7 ms·

I'm not sure what "solved" would mean for GC. Can't there always be improvements in maintainability, pause duration, correctness, throughput etc. Many dimension

I'm not sure what "solved" would mean for GC. Can't there always be improvements in maintainability, pause duration, correctness, throughput etc. Many dimensions to continually improve on. Unless someone comes up with a no pause, no compute power no code fully correct GC?

kanzenryu2 4y ago
Java already has that GC, it's called Epsilon https://blogs.oracle.com/javamagazine/post/epsilon-the-jdks-do-nothing-garbage-collector https://blogs.oracle.com/javamagazine/post/epsilon-the-jdks-...
- Alifatisk 4y ago
  Epsilon doesn't GC at all?
  - deleted 4y ago
    [deleted]
  - kaba0 4y ago
    I think it was a tongue in cheek reply, as it is indeed a no-code, no-pause, no-compute power GC that does eventually reclaim the garbage (at process exit).
    - Alifatisk 4y ago
      Correct me if I am wrong but does it really GC at all if you receive an OutOfMemoryError?
      - kaba0 4y ago
        It’s meant for short lived apps where you simply wouldn’t get OOM either way. I don’t know about an objective definition for what a GC is, one I quite like is “gives the illusion of infinite memory”, based on that it isn’t a GC. But there are also conservative GCs, RCs, etc, that fail different definitions also (leaving behind circular dependencies, having false positives, in reverse order), like in case of many things in CS, there isn’t an objective definition.
        Alifatisk 4y ago
        Thank you for the explanation, I think I get it now!
tsimionescu 4y ago
Theoretically someone could perhaps one day discover the theoretically optimal GC algorithm, and someone else could write the TeX of GCs using that algorithm, and then perhaps we'd have the final GC. Extremely unlikely that such an algorithm exists of course, and even if it did, looking at sorting will quickly suggests that improvements will keep being found even if the best asymptotic complexity had been achieved.
mike_hearn 4y ago
There are some dimensions yes, but I do wonder if GC research is starting to approach the point of being "solved" well enough that we'll see a drop in investment. Not yet, clearly, but approaching that territory. If you look at the very latest JVMs you have three GCs which a spread over throughput-optimized (parallel), a middle ground jack of all trades (g1), and latency-optimized (zgc). They're a lot more self configuring in the past, so no matter what needs your app has it's usually just one CLI switch to get something fairly optimal. But ZGC is going generational, at which point it will have significantly higher throughput than before. Also, all the JVM GCs can handle massive heaps these days (like, terabyte scale). So at that point the choice might become even simpler: just use ZGC all the time unless you can tolerate higher pauses and want to reclaim some CPU for the app, in which case go with parallel. And in many cases the right tradeoff between latency and performance could be inferred automatically from the frameworks and libraries that are on the classpath, meaning that for most apps even needing to make that choice could go away. If you have a GC that doesn't pause, can handle terabyte sized heaps, has great throughput, is largely or completely self-configuring, is portable, open source, supports dozens of languages and has clean code, there are really very few metrics left to optimize after that. It seems like HotSpot is nearly there, especially when combined with GraalVM for language support.
- _a_a_a_ 4y ago
  > If you have a GC that doesn't pause, can handle terabyte sized heaps, has great throughput, is largely or completely self-configuring, is portable, open source, supports dozens of languages and has clean code Yeah. If.
  - mike_hearn 4y ago
    That's basically ZGC Generational + GraalVM. So, code that's available now albeit you'd have to compile it from version control (graalvm stable releases don't support zgc yet, released zgc isn't generational yet). Give it another year or so and that'll be shipping out of the box in ordinary JVMs.
    - 4y ago
ignoramous 4y ago
> Unless someone comes up with a no pause, no compute power no code fully correct GC? Functional programming languages can be: https://www.reddit.com/r/haskell/comments/d5d13i https://www.reddit.com/r/haskell/comments/d5d13i / https://archive.is/4iyaG https://archive.is/4iyaG

kanzenryu2 4y ago

Java already has that GC, it's called Epsilon https://blogs.oracle.com/javamagazine/post/epsilon-the-jdks-do-nothing-garbage-collector https://blogs.oracle.com/javamagazine/post/epsilon-the-jdks-...

Alifatisk 4y ago
Epsilon doesn't GC at all?
- deleted 4y ago
  [deleted]
- kaba0 4y ago
  I think it was a tongue in cheek reply, as it is indeed a no-code, no-pause, no-compute power GC that does eventually reclaim the garbage (at process exit).
  - Alifatisk 4y ago
    Correct me if I am wrong but does it really GC at all if you receive an OutOfMemoryError?
    - kaba0 4y ago
      It’s meant for short lived apps where you simply wouldn’t get OOM either way. I don’t know about an objective definition for what a GC is, one I quite like is “gives the illusion of infinite memory”, based on that it isn’t a GC. But there are also conservative GCs, RCs, etc, that fail different definitions also (leaving behind circular dependencies, having false positives, in reverse order), like in case of many things in CS, there isn’t an objective definition.
      - Alifatisk 4y ago
        Thank you for the explanation, I think I get it now!

tsimionescu 4y ago

Theoretically someone could perhaps one day discover the theoretically optimal GC algorithm, and someone else could write the TeX of GCs using that algorithm, and then perhaps we'd have the final GC. Extremely unlikely that such an algorithm exists of course, and even if it did, looking at sorting will quickly suggests that improvements will keep being found even if the best asymptotic complexity had been achieved.

mike_hearn 4y ago

There are some dimensions yes, but I do wonder if GC research is starting to approach the point of being "solved" well enough that we'll see a drop in investment. Not yet, clearly, but approaching that territory. If you look at the very latest JVMs you have three GCs which a spread over throughput-optimized (parallel), a middle ground jack of all trades (g1), and latency-optimized (zgc). They're a lot more self configuring in the past, so no matter what needs your app has it's usually just one CLI switch to get something fairly optimal. But ZGC is going generational, at which point it will have significantly higher throughput than before. Also, all the JVM GCs can handle massive heaps these days (like, terabyte scale). So at that point the choice might become even simpler: just use ZGC all the time unless you can tolerate higher pauses and want to reclaim some CPU for the app, in which case go with parallel. And in many cases the right tradeoff between latency and performance could be inferred automatically from the frameworks and libraries that are on the classpath, meaning that for most apps even needing to make that choice could go away. If you have a GC that doesn't pause, can handle terabyte sized heaps, has great throughput, is largely or completely self-configuring, is portable, open source, supports dozens of languages and has clean code, there are really very few metrics left to optimize after that. It seems like HotSpot is nearly there, especially when combined with GraalVM for language support.

_a_a_a_ 4y ago
> If you have a GC that doesn't pause, can handle terabyte sized heaps, has great throughput, is largely or completely self-configuring, is portable, open source, supports dozens of languages and has clean code Yeah. If.
- mike_hearn 4y ago
  That's basically ZGC Generational + GraalVM. So, code that's available now albeit you'd have to compile it from version control (graalvm stable releases don't support zgc yet, released zgc isn't generational yet). Give it another year or so and that'll be shipping out of the box in ordinary JVMs.
  - 4y ago

ignoramous 4y ago

> Unless someone comes up with a no pause, no compute power no code fully correct GC? Functional programming languages can be: https://www.reddit.com/r/haskell/comments/d5d13i https://www.reddit.com/r/haskell/comments/d5d13i / https://archive.is/4iyaG https://archive.is/4iyaG