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0 pointsthrowaway8943453y ago0 comments

Historically Java has traded long pause times for fast allocations, although I'm of the impression that it has recently found a way to have its cake and eat it.

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klodolph3y ago

Java has been tunable for a long time. Periodically, the recommended tuning changes, or new GC algorithms become available, etc. But it has long been possible to get short pause times with various combinations of choosing the right algorithm and writing your program the right way.

I think what really throws people off here is that getting good performance out of a Java application involves some skills which are alien to C++ programmers, and vice versa. You take an experienced C++ programmer and drop them into a Java codebase, they may have a very poor sense of what is expensive and what is cheap. Vice versa… experienced Java programmers don’t do well in C++ either.

The result is that you have precious few people with any significant, real-world experience fixing performance issues in both languages.

throwaway894345OP3y ago

Agreed, but usually tuning for short pause times involves trading off throughput or allocation performance. But at the end of the day, if you aren't allocating a bunch of garbage in the first place, then you don't need to be as concerned about the costs of allocating or cleaning up the garbage. I wish Go did more to make allocations explicit so they could be more easily recognized and avoided; I dislike Java's approach of making allocations even more implicit/idiomatic while trying to fix the cost problem in the runtime (although I admire the ambition).

SpaghettiCthulu3y ago

Parallel garbage collection in Java has been a thing for a long time. With the right tuning you might have very infrequent STW GCs, even in a game as allocation-heavy as Minecraft.

lazide3y ago

What do you consider a ‘long’ pause time?

I’ve had no issues with Java 17+ under heavy allocation/garbage collection (data encryption pipeline I haven’t tuned to reuse buffers yet), and it’s pause times are on the order of a handful of milliseconds, without meaningful tuning. I think it’s doing something like a GB/s of garbage collection.

And the jvm in question is doing a LOT more than just this, so it’s coping with millions of allocated objects at the same time.

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