Difference between concurrent and simultaneous vuser

concurrent vs 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 with rendezvous 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.


10 Responses to “Difference between concurrent and simultaneous vuser”

  1. can you please revisit your statement. I guess the explanation given here is vice versa.Because normally the Simulataneous Users are always greater than concurrent users. when we take a banking application, simultaneous users would be 50000 users whereas concurrent users would be 5000 only.
    Please correct me if i am wrong.

    Posted by Jacintha | January 16, 2009, 5:33 pm
  2. That’s why I made it as a seperate post. There is a lot of confusion regarding these terms.

    You may want to check the ongoing discussion at the HP LoadRunner forums.

    Posted by Ankur | February 3, 2009, 3:41 pm
  3. thank you that was so clear , however i have another problem in understanding concurent users , if i have a script with 100 vuser on yahoo 1) Login, 2) Check no of unread mails 3) Logout
    and they iterate for taks no 2) twice and in the controller i edit to 500 Vuser to run conncurrently ? please confirm if the below is true :
    1- 500 concurrent user will run
    2- each with 100 vuser and it will iterate for task no 2) ( all will run as vuser squence at the script)
    my question is:
    If i use Pramaterization for vuser random/once/…etc the possibilty of use to run with multisessions that may cause conflict at DB side (if Vusers are submitting order for example)
    how can i prevent that??


    Posted by lina | August 3, 2009, 1:50 pm
  4. The explanation you have give in vice versa. For ex: in load runner script, we have two function i.e. web_concurrent_start(NULL) and web_concurrent_end(NULL). These functions perform concurrency. Its like a rendezvous point when all the URLs get loaded concurrently while in rendezvous point all vusers loaded concurrently.

    Posted by Manish | September 15, 2009, 6:02 pm
  5. @Jacintha
    Introducing lr_rendesvous create concurrency at that point – the immediate next function will be executed at single point in time (causing maximum pressure/load on DB/app/web servers. web_concurrent_start statement can be used for concurrent execution of a series of steps as Manish quoted.

    First, change in controller to simulate 500 users doesnt mean 500 concurrent users.These are 500 simultaneous users (and could be 2 or 2 overlapping/concurrent users by chance)
    User and VUser is same. Controller decides the number of VUsers to simulate and not script. If you mention 10 users_name in script and run controller with 100 (assuming multiple instances are possible) then you’re testing application with 100 Users.

    Second, having multiple iterations for various actions doesnt mean additional users. 100 VUsers and 1000000 iterations each – will simulate a load of 100 vusers only.

    Third, if you use random/once for pramaterization then provide unique data for order number/name (whatever is required to be unique) – if it is coming from server as response, you need to correlate your script.

    I hope that addresses your issues – although pretty late.


    Posted by Kamran Khan | June 1, 2010, 1:03 pm
  6. Hi,
    I am very new to loadrunner, but have decent exposure to QTP.
    I have question for loadrunner testing
    Consider that my business process is mapped in loadrunner in the form of 3 separate test scripts that require 3 different login and logoff sessions. The 3rd test script is dependant on 2nd and 2nd in turn on first and these are dependant business workflow.
    Can I schedule to run these 3 test scripts in bvelow fashion

    start testing
    Start TS 1 with vusers 10 and ramp up to 100———30 minutes duration
    Continue to run TS1 and start TS 2 with 20 vusers–20 minutes duration
    Reduce vusers for TS 1 to 10 and continue ———–5 minutes duration
    continue TS1, TS2 and start TS3 with 30 vusers—–30 minutes duration
    ramp down the vusers for all TS

    Posted by Rahul | December 21, 2010, 12:14 am
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    I’ll be more than happy if you let me know it.


    Posted by Sunny Azam | May 21, 2011, 9:17 pm
  8. Please correct blog:

    Simultaneous users have active connections to the same Web site, whereas concurrent users hit the site at exactly the same moment. Concurrent access is likely to occur at infrequent intervals. Your site may have 100 to 150 concurrent users but 1,000 to 1,500 simultaneous users.

    When load testing your application, you can simulate simultaneous users by including a random think time in your script such that not all the user threads from the load generator are firing requests at the same moment. This is useful to simulate real world situations.

    for more information(Check workload section):

    Posted by Ritesh | September 12, 2011, 2:19 pm
  9. concurrent users(5)<Simultaneous user(100) on the website

    Posted by Raman | May 16, 2013, 4:17 pm
  10. Simultaneous & Concurrent User defination is wrong. find the below correct answer.

    Simultaneous User load: The simultaneous users have the active session on the server at any
    point of time wherein each user will be executing different transactions. For example, if we say
    100 simultaneous users load, then there will be 100 active sessions opened up in the server,
    wherein each user will be performing different set of transactions – one logging in, another
    viewing reports, another navigating to the next page, etc. The simultaneous user load of a web
    site would be always greater than the concurrent user load of a web site

    Concurrent User load: The concurrent users connect to the server and perform the same
    operation at any point of time. For example, if we say 100 concurrent user load, all 100 users
    would be logging in at the same point of time, view the reports at the same point of time, etc. For
    example, an online banking web site might have 10,000 – 20,000 simultaneous user load, but
    1000 to 1500 concurrent user load.

    Posted by Veera | August 6, 2013, 8:17 pm

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