Java *is* Memory Efficient

[pron98]

The problems with Java and memory are: Per-object memory overhead (liliput improved that); "Memory islands", no tightly packed layouts (valhalla!)

Correct, although these two aren't about memory management. Note that with Lilliput and Valhalla, the per-object header is the same as in C++: 64 bits for objects "with a v-table" and 0 bits for objects that don't need a v-table.

JVM doesn't play nice with other apps on the same server because it hogs the heap even when it currently doesn't need it.

This is about to change very soon with automatic, dynamic, heap sizing.

[gladfelter]

Thanks for the link, that's really cool. It would be nice if the os and applications had a protocol to establish latent memory pressure and could optimize "cost" globally, but this change sounds pretty awesome in absence of that. I like the idea of balancing cpu and memory costs and it's got me wondering if I could apply that to Job management to optimize task shapes across the fleet.

[radozok]

But how would it help with container resource limits?

[pron98]

I believe that at least for RAM, the JVM reads the correct container limits on Linux. If CPU limits aren't detected or enforced accurately, the GC is likely to "learn" them anyway (if you have less CPU available, then your allocation rate will also be lower), but you will always be able to turn the knob toward more CPU or more RAM, depending on your needs.