RAM, Memory Usage, CPU Usage, Paging in terms of LoadRunner

You are going to encounter these terms again and again on your journey to become a LoadRunner expert. We will clarify their meaning first, and shall see how are they related to LoadRunner.

Hard Disk vs RAM:

  1. Hard Disk is used for long-term storage of work while RAM is used to store your current work.
  2. Hard Disk holds the original copy of the program permanently while When you want to use a program, a temporary copy is put into RAM and that’s the copy you use.
  3. When working on a file, the original file is left untouched in the Hard Drive until you do a “save;” the “save” copies the new version of the file that’s in RAM onto the Hard Disk (and usually replaces the original file) while The file you are modifying, plus all the changes you make, are kept in RAM until you do a “save”

Download PDF for Full Explanation

Virtual Memory and Paging:

Virtual Memory is an essential part of all Operating Systems. As we saw above, RAM stores info about all the programs currently running on your desktop. If you open a program when RAM is full, your OS will try to locate programs on RAM which are not in use currently. It will then transfer those programs to some areas of hard disk, that ways space will be created on RAM for your new programs to run. So effectively, though there was no space on RAM but your OS created a memory space with the help of your hard disk. This memory is called as Virtual Memory. The area of hard disk where RAM image is copied is known as page file and process as paging.

You might ask why can’t we eliminate the use of hard disk or RAM, given the above scenario…here is a beautiful explanation of this, from the source cited below.

The read/write speed of a hard drive is much slower than RAM, and the technology of a hard drive is not geared toward accessing small pieces of data at a time. If your system has to rely too heavily on virtual memory, you will notice a significant performance drop. The key is to have enough RAM to handle everything you tend to work on simultaneously — then, the only time you “feel” the slowness of virtual memory is is when there’s a slight pause when you’re changing tasks. When that’s the case, virtual memory is perfect.
When it is not the case, the operating system has to constantly swap information back and forth between RAM and the hard disk. This is called thrashing, and it can make your computer feel incredibly slow.

Full Explanation here

CPU Usage:

It represent the percentage of time that a process used the CPU since the last update. The steps to find out current CPU usage:

Go to “Windows Task Manager” [Ctrl-Shift-Esc] > Performance > Top left graph shows you CPU usage as shown below.

LoadRunner CPU Usage

In terms of LoadRunner you should ensure that CPU usage should always be below (80-85)% on your loadgenerator machines for efficient functioning.

Memory usage:

It is the current working set of processes in kilobytes. In the above figure, Commit Charge (K) represents Memory usage. In terms of LoadRunner, you should ensure that Commit charge should always be less than Physical Memory (RAM) on your loadgenerator machines so that minimal paging is required.


11 Responses to “RAM, Memory Usage, CPU Usage, Paging in terms of LoadRunner”

  1. Hi,

    Can you plz explain :
    1.How to Find out bottlenecks in Loadrunner controller & solutions with an example? to analyse Loadrunner report? what are the points have to be consider?

    waiting for ur reply…



    Posted by Raghu | August 18, 2008, 2:18 pm
  2. Hi

    I have a doubt . For eg retrieving a list of records manually takes about 2 seconds but while running a baseline test in the controller for 1 vu for a couple of iterations takes 10 seconds . what could be the reason?

    Posted by laxmi | September 5, 2009, 6:58 pm
  3. this site is very good for learning loadrunner.really iam much comportble with the explanation

    Posted by moses | June 10, 2011, 2:43 pm
  4. Thanks for the clear explanation. It is simple, but very clear. Thanks a lot. Hard to find such a helpful site nowadays. :) Please continue this,

    Posted by blessy | September 6, 2011, 11:45 am
  5. Dear Team,

    Thank you for posting such a beautiful explanation about the things in LoadRunner in the website.I am very much happy to see a brand new website from you guys.

    However I just want to bring to your notice that “Full Explanation here ” link under Hard disk Vs RAM is not working

    the contents are removed from the server pointing to the link

    Please fix it.


    Posted by Suresh | February 12, 2012, 8:27 pm
  6. Thanks everyone.
    @Suresh: Thanks. The link is fixed now. You can download a PDF with explanation.

    Posted by Ankur | February 13, 2012, 7:44 pm
  7. LR 11.52; recent upgrade; now whenever have EVEN as few as 15 virtual users across 2 or more scenario groups connecting to loadgenerator, constantly get “Error: CPU usage for this load generator has exceeded 80%”. We routinely run 100-, 300-, 500-user WEB-based performance tests on controller to 4 load generators, using 80 or more scenario groups– so naturally have multiple scripts running (as threads) on each of 4 generators. Constantly get the “Error: CPU usage for this load generator has exceeded 80%”, which makes me doubt load test results, if generators are maxing out or even just spiking at 100& CPU (which perfmon indicates they are). Problem greatly increases, if run scripts as “process” vs. “threads.” HELP! I know we cannot be the only folks with this issue, upon upgrading to 11.52. We NEVER had this w/ Loadrunner 11.0. PLEASE HELP!!! Controller & generators all running Windows server 2008 R2 SP1, all with recommended (or above) LR specs. We have support through SAP (rather than HP); SAP seems to have never heard of this problem…

    Posted by David Graybeal | August 7, 2013, 7:27 pm


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