Analyzing Load Test Results

Article
06/26/2007

You can use the load test analyzer to view your load test data. You can analyze your load test to locate bottlenecks, identify errors, and measure improvements in your application. For more information about how to open the load test analyzer, see Accessing Load Test Results.

Load test data contains performance counter samples collected periodically from the computers-under-test. It also contains error and threshold rule violation information. For more information, see Load Test Counter Sets.

The amount of performance data collected during a load test depends on the length of the test run, the sampling interval, the number of computers under test, and the number of counters being collected. For a large load test, the amount of data collected can easily be several gigabytes.

By default, the test controller saves all the performance counter data that is collected to a database while the load test is running. Some additional data is only loaded into the database after the test is completed. For example, error details and timing details. For more information, see Load Test Results Stores.

Note

By default, timing details are not collected. To collect this data, in the Load Test Editor, under the Run Settings node, select the run setting node to change. In the Properties window, for the Timing Details Storage property, select StatisticsOnly or AllIndividualDetails.

Running versus Completed Tests

While a load test is running, a smaller set of the performance counter data is maintained in memory. You can monitor this set of data while your load test is running. While a load test is running, up to 200 samples for each performance counter are maintained. This includes 100 evenly spaced samples that span the load test’s current elapsed time, and the most recent 100 samples.

After a load test has completed, you can load the full set of data from the database. When a load test finishes, you will see the following message:

Load test '<TEST NAME>' is complete. The test data currently displayed only represents a part of the available results. Would you like to view the detailed results from the load test result store?

If you click Yes, the full set of data is loaded from the database. If you click No, the smaller set of data is still displayed. To load the full set of data later, click the View detailed results hyperlink on the load test status bar.

Note

You can drill down into any sample period that you want while you view the full set of data.

Differences between Running and Completed Tests

There are some differences in what data you can see while a load test is running and what data you can see after a load test has completed. There are also some differences in the functionality of the tools available to analyze the data.

Unique to a test that is running:

A smaller set of the data is maintained in memory.
A progress indicator specifies the time that remains.
A button on the load test toolbar is available to stop the load test.
Collapsing and scrolling modes are available on graphs.
A sample plot is displayed on the graph when the mouse hovers over a performance counter that has not been plotted.

Unique to a test that has completed:

The full set of data is available from the database.
Percentile data is available.
Min / Max lines are available on graphs.
Zooming mode is available on graphs, which enables you to analyze data that is contained within any time range.

Viewing Data in the Load Test Analyzer

When you view the results of a load test run, you can display different panes that provide you with different ways to analyze the data. To display more of the panes, click Full Screen on the View menu to maximize what is visible.

Graph View

When you view load test data, you can view the data as a graph, to see how it changes over time. To switch to graph view, click Graphs on the load test toolbar.

For more information, see Working with Graphs.

Tables View

When you view load test data, you can view the data as detailed tables. To switch to table view, click Tables on the load test toolbar.

For more information, see Working with Load Test Tables.

The Counters Pane

The counters pane displays the performance counters that have been collected during the load test. You can toggle the counters pane on and off by clicking the counters pane button on the load test toolbar.

The Summary Pane

The summary pane displays summary data from the test run. You can toggle the summary pane on and off by clicking the summary pane button on the load test toolbar.