Website Load Testing Software - Web Performance, Inc.

When a performance test is run, Web Performance Trainer^TM will simulate a number of users using their browser to access your web site. You can configure the test to automatically increase the number of users, up to the limit of your license. The product can simulate up to 200 simultaneous users per machine. This may seem like a small number compared to the large number of hits reported by major sites, but it is a typical maximum number for a single server to handle while giving an acceptable response time.

Preparing the Test Machine
Running a performance test is a CPU and memory intensive operation. In order to get the most out of your test machine, and insure the most accurate statistics you should make sure there are no background processes running on your computer. While the performance test runs Web Performance Trainer 2.1 will monitor your CPU usage and make sure you don't overload your machine. When the CPU Usage/Load Average gets too high Web Performance Trainer^TM will stop adding new virtual users. Note that if your machine's CPU load is too high at the beginning of the test, no users will be added at all! At this time check your machine's CPU load average:

Configuring The Performance Test
The following screen shot shows the playback controls configured to run a test on a single business case, "Purchase Transaction", for a duration of 10 minutes, starting with 25 simulated users. The number of users will increase by 10 every 1 minutes, so that the potential number of users at the end of the test is 115. It is best to start with a low number of users and verify the correct working of your web-back end before performing more complicated tests. Also note that the number of virtual users you can simulate is limited by the speed and memory of the playback machine, so that the actual number of virtual users generated can be lower than the value in the potential field.

In order to efficiently distribute virtual user execution over the available CPU speed, it is best to start with between 1 and 50 virtual users, and to increment by no more than 25 virtual users every minute. If your test exceeds these values an error dialog will be displayed and the test will be canceled.

You will want to pick a starting number of virtual users that's at least as big as the number of business cases. The reason is each virtual is assigned only one business case to execute, so if you don't start with at least that many, all of the business cases won't be executed.

Tests can be run on either single business cases, or on "load profiles", which are groups of business cases. Select the test type by clicking on the appropriate radio button, and "Select Test" pull down menu will be populated with either business cases or load profiles you previously created. When business cases are run directly they use the following default settings:

Duration can be in units of hours, minutes, or days. The duration of the test should change depending on your testing goals. If you are just trying to get an idea of the speed of certain operations on your site, useful performance information can be gained for tests that are a few minutes long. You can then tweak parameters in scripts or machine configuration and see if it has an affect on performance. If, however, you are trying to stress your web site to see if anything breaks, you'll want to run the test over a longer period of time. While the program can be configured to run for long periods of time, this will generate a lot of data, and will slow down operation of the program.

The Virtual User column at the right side of the Configure Playback area gives the following information:

Running The Performance Test
Once the performance test is configured it can be started by clicking on the Start button. The test can be ended at any time by clicking on the Stop button.

Field:	Definition:
Start Time	The time the test was started.
Duration	The length of time the test has been running
Hits	The total number of HTTP commands that have been generated.
Hits/s	The current number of HTTP commands per second that are being generated.
KB/s	The total number of kilobytes per second that are being transferred to and from the web site. This includes all data, including HTTP Request Headers, HTTP Reply Headers, HTML content, and images.
Cases/s	The number of business cases that are being generated per second by the test.
Errors	The number of HTTP errors that were generated. This will indicate if the simulated users are able to access the web site.
Users	The current number of users being simulated.

Field: Definition:

Computer In version 2.1 only "local" is supported.

Status Indicates whether playback is occurring or not.

Active Users The number of virtual users actually running.

Est User Capacity The total number of virtual users that Web Performance Trainer^TM estimates the machine could generate. Note that the estimated number usually is inaccurate at lower load averages, so that your computer very well may be able to generate a larger number of virtual users. This is because at low load averages the estimation is not as accurate as at a high load average. Also, the response of many computers is nonlinear, so that the load average could hover at 20%, for example, and stay there while the number of virtual users climbs.

% Memory Used This measures how much of the memory allocated for internal buffers is actually in use. This number has no relation to any operating system specific information you might view using the NT Task Manager.

This value will go up and down during the performance test, but will slowly creep up towards the value of the Total Memory below when using large numbers of virtual users, or when running the performance test for a long period of time. When the program absolutely has run out of memory you will see this value quickly climb into the 90% range every 30 seconds or so. When this happen the playback may stop to prevent the program from running out of all memory and ceasing to operate.

When the figure hits about 90% of the Total Memory, you can conserve memory by deleting old performance statistics and graphs, or by starting a new file and importing the business cases to be used in further tests. See the Memory Management page for more information.

Memory Status This indicates if the program is low on internal memory buffers. It is normal for the status to be "overloaded" during operation. When this happens the internal memory buffers will be reclaimed and the status should go back to normal. If the status is continually in the "overloaded" state then the program may stop playback in order to prevent a total loss of memory.

Percentage Load The CPU utilization of the playback computer , where 100% has all of the machine cycles being used. Note that on UNIX this value is greatly affected by background processes that are blocked, so even though a process isn't taking up any CPU time, if it is stuck in a disk wait or otherwise hung your load average will be higher. Use "ps", "top" or other programs to find and stop background processes that may be increasing the system load so that the full power of the computer is available for the performance test.

Note that there is lag in getting the information from the NT operating system, so the value will not be exactly the same as the value displayed in the NT Task Manager.

Load Status This indicates how much available load capacity your computer has available. Any value over 80% is considered to be "overloaded", and your computer is working at maximum capacity.