Difference between concurrent and simultaneous vuser

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Filed under: introduction 

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.

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4 Comments on Difference between concurrent and simultaneous vuser

  1. Jacintha on Fri, 16th Jan 2009 5:33 pm

    2. 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.

  2. Ankur on Tue, 3rd Feb 2009 3:41 pm

    3. 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.

  3. lina on Mon, 3rd Aug 2009 1:50 pm

    4. 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??

    thanks

  4. Manish on Tue, 15th Sep 2009 6:02 pm

    5. 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.

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