I've spent the last few years researching GC for my PhD and realized that the ecosystem lacked standard tools to quantify GC CPU overhead—especially with modern concurrent collectors where pause times don't tell the whole story.

To fix this blind spot, I built a new telemetry framework into OpenJDK 26. This post walks through the CPU-memory trade-off and shows how to use the new API to measure exactly what your GC is costing you.

I'll be around and am happy to answer any questions about the post or the implementation!

Devs keep on trying to sneak in G1GC or ZGC because they hyper focus on pause time as being the only metric of value. Hopefully this new log:cpu will give us a better tool for doing GC time and computational costs. And for me, will make for a better way to argue that "it's ok that the parallel collector had a 10s pause in a 2 hour run".

It also deceived programmers into failing to manage complex lifecycles. Debugging wasted memory consumption is a huge pain.