In the real world, web traffic often occurs in localized spikes. Let’s assume that we are creating a load testing script for an insurance quote. The user logs into the system, makes some selections and then finally clicks a button to calculate the insurance quote. This can be modeled quite easily by recording a load testing script using the vPerformer Builder and then generating a large load of perhaps 500 concurrent virtual users. In this scenario even though all the load testing scripts are running concurrently, each script would not be performing the same step. In other words, one user could be logging in, another could be making a selection, a third one could be waiting, a fourth one could be obtaining the quote.
There are many situations, however, where a very large number of users are attempting the exact same task simultaneously. For example we could have a situation where a large number of users could be attempting to simultaneously obtain a quote. This would result in a significantly larger load on the server.
vPerformer can model this scenario using a capability called a sync point. A sync point makes virtual users wait during load test execution for a specified number of virtual users to arrive at a certain point in the script, so that they can perform a task simultaneously. A sync point placed in your script would ensure that a specified number of virtual users pause until they reach the same task. At that point they would all execute the tasks together.
SyncPoints can be added to your load testing scripts graphically or they can be inserted as a JavaScript function into your text scripts. To insert graphically select the menu item Edit > Insert Function. A function selection dialog box will pop up. Under Utility functions select “Sync Point” and click OK. A function parameters dialog will now pop up. Set the name and the number of virtual users and click OK. To insert into a text script, insert a line that looks something like ‘UtilSyncPoint(“mysyncpoint”, 500);’. This would insert a sync point called ‘mysyncpoint’ with 500 virtual users. This should be inserted just before the part that you wish to have simultaneously executed.
Sync points allow you to model a phenomenon in your scripts that often occurs in the real world. Sync point logic will not occur in a script unless it is specifically specified. Sync points can make your load testing scripts more realistic and are a valuable tool that should be used when needed.
