5 ms·

Garbage collecting seems to get solved in each new release of Go and Java, apparently.

rgbrenner 11y ago
Do you actually follow Go development? 1.5 is a major improvement to the GC. The only other stable release that had any change to the GC worthy of mention in the release notes was 1.3, which was a minor change. The only possible way to interpret your statement as true, would be if "get solved" meant ANY change or bug fix was applied to the GC. Which is a statement that would apply to so much code (not just the GC) that it would make the statement completely meaningless.
- AlphaSite 11y ago
  It think he means people tout every release as the final solution to their GC issues. Not officially, necessarily, but some vocal group says it.
  - rgbrenner 11y ago
    That's not true either though. Seriously go take a look at the release announcements on hackernews.
    - Alphasite_ 11y ago
      I never said it was.
- joosters 11y ago
  Yeah, I'm being unfair in naming Go & Java specifically. But these stories of 'fixing' garbage collection come up all too often. I wonder when we'll see a further GC update that trades latency for throughput... The problem seems to be that no matter how you tweak GC, you will always have a class of program that it performs terribly for (and it seems to impact a large group of programs, never just some obscure corner case). So I suspect that this latest GC tweak will have unexpected results on some other class of program, leading to another tweak, and so on...
  - stcredzero 11y ago
    The problem seems to be that no matter how you tweak GC, you will always have a class of program that it performs terribly for For casual use, most programs can treat GC like magic, but if you are doing serious work in a language with GC, then you should learn about the GC's characteristics. That bit of due diligence and up front design effort is still often going to be tons cheaper than doing the manual memory management. Reducing latency in exchange for throughput is the right decision for the vast majority of programs that will be written in Go. It was already a very attractive language for writing a multiplayer game server, so long as I didn't have very large heaps. (Even so, I can still support 150-250 players and 10's of thousands of entities.) With the "tweak," that limitation is much relaxed.
    - banachtarski 11y ago
      > That bit of due diligence and up front design effort is still often going to be tons cheaper than doing the manual memory management. Calling shenanigans. No it's not, unless the person doing the manual solution is a novice.
      - stcredzero 11y ago
        It's not the writing of manual memory management in the usual case/happy path that's the problem. It's the very occasional mistake and the debugging time involved. (Though to be fair, automated static analysis tools have taken great strides, and this is not as big a problem as it used to be.) What GC often gets you is a program that doesn't crash but instead has performance problems, but these are often more easily profiled and found and less severe than a crash. (Manual memory management isn't immune from the same performance problems in any case.) In other words, GC gets you to "Step 1 -- Get it Correct" faster so you can play with running code faster. The cost/benefit may not fit your situation. In that case, use a different tool.
      - pascal_cuoq 11y ago
        Despite the drastic page limit in the category I was submitting in, I made sure to include a paragraph about how GC enable sharing and how the only reasonable alternative when implementing a similar system in a non-GC language is a lot of gratuitous copying to solve ownership issues in http://frama-c.com/u3cat/download/CuoqICFP09.pdf http://frama-c.com/u3cat/download/CuoqICFP09.pdf (The page limit was 4. Organizers only raised it to 6 after seeing submitted papers.) I can also confirm the “bit of due diligence” part, and the fact that it's cheaper that the aggravation of not having memory management at all. In the example that I can contribute to the discussion, the due diligence amounted to two more short articles: http://cristal.inria.fr/~doligez/publications/cuoq-doligez-mlw-2008.pdf http://cristal.inria.fr/~doligez/publications/cuoq-doligez-m... and http://blog.frama-c.com/public/unmarshal.pdf http://blog.frama-c.com/public/unmarshal.pdf
