Unique Usernames in LoadRunner

LoadRunner Knowledge Base article 5218 “Generating Unique Names”, posted by John Sawbridge, gives a function to generate a “unique” string [a-zA-Z] up to 20 characters long. The function accepts a string length argument and always writes the output to a parameter called {rname}. He notes “If you invoke the function successively in the same second, you will get the same name.”

Clearly this is a weak solution. As the function writes to the same parameter each time, it is not possible to use the function more than once in a LoadRunner script without overwriting your original value and if you are running a non-trivial number of concurrent Vusers or start more than one Vuser at a time, your chances of non-unique return values are high.

Fortunately, there are better and easier ways to generate unique usernames in LoadRunner.

First of all, seeding a random number generator loses much of its point if the seed is not a frequently changing value. Calling srand(time(NULL)), as the LoadRunner documentation suggests, is not useful for all situations as the time() function returns a value in seconds. A sneaky way to get a greater precision timestamp to use as a seed value is to create a date/time parameter that returns a time that includes milliseconds, and convert it to an int with atoi(). Another way to get a high-precision timestamp would be to use lr_load_dll and run a native Windows function. But why do all of this by hand when LoadRunner has a parameter type “random”, which will let you specify a min and a max value?

While it is fun to play around with random numbers, and I hope that someone got something out of the above paragraph, if you must generate a unique username, the easiest solution is just to create a data table full of them and set the “select next row” property of your file parameter to “unique”.

John, your Knowledge Base article rates “1-Very Unhelpful”.