Load Runner FAQs

1)Difference between concurrent and simultaneous vuser?

This is one of the most frequently asked questions from LoadRunner newbies. If we go by the literal meaning from Dictionary.Com both are same but from LoadRunner’s perspective there is a slight difference.

All the vusers in a particular scenario are called Concurrent vusers. They may or may not perform the same tasks. On the other hand simultaneous vusers is more to do withrendezvous points. When we set rendezvous points we instruct the system to wait till a certain no of vusers arrive so that they all can do a particular task simultaneously. These vusers performing the same task at the same time are called Simultaneous vusers.

For example in a Yahoo Mail application: Suppose a scenario consists of 100 vusers with 3 tasks – 1) Login, 2) Check no of unread mails 3) Logout. Vusers at 1) + 2) + 3) will be called as concurrent vusers as they are part of same scenario performing some task but if have set a rendezvous point so that say 25 vuser perform the 2) task at the same time these 25 vusers would be termed as simultaneous vusers.

2)What is memory leak, page fault and how they affect LoadRunner performance?

memory leak:

A memory leak is a particular type of unintentional memory consumption by a computer program where the program fails to release memory when no longer needed. This condition is normally the result of a bug in a program that prevents it from freeing up memory that it no longer needs.This term has the potential to be confusing, since memory is not physically lost from the computer. Rather, memory is allocated to a program, and that program subsequently loses the ability to access it due to program logic flaws.

page fault:

An interrupt that occurs when a program requests data that is not currently in real memory. The interrupt triggers the operating system to fetch the data from a virtual memory and load it into RAM.

An invalid page fault or page fault error occurs when the operating system cannot find the data in virtual memory. This usually happens when the virtual memory area, or the table that maps virtual addresses to real addresses, becomes corrupt.

Now the most important question comes up, how do they affect

LoadRunner functioning:

As you might guess, memory leak, if left unattended and not corrected, could prove to be fatal. Memory leaks can be found out by running tests for long duration (say about an hour) and continuously checking memory usage.

Issues caused by memory leaks are essentially based on two variable for a standalone windows application 1) Frequency of usage 2) size of memory leak . If either one or both are very high it could cause the computer to come to a point when no memory is available for other applications causing it to crash. If it is a network based application then you will also have to consider network traffic . If each network transaction causes a memory leak , then a high volume of network transactions could also prove dangerous.