Why doesn't it use all available RAM?

You wouldn't necessarily want a single application to consume all available memory. In many cases, an app consuming 64GB of memory would indicate a memory leak or some other problematic state that should be fixed. It's rare to need to hold that much in memory at once. If applications were, by default, allowed to consume all available memory, that could cause system stability issues, which would be bad.

Java's JVM also has a relatively low default limit. I had to increase it at some point when I was creating a program that generated 50,000x30,000px images in memory because the default limit was too low.

Thanks for the explanation. Got it, I see the point now. It makes sense that the defaults are designed for the general case and system stability. I appreciate the explanation and clarification.

It is bad manners for a program to lay claim to huge amounts of memory unless it actually needs to use it.

Thanks for the explanation!

I was just curious because, in my previous company, our application was running as a single server on a VM with a fairly large amount of memory. That got me wondering why node heap don't simply use more of the available RAM.

From what I understand now, the heap is only one part of the memory usage. The process also needs RAM for off-heap buffers, runtime overhead, stack memory, native modules, request processing, network connections, and other internal operations. So even if an application only needs 1–4 GB of heap, additional memory can still be useful for smooth operation and handling load.

Is my understanding correct?

Got it. So the idea is that an application should only use the memory it actually needs, rather than reserving large amounts of RAM just because it's available. Otherwise, it could waste resources and potentially impact overall system stability. That makes sense. Thanks for clarifying.