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 time – usually because the testers don’t even know it is happening. Find out!
Events to look for:
- database re-indexing jobs
- scheduled cache/pool flushes
- backups, including backups of unrelated systems that can hog bandwidth or SAN capacity
- anything else that is scheduled for automatic execution
Put them on your load-testing calendar so you will be aware if/when they will affect your tests.
Chris Merrill, Chief Engineer