Load Testing Blog
Avoid Contention For Resources
Unless you’ve specifically designed your load test to include them, the most accurate, consistent results will come from tests that do not compete for resources with other processes – particularly sporadic, uneven processes.
If the site’s peak traffic is at 2pm and the least traffic is at 2am, it may be tempting to run your load tests at 2a. Have you checked the backup schedule with the sysadmins? If your backups run at 2:30a, you could spend hours diagnosing strange performance anomalies that could not be reproduced in a second test at 4a. Sounds obvious, right? But it happens all the … Continue reading »
Running a good load test requires getting the right people involved
If you are testing in-house, then you will (hopefully) have the opportunity to run many tests. This gives you the opportunity to shake out your testing process ahead of time and to bring individuals in as needed to look at specific problems.
If, however, you are using an outside testing resource service or will be running one big test on a production system, then it is crucial to have the right people involved in the planning and execution of the test. This list includes:
Network administrators
System developers and/or integrators
Web- and app-server administrators
Database admins
Architects
Content Experts
3rd-party services, such as your hosting company
During the load … Continue reading »
Validate the Testcases
When a website is placed under heavy load, it can fail in a wide variety of ways. The site may become unresponsive or return an HTTP status code indicating an error (500). Or it might return a web page that is mostly complete (the headers, footers and navigation are all present) but is missing a critical part that was related to the failure.
If the load test scenarios (testcases) do not validate page content well enough to catch these problems, the results could be misleading. I.e. the system could be failing but the results indicate success. In the process of helping … Continue reading »
Test Only as Accurately as Needed
In previous posts, I’ve talked a lot about the dangers of not accurately simulating the real-world usage. But there is another side to this story: obsessing too much over an accurate simulation can be very costly. There is one very important thing to understand about load testing: No matter how hard we strive to make tests accurate, they are still only an estimate.
Your load test will never match even one single hour of production usage, not even once, no matter how hard you try. Bold statement? Perhaps. Consider this: even if you could capture the exact usage of real-world customers … Continue reading »
Troubleshooting Obsolete License Error
So your license is obsolete, what exactly does that mean? By default a Load Tester license is not set to expire unless it is a temporary license. An obsolete license essentially means that the license version does not match the Load Tester version number.
When a license is mismatched, the following message appears:
As you can see on the License Key Summary, the version code is listed as 4.2, however the current version of Load Tester I have installed is 4.3.
When a license shows up as obsolete, you have two options:
Match up the license version with a downgraded version … Continue reading »
Identify and Test High-Risk Operations
As I described in my previous post on choosing test scenarios, the early tests should focus on the high-traffic scenarios. After testing and optimizing those, the next step is to identify and test the rarely-used but high-risk operations. These are operations that may have an impact on performance that is not proportional to their frequency. Even though these are not as common, they can have large impacts due to their system-wide nature and can cause sporadic performance drops during production hours that defy explanation.
Examples include:
Complex searches
Updates that touch many joined tables at once
Mass changes to data that affect many … Continue reading »
Design a Load Test that Measures What You Really Want to Know
When the first few testcases are ready, the next step is to put them together into a load test. How they are combined and executed will have a big impact on the accuracy of the test.
Testcase ratios – Make sure that each testcase is exercised in the correct ratio relative to the other testcases. For example, it is likely that many more people will be searching for products than buying them – the load configuration should reflect this ratio.
Page ratios – Re-visit the hit rate that will be exerted on each page based on the ratio of testcases and the … Continue reading »
Build Realistic Testcases
When you have identified the first group of scenarios to test, it is time to turn them into testcases, which is the term we use for the representation of the scenario in software. In it’s simplest form, a testcase is a list of pages to visit. In the simplest tools, it may simply be a list of URLs. With most tools, the testcase is a program generated by the tool and customized by the tester. More sophisticated tools, such as Load Tester, present the testcase visually.
The testcase represents not only the page … Continue reading »
Understanding the Page Grouper
One of the key capabilities of Web Performance Load Tester is the page grouper. This is one of those systems for which, the fewer people notice it, the better it is performing. Essentially the page grouper takes a long list of HTTP transactions in a test case and organizes them, using timing, and/or content and referrer analysis, into a series of logical pages.
If we do this well, we assume that the list of pages we see in a test script after a recording are the same as the logical pages an end user would witness in a browser — each … Continue reading »
Recording in Load Tester: What’s Going On?
Load Tester is designed to recognize common use patterns and transform them into working test cases with a minimum of user intervention. Our clients appreciate that Load Tester does a tremendous amount of work automatically. But, any load testing tool must be prepared to exercise the complexity of its target, and for some web applications even a simple test case can involve hundreds of variables.
This post will try to elucidate the stages of the recording process, which are, roughly:
Recording
Initial Inspection
Automatic Configuration
Manual Configuration
Replay
Validation
During the recording stage, we manually perform a use case in a web browser. Load Tester monitors our work … Continue reading »