variance strategy as the name implies, it varies the number of threads overtime.Within the specified interval the threads will increase and decrease as per the variance value, thus simulating a realistic real time load on target web-service.
How variance is calculated : its not calculated using the mathematical variance formula. its just a multiplication. (if threads = 10 and variance = 0.5 then 10 * 0.5 = 5. The threads will be incremented and decremented by 5)
For example:
Threads = 20
variance = 0.8
Strategy = variance
interval = 60
limit = 60 seconds
the above will vary the thread by 16 (because 20 * 0.8 = 16), that is the thread count will increase to 36 and decrease to 4 and end with the original 20 within the 60 seconds.
if your requirement is to start with 500 threads and hit 1000 set your variance to 2 and so on.
refrence link:
chek the third bullet - simulating different type of load - soapUI site
Book for reference:
Web Service Testing with SoapUi by Charitha kankanamge