Worked on a chart generating service in Java some 20 years ago. At that time IBM released their JVM. Upon first tests it worked perfectly and significantly fast

Worked on a chart generating service in Java some 20 years ago. At that time IBM released their JVM. Upon first tests it worked perfectly and significantly faster than Sun's JVM. After testing it further, making tens of thousands charts, we deployed it to production. However, in production it would stop misteriosly after some time. Added a lot of logging, there were no issues in our code. After a while I realized it failed somewhere after 65536 charts were made! That was pretty suspicious. There's nothing in our code that would overflow some 16-bit counter, it worked under another JVM, and crash was not a Java exception. If I remember correctly it was not even a crash at all but entire process would freeze. It turned out it was a problem with that specific IBM JVM. We created a new thread for each chart, and that JVM froze after 65536 created threads! Moral of the story, if you already test with tens of thousands requests, make sure it's at least 64k tests.