Performance tuning is critical, and things can start getting hairy with one small JVM flag. JVM is subject to GC pauses, which vary in frequency and duration. During a pause, everything stops and all kinds of unexpected behaviors start. During pauses and unstable behavior where JVM gets stuck, performance is impacted. We can see the symptoms of slow response times, high CPU, and memory utilization, or the system acts normally most of the time but behaves weirdly, such as performing extremely slow transactions and disconnections.

The majority of the time, we measure the average transaction time and ignore the outliers that cause unstable behavior. Most of the time a system behaves normally, however at certain points, system responsiveness degrades. The majority of the time, the reason for this low performance is due to low awareness of GC overhead and focusing on only average response times.

When defining performance requirements, an important question we need to answer is: What are the acceptable criteria for our application related to GC pause frequency and duration? Requirements vary from application to application, so based on our application and user experience, we need to first define these criteria.