- 1wd 11y ago
  What about 1.4? "The release focuses primarily on implementation work, improving the garbage collector ..." https://golang.org/doc/go1.4 https://golang.org/doc/go1.4
  - jlouis 11y ago
    1.4 focused on getting the GC ready for the changes in 1.5. First, the code was rewritten from C to Go. Second, the GC was made precise, which is a major improvement to a GC. The GC was not made truly concurrent however, and short pause times were not addressed either. These concerns are addressed in the 1.5 release. The trade-off in 1.5 is to eliminate pause times for slightly worse throughput. For the programs Go is written to handle, this trade-off is probably fine.
deleted 11y ago
[deleted]
threeseed 11y ago
The situation for Go and Java isn't comparable. Java has expanded into the big data space in recent years and underpins Hadoop, Spark, HBase, Cassandra etc where they are dealing with heap sizes up to 1TB. The previous GC algorithms are fine for smaller heaps (<32GB) but they needed something for bigger ones hence the introduction of G1GC. Go is very much just trying to get their foundation GC perfected.
- jsprogrammer 11y ago
  Is there a perfect GC? Seems it would free memory as soon as it's no longer used.
  - danieldk 11y ago
    Depends on the circumstances. If you would free memory as soon as it's no longer used, it could lead to delays when freeing a large object graph. Also, a lot of performance can be gained be re-using frequently-allocated short-lived objects' memory, rather than freeing them without special treatment.
    - strictfp 11y ago
      The biggest problem IMO is that GC is usually used in languages where it gets no free information about variable scope. GC could actually be really useful in C++ or Rust for postponing the destruction of many small objects and doing it in one big sweep instead.
      - pcwalton 11y ago
        > GC could actually be really useful in C++ or Rust for postponing the destruction of many small objects and doing it in one big sweep instead. I've seen this claim before, but I've never understood it. You could add delayed reclamation to your system malloc if it actually helped things: just replace free() with a function that adds to a free list but doesn't actually recycle the memory. That wouldn't require more than a couple of writes and a TLS lookup. I suspect that the reason why mallocs don't do this is that there's little benefit compared to just recycling the memory right away. Prompt reclamation is actually really nice for cache reasons, and adding memory blocks to a free list is what free's fast path does in the first place. Now that's not to say that GC wouldn't be useful in C++ or Rust. I think what a GC would be useful for is for lock-free data structures and long-lived structures with dynamic lifetimes, especially ones shared between threads, to eliminate reference counting traffic. But for short-lived objects, if you have any sort of mark phase, you've already lost. Fundamentally, it's really hard to beat a system that precomputes the object lifetimes at compile time—which is what manual memory management is—with a dynamic system that has to compute them at runtime.
the8472 11y ago
Newer java GCs generally aim for larger heaps or higher throughput than the previous ones while keeping pause times low. The goals are shifting. I don't even see a mention of parallelism in that PDF. There's probably a lot of room left to squeeze out performance for Go.

