percentile response time is used and not average values? Answer - The Average Transaction Response Time graph displays the average time taken to perform transactions during each second of the load test scenario run. And the 90th percentile is the value for which 90% of the data points are smaller. 90th percentile gives you a more accurate picture removing the 10% outliers.
What is think Time and Pacing and Key differences?
What is IP spoofing – why is it used?
What graphs do you see during analysis?
Complex Difficulty
You are getting slow response when you click on a submit button – How will you identify the issue?
What is java thread dump – how do you analyze it?
How do you diagnose and solve memory leaks?
What are the various type of JVM logs?
What is DB profiling?
What are key sections of AWR report.
Some more questions – Primarily on loadrunner
1. What is the difference in running the Vuser as a process and as a thread? Which is more advantageous way of running Vuser?
Answer – Vuser as a process consumes a lot of memory and is heavier to rum –Vuser as thread is lighter and can help simulating a large number of virtual users. Hence You can run more number of Vusers on a single generator using the thread mode than the process mode.
2. What is parametrization in loadrunner?
Answer – Parameterization means to replace the hard coded value within the script and get data from CSV file. This allows a single Vuser to be run many times, and to use different data on each run. It helps in stimulating more real life server demand as it prevents server from caching results.
3. Why do you need text checks? What is the function which can be used for text check?
Answer – Text check ensures that page loads are proper during performance test executions. Text check can be done using loadrunner function web_reg_find
Example syntax - web_reg_find("Text=hello", "Search=Body", LAST);
Will look for text “hello” in html body and fail script if not found
4. How are response time and throughput (Transactions per second) related?
Answer – They are inversely proportional – If response time increases , TPS decreases.
5. How do you decide on protocol to use in loadrunner
Answer – By experience or protocol advisor.
6. What are the top 4 counters (Monitoring) you monitor at OS level.
Expected minimum answer – CPU, Memory, Disc and Network.
7. Syntax Questions
Q - Convert loadrunner parameter into integer number ?
Ans – Using loadrunner functions “atoi” and Lr_eval_string
Example - i = atoi(lr_eval_string("{prmCounter}"));
Q - How to save integer number to LoadRunner parameter?
Ans – Using Lr_save_int function
Example - int i;
i = 433;
lr_save_int(i, "prmCounter");
Scenario Based Questions (Best for understanding analytical skills):
1. There is a submit button on webpage which is responding very slowly (40 – 50 seconds response time) – What can be the issue? What will you do to identify the issue?
2. There is a sudden spike in response time at 12 midnight during the test ? What could have caused the spike ?
Most plausible answer – an housekeeping job eating up the cpu.
3. How do u diagnose a java memory leak ?
Approach – take memory dumps and compare object sizes over time.
4. Tell me about a scripting issue that you have faced and resolved in the past.
5. Tell me about one challenging performance issue and how you resolved it.
1. What is the difference in running the Vuser as a process and as a thread? Which is more advantageous way of running Vuser?
Answer – Vuser as a process consumes a lot of memory and is heavier to rum –Vuser as thread is lighter and can help simulating a large number of virtual users. Hence You can run more number of Vusers on a single generator using the thread mode than the process mode.
2. What is parametrization in loadrunner?
Answer – Parameterization means to replace the hard coded value within the script and get data from CSV file. This allows a single Vuser to be run many times, and to use different data on each run. It helps in stimulating more real life server demand as it prevents server from caching results.
3. Why do you need text checks? What is the function which can be used for text check?
Answer – Text check ensures that page loads are proper during performance test executions. Text check can be done using loadrunner function web_reg_find
Example syntax - web_reg_find("Text=hello", "Search=Body", LAST);
Will look for text “hello” in html body and fail script if not found
4. How are response time and throughput (Transactions per second) related?
Answer – They are inversely proportional – If response time increases , TPS decreases.
5. How do you decide on protocol to use in loadrunner
Answer – By experience or protocol advisor.
6. What are the top 4 counters (Monitoring) you monitor at OS level.
Expected minimum answer – CPU, Memory, Disc and Network.
7. Syntax Questions
Q - Convert loadrunner parameter into integer number ?
Ans – Using loadrunner functions “atoi” and Lr_eval_string
Example - i = atoi(lr_eval_string("{prmCounter}"));
Q - How to save integer number to LoadRunner parameter?
Ans – Using Lr_save_int function
Example - int i;
i = 433;
lr_save_int(i, "prmCounter");
Scenario Based Questions (Best for understanding analytical skills):
1. There is a submit button on webpage which is responding very slowly (40 – 50 seconds response time) – What can be the issue? What will you do to identify the issue?
2. There is a sudden spike in response time at 12 midnight during the test ? What could have caused the spike ?
Most plausible answer – an housekeeping job eating up the cpu.
3. How do u diagnose a java memory leak ?
Approach – take memory dumps and compare object sizes over time.
4. Tell me about a scripting issue that you have faced and resolved in the past.
5. Tell me about one challenging performance issue and how you resolved it.