Load testing tools will report the performance of the system from the end-user perspective – i.e. how long pages take to load in the browser. This information crucial for determining if the site has a performance problem, but does not give a complete picture – it does not tell you why the site is slow. For that, you need performance data from your servers. This will allow you to, for example, correlate periods of slow response time to periods of high CPU utilization. Or find that the number of connections to the database server rises dramatically right before a flurry of errors are recorded. Or find a sudden increase in disk I/O due to a previously scheduled backup job.
Many load-testing tools have the ability to collection server-side data and integrate them effortlessly into the test reports. This can save a lot of time and effort after each test. Load Tester makes collecting server-side metrics on supported operating systems effortless – and tailors the data to make it more relevant to the context of load testing.
If your organization has monitoring systems in place, you may find that watching the metrics from those sources during the load testing can be insightful. This will also show you exactly what what to look for on a daily basis after the testing is complete and the system is live.
Chris Merrill, Chief Engineer