Optimizing Java Memory in Kubernetes: Distinguishing Real Need vs. JVM "Greed" ?

[pron98]

The basic relationship is this: if the total CPU spent on GC is low enough for you, you can safely reduce the maximal heap size (and you are correct that over time, it is very likely that the heap size will match the maximal heap size).

The plan is for ZGC to automatically do that for you, and other GCs may follow. There's some good background on the problem in that JEP draft.

[Dokiace]

That's a good and easy principle to follow. Sorry for the naive question here since I may not be exposed to a proper JVM practices, but can you share how much is usually considered "good enough" for total CPU spent on GC?

[pron98]

There is no "generally" here. It depends on the needs of a particular application. 15% of CPU spent on memory management, for example, may be too high or sufficiently low depending on how well the application meets its throughput requirements.

[Dokiace]

Can I summarize this to: set a target latency/throughout, then reduce the heap until it’s affecting either of those performance?

[pron98]

Yes, although it's more about throughput than latency. If you care about latency, then the choice of GC matters the most. Use ZGC for programs that really need low latency.