How to explain growing Worker Threads in JBoss

I recently got engaged with a client who ran an increasing load test against their load-balanced application. I got engaged because they had a phenomenon they couldn’t explain – here is an excerpt of the email:

We have a jBoss application with mySQL that runs stable in a load testing environment with let’s say 20 threads. At one point this suddenly changes and jBoss uses up to 100 threads for handling requests (or whatever the configured max number of threads in jBoss might be) – until now we have not been able to pinpoint what causes this issue

I requested their collected performance metrics to take a quick look at it.

What caused this increase in JBoss worker threads under load?
What caused this increase in JBoss worker threads under load?

>>> Read the full analysis on the Dynatrace Community Portal.

Andreas Grabner has 20+ years of experience as a software developer, tester and architect and is an advocate for high-performing cloud scale applications. He is a regular contributor to the DevOps community, a frequent speaker at technology conferences and regularly publishes articles on blog.dynatrace.com. You can follow him on Twitter: @grabnerandi