Loadrunner vuser limit

Question

So I've read elsewhere that LoadRunner is well known to support 2-4k users easily enough, but what that didn't tell me was what sort of environment LoadRunner needed to do that. Is there any sort of guidance available on what the environment needs to be for various loads?

For example, Would a single dual-core 2.4Ghz CPU, 4GB RAM support 1,000 concurrent vUsers easily? What about if we were testing something at a larger scale (say 10,000 users) where I assume we'd need a small server farm to generate ? What would be the effect of fewer machines but with more network cards?

Answer 1

There have been tests run with loadrunner well into the several hundred thousand user ranges. You can imagine the logistical effort on the infrastructure required to run such tests.

Your question on how many users can a server support is actually quite a complex question. Just like any other piece of engineered software, each virtual user takes a slice of resources to operate from the finite pool of CPU, DISK, Network and RAM. So, simply adding more network cards doesn't buy you anything if your limiting factor is CPU for your virtual users. Each virtual user type has a base weight and then your own development and deployment models alter that weight. I have observed a single load generator that could take 1000 winsock users easily with less than 50% of all used resources and then drop to 25 users for a web application which had significantly high network data flows, lots of state management variables and the need for some disk activity related to the loading of files as part of the business process. You also don't want to max load your virtual user hosts in order to limit the possibility of test bed influences on your test results.

If you have immature loadrunner users then you can virtually guarantee you will be running less than optimal virtual user code in terms of resource utilization which could result in as few as 10% of what you should expect to run on a given host to produce load because of choices made in virtual user type, development and deployment run time settings.

I know this is not likely the answer you wanted to hear, i.e, "for your hosts you can get 5732 of virtual user type xfoo," but there is no finite answer without holding the application as a constant and the skills of the user of the tool as a constant. Then you can move from protocol to protocol and from host to host and find out how many users you can get per box.

Answer 2

Ideally each virtual user needs around 4 mb of ram memory.. so you can calculate what number your existing machine can reach up to..