Loadrunner Interview Questions

[santhu]

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 9.0.
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 goal-oriented
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.
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.
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 fromweb 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.
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* (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.
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 errorâ€Â
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 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 “DatabaseÃ
¢â‚¬Â 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
Explain all the web recording options?
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.
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.
Throughput - If the throughput scales upward as time progresses and
the number of Vusers increase, this indicates that the bandwidth is
sufficient. If the graph were to remain relatively flat as the number
of Vusers increased, it would
be reasonable to conclude that the bandwidth is constraining the
volume of
data delivered.
Types of Goals in Goal-Oriented Scenario - Load Runner provides you
with five different types of goals in a goal oriented scenario:
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 that you want your scenario
Analysis Scenario (Bottlenecks): In Running Vuser graph correlated
with the response time graph you can see that as the number of Vusers
increases, the average response time of the check itinerary
transaction very gradually increases. In other words, the average
response time steadily increases as the load
increases. At 56 Vusers, there is a sudden, sharp increase in the
average response
time. We say that the test broke the server. That is the mean time
before failure (MTBF). The response time clearly began to degrade when
there were more than 56 Vusers running simultaneously.
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.
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.
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.