alt Hacker NewsI still don't get why Java is the only language that needs the heap to be carefully tuned. Like it hogs some memory at start, crashes if you go above a certain amount, and doesn't return memory to the OS when GC'd. Even Python and JS don't have those problems.
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You don't have to do anything, it just works.
But eventually someone gonna write the goddamn whole of AWS or Alibaba in the language where you have machines with TBs of heaps (yeah, you read that right), where most other managed languages would just give up instantly - and then you may have to add 2-3 parameters to make it actually run properly in these extreme conditions.
They do, but then people either work around them, or rewrite in Rust.
Java has all these knobs, because the ultimate goal is not needed to rewrite, rather fine tuning, just like when you look at the endless command line options for GCC, clang, MSVC,...
It is also a matter of implementation, Android is Java (kind of), and you also don't get push knobs unless you are a developer talking directly to a single device over ADB.
> I still don't get why Java is the only language that needs the heap to be carefully tuned.
Only tuning you should be doing is setting the heap size and algorithm (Though, size is likely enough).
> Like it hogs some memory at start, crashes if you go above a certain amount, and doesn't return memory to the OS when GC'd. Even Python and JS don't have those problems.
Unlike Python and I believe most javascript engines, the JVM uses moving garbage collectors. That's the primary reason why it hogs memory.
In these ready to return to OS languages, when something is freed or allocated they are literally calling "malloc" and "free" directly. That's why stuff tends to return back to the OS faster.
The JVM doesn't do that. When a GC runs in the JVM, the JVM picks up and moves live data to a new location. That means the JVM needs a minimum amount of free space to operate. The benefit of this is the JVM can allocate really fast, it's just a single pointer bump and a check to ensure there's enough space. It's pretty close to the same performance as the stack is in C++.
And if there's a lot of data that lives for a short period of time, the JVM frees that data very fast as well. There is little accounting that the JVM has to do to free stuff up because it's simply moving the live data.
For even the fastest allocators that python/javascript engines use, this isn't true. They have to keep track of the various allocation locations and the gaps in allocation when something is freed. And a request for allocation needs to ultimately find a location in the heap with enough room.
Java does have a memory issue, though, all objects in java are pretty bulky. This will hopefully be fixed in future versions when "value" types are added.