Loadrunner interview questions and answers

LoadRunner
Interview
Questions
And
Answers
By:P2CInfotech

LoadRunner Interview Questions And Answers

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.

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.

Did u use LoadRunner? What version?
Yes. Version 7.2.

Explain the Load testing process?
Step 1: Planning the test. Here, we develop a clearly defined test plan to ensure the test scenarios
we develop will accomplish load-testing objectives.
Step 2: 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.
Step 3: 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 goaloriented scenario where we define the goal that our test has to achieve. LoadRunner
automatically builds a scenario for us.
Step 4: Running the scenario.
We emulate load on the server by instructing multiple Vusers 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.
Step 5: 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.
Step 6: 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.

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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.

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.

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.

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.

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.

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.

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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: Monitor the communication between the application and the server; Generate the
required function calls; and Insert the generated function calls into a Vuser script.

Why do you create parameters?
Parameters are like script variables. They are used to vary input to the server and to emulate real
users. Different sets of data are sent to the server each time the script is run. Better simulate the
usage model for more accurate testing from the Controller; one script can emulate many different
users on the system.

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.

How do you find out where correlation is required? Give few
examples from your projects?
Two ways: 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.

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.

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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.

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.

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.

How do you write user defined functions in LR? Give me few
functions you wrote in your previous 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.

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 c) Extended 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.
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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, set number of iterations.

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.

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‟

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.

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.

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.

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
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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.

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.

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.

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.

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

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.

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.

What does vuser_init action contain?
Vuser_init action contains procedures to login to a server.
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What does vuser_end action contain?
Vuser_end section contains log off procedures.

What is think time? How do you change the threshold?
Think time is the time that a real user waits between actions. Example: 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.

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:
Parameter substitution. Data returned by the server. Advanced trace.

Explain the following functions: - lr_debug_message
The lr_debug_message function sends a debug message to the output log when the specified
message class is set. lr_output_message - The lr_output_message function sends notifications to
the Controller Output window and the Vuser log file. lr_error_message - The lr_error_message
function sends an error message to the LoadRunner Output window. lrd_stmt - The lrd_stmt
function associates a character string (usually a SQL statement) with a cursor. This function sets
a SQL statement to be processed. lrd_fetch - The lrd_fetch function fetches the next row from
the result set.

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.

www.p2cinfotech.com

+1-732-546-3607


Loadrunner interview questions and answers

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