WebDriver with PhantomJS - performance on multiple instances

[restell...@gmail.com]

Hello everyone.
My requirements are to launch at the same time, on a single machine, some website navigations (up to 6 times simultaneously).
I've done this with C# using the .NET bindings with the PhantomJSDriver.

Everything seems to work good but the execution time changes with the number of instances opened.
Like: 1 instance - 16 seconds, 3 instances - 25 seconds each, 5 instances - 40 seconds each.

The cpu/memory of the machine doesn't seems to be overloaded...
I've tried different websites, but problem always occurs...

Have you by any chance have any idea of what could be the problem?

Thank you very much

[restell...@gmail.com]

Update:

With more test, I noticed that if I execute more navigation sequentially, without close the driver,
only the firsts ones suffer a considerable slowdown...

Here's some code:

var drivers = new List<IWebDriver>();
for (int i = 0; i < 3; i++)
{
    var phantomService = new PhantomJSDriverService.CreateDefaultService();
    phantomService.Port = 9190 + i;
    drivers.Add(new PhantomJSDriver(phantomService));
}

Parallel.Invoke(
    () =>
    {
        Navigation01(drivers[0]);    //<-- slow
        Navigation01(drivers[0]);
    },
    () =>
    {
        Navigation02(drivers[1]);    //<-- slow
        Navigation02(drivers[1]);
    },
    () =>
    {
        Navigation03(drivers[2]);    //<-- slow
        Navigation03(drivers[2]);
    });

Basically I don't like the idea to manage a pool of PhantomJs instances, I'd like to open/close the driver for each navigation I made.

[Ken P]

>>Like: 1 instance - 16 seconds, 3 instances - 25 seconds each, 5 instances - 40 seconds each.

Even if your cpu/mem doesn't looked stressed, you could still be core-bound (not enough cores to service all of the threads spawned in a true parallel fashion).

In these cases I like modeling the test in JMeter when at all possible...that will give an idea of the optimal number of threads to run.