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Explained: Virtual User Days, ("a day in the life of a virtual user")

‎03-09-2009 10:24 PM - edited ‎09-25-2015 02:49 PM

In the complex world of LoadRunner licensing we have a mechanism that allows you to have a special pool of virtual user licenses that are called Virtual User Days.  The textbook description of a Virtual User Day (a.k.a. VUD) is:


Virtual User Days are the licensing mechanism that allows Virtual Users to be executed in an unlimited number of runs against a single AUT within a single 24-hour period of time.



As you can see, that description isn’t very clear about describing how the VUD licenses actually get implemented in the LoadRunner Controller.  I’ve answered a few emails over the last few months to describe this, so I thought it might be good to share the answers and explanations here.  Virtual User Days are sold in a quantity of Virtual Users that can be executed within a 24-hour period, where once the vuser license is consumed in the first test run it can continue to be used for multiple test runs for the next 24-hours. 


For instance, the same 1000 VUDs can be used for executing tests as follows:


- unlimited test runs that run a maximum of 100 virtual users…for 10 days

- unlimited test runs that run a maximum of 500 virtual users…for 2 days

- unlimited test runs that run a maximum of 1000 virtual users…for 1 day


Keep in mind, that the 24-hour timer starts from the first time you run a test for that day.  You can request that HP Support give you a specific time-of-day to start your testing, like 9 AM.  The proper understanding here is that VUDs are only decremented from the pool when the vuser thread first runs and it will only decrement more vusers from the pool if:


A. It is 24-hours later.


B. Another test run needs more vusers than have already been decremented in the last 24 hours.



    • Customer runs test #1 for 1000 virtual users for 4 hours  (1000 VUDs are decremented from the pool)

    • Customer runs test #2 for 1500 virtual users for 2 hours (500 more VUDs are decremented from the pool)

    • Customer runs test #3 for 400 virtual users for 6 hours (0 VUDs are decremented from the pool)

    • Customer goes to bed after a 12 hour day (while they are dreaming about advanced LoadRunner correlation…VUDs expire at 12:00am)

    • Customer wakes up and runs test #4 for 300 virtual users for 2 hours (300 VUDs are decremented from the pool)

For a real customer there was some confusion about how the VUDs get used, or “activated” was the language they used.  The hypothetical situation is that they had 500 Virtual User Day licenses and proposed 3 scenarios:


Scenario #1:  We activate 100 VUDs at the start of the day. We run a load test for 100 VUDs, then follow this with another load test for 100 VUDs on the same day. Our understanding is that we have used up 100 VUDs at end of the day. We have exhausted all the 100 VUDs at the end of the day. We are left with 400 unused VUDs.

Answer:  that is correct…if the second run goes to 150 virtual users, they will only have 350 VUDs remaining for the next 24-hour cycle.

Scenario #2: We activate 100 VUDs at the start of the day. We run a load test for 50 VUDs, then follow this with another load test for 50 VUDs on the same day. Our understanding is that we have used up 50 VUDs at end of the day and that there are about 50 unused VUDs. We are now left with 450 VUDs, inspite of activating 100 VUDs at the start of that day.

Answer:  that is incorrect – there is no way to “activate” a virtual user manually.  The only way to “activate” a VUD is to run a virtual user and decrement a license from the VUD pool.  So, the VUDs are decremented from the pool when they first enter the running status.  The customer’s first run in 24 hours sets the bar for VUD consumption for the 24-hour period.  They will still have 450 VUDs remaining at the end of the day.

Scenario #3: We activate 100 VUDs at the start of the day. Due to some unforeseen issue, no test runs could be initiated. Our understanding is that at the end of the day, we are left with 500 VUDs.

Answer:  that is only partially correct – again, there is no way to manually “activate” the vusers, so if they never got any vusers running then it wouldn’t decrement any VUDs from the license pool.  They would still have 500 VUDs remaining at the end of the day.

About the Author


Mark Tomlinson is a software tester and test engineer. His career began in 1992 with a comprehensive two-year test for a life-critical transportation system, a project which captured his natural aptitude for software testing, quality assurance, and test automation. That first test project sought to prevent trains from running into each other -- and Mark has metaphorically been preventing “train wrecks” for his customers for the past 20 years. He has broad experience with real-world scenario testing of large and complex systems and is regarded as a leading expert in software testing automation with a specific emphasis on performance. For the majority of Mark’s career he has worked for companies in a strategic role and used the leading products for performance testing, profiling and measurement. He has also consistently established close ties and relationships with the majory vendors who create these tools. While working as the Technology Alliance Manager at Mercury interactive in 2001, Mark was responsible for developing innovative integrations with cutting-edge partner technologies such as Microsoft .NET, SQL Server and Windows Server, IBM Webshpere, RealNetworks, Adobe Flash, and Citrix. Mark worked for 6 years at Microsoft Corporation as a performance consultant and engineer in the Microsoft Services Labs, in the Enterprise Engineering Center, and in the SQL Server labs. His efforts to foster the success of Microsoft’s top-tier Enterprise customers was focused on their early adoption of Microsoft products as part of mission-critical operations. In 2008, as the LoadRunner Product Manager at Hewlett Packard, Mark led his team in delivering leading innovations for performance testing and engineering.

on ‎03-10-2009 01:19 PM

I recently came across your blog and have been reading along. I thought I would leave my first comment. I don't know what to say except that I have enjoyed reading. Nice blog. I will keep visiting this blog very often.



on ‎03-12-2009 05:11 PM

I am trying out the Loadrunner 9.5 trial install on vista but after successfull installation, I am not able to open the internet explore or netscape with vugen..it keeps crashing...not sure why.

Independently though, both my IE and netscape browsers works just fine....I know LR does not support Firefox and google chrome but i used it anyways and experiences similar behavior.......

I tried the data execution prevention options, added both Vugen and IE latest version, netscape, but still geting similar results...it keep crashing...please help

on ‎05-01-2009 03:38 PM

Very Useful info

on ‎06-02-2009 09:59 AM

Useful information and very clearly explained.

Thanks a lot, Mark.

on ‎10-12-2009 06:19 PM

Pingback from  JDS Australia  » Understanding LoadRunner Licensing

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