Do you actually follow Go development? 1.5 is a major improvement to the GC. The only other stable release that had any change to the GC worthy of mention in the release notes was 1.3, which was a minor change. The only possible way to interpret your statement as true, would be if "get solved" meant ANY change or bug fix was applied to the GC. Which is a statement that would apply to so much code (not just the GC) that it would make the statement completely meaningless.

AlphaSite 11y ago
It think he means people tout every release as the final solution to their GC issues. Not officially, necessarily, but some vocal group says it.
- rgbrenner 11y ago
  That's not true either though. Seriously go take a look at the release announcements on hackernews.
  - Alphasite_ 11y ago
    I never said it was.
joosters 11y ago
Yeah, I'm being unfair in naming Go & Java specifically. But these stories of 'fixing' garbage collection come up all too often. I wonder when we'll see a further GC update that trades latency for throughput... The problem seems to be that no matter how you tweak GC, you will always have a class of program that it performs terribly for (and it seems to impact a large group of programs, never just some obscure corner case). So I suspect that this latest GC tweak will have unexpected results on some other class of program, leading to another tweak, and so on...
- stcredzero 11y ago
  The problem seems to be that no matter how you tweak GC, you will always have a class of program that it performs terribly for For casual use, most programs can treat GC like magic, but if you are doing serious work in a language with GC, then you should learn about the GC's characteristics. That bit of due diligence and up front design effort is still often going to be tons cheaper than doing the manual memory management. Reducing latency in exchange for throughput is the right decision for the vast majority of programs that will be written in Go. It was already a very attractive language for writing a multiplayer game server, so long as I didn't have very large heaps. (Even so, I can still support 150-250 players and 10's of thousands of entities.) With the "tweak," that limitation is much relaxed.
  - banachtarski 11y ago
    > That bit of due diligence and up front design effort is still often going to be tons cheaper than doing the manual memory management. Calling shenanigans. No it's not, unless the person doing the manual solution is a novice.
    - stcredzero 11y ago
      It's not the writing of manual memory management in the usual case/happy path that's the problem. It's the very occasional mistake and the debugging time involved. (Though to be fair, automated static analysis tools have taken great strides, and this is not as big a problem as it used to be.) What GC often gets you is a program that doesn't crash but instead has performance problems, but these are often more easily profiled and found and less severe than a crash. (Manual memory management isn't immune from the same performance problems in any case.) In other words, GC gets you to "Step 1 -- Get it Correct" faster so you can play with running code faster. The cost/benefit may not fit your situation. In that case, use a different tool.
    - pascal_cuoq 11y ago
      Despite the drastic page limit in the category I was submitting in, I made sure to include a paragraph about how GC enable sharing and how the only reasonable alternative when implementing a similar system in a non-GC language is a lot of gratuitous copying to solve ownership issues in http://frama-c.com/u3cat/download/CuoqICFP09.pdf http://frama-c.com/u3cat/download/CuoqICFP09.pdf (The page limit was 4. Organizers only raised it to 6 after seeing submitted papers.) I can also confirm the “bit of due diligence” part, and the fact that it's cheaper that the aggravation of not having memory management at all. In the example that I can contribute to the discussion, the due diligence amounted to two more short articles: http://cristal.inria.fr/~doligez/publications/cuoq-doligez-mlw-2008.pdf http://cristal.inria.fr/~doligez/publications/cuoq-doligez-m... and http://blog.frama-c.com/public/unmarshal.pdf http://blog.frama-c.com/public/unmarshal.pdf
1wd 11y ago
What about 1.4? "The release focuses primarily on implementation work, improving the garbage collector ..." https://golang.org/doc/go1.4 https://golang.org/doc/go1.4
- jlouis 11y ago
  1.4 focused on getting the GC ready for the changes in 1.5. First, the code was rewritten from C to Go. Second, the GC was made precise, which is a major improvement to a GC. The GC was not made truly concurrent however, and short pause times were not addressed either. These concerns are addressed in the 1.5 release. The trade-off in 1.5 is to eliminate pause times for slightly worse throughput. For the programs Go is written to handle, this trade-off is probably fine.

deleted 11y ago

[deleted]

threeseed 11y ago

The situation for Go and Java isn't comparable. Java has expanded into the big data space in recent years and underpins Hadoop, Spark, HBase, Cassandra etc where they are dealing with heap sizes up to 1TB. The previous GC algorithms are fine for smaller heaps (<32GB) but they needed something for bigger ones hence the introduction of G1GC. Go is very much just trying to get their foundation GC perfected.

jsprogrammer 11y ago
Is there a perfect GC? Seems it would free memory as soon as it's no longer used.
- danieldk 11y ago
  Depends on the circumstances. If you would free memory as soon as it's no longer used, it could lead to delays when freeing a large object graph. Also, a lot of performance can be gained be re-using frequently-allocated short-lived objects' memory, rather than freeing them without special treatment.
  - strictfp 11y ago
    The biggest problem IMO is that GC is usually used in languages where it gets no free information about variable scope. GC could actually be really useful in C++ or Rust for postponing the destruction of many small objects and doing it in one big sweep instead.
    - pcwalton 11y ago
      > GC could actually be really useful in C++ or Rust for postponing the destruction of many small objects and doing it in one big sweep instead. I've seen this claim before, but I've never understood it. You could add delayed reclamation to your system malloc if it actually helped things: just replace free() with a function that adds to a free list but doesn't actually recycle the memory. That wouldn't require more than a couple of writes and a TLS lookup. I suspect that the reason why mallocs don't do this is that there's little benefit compared to just recycling the memory right away. Prompt reclamation is actually really nice for cache reasons, and adding memory blocks to a free list is what free's fast path does in the first place. Now that's not to say that GC wouldn't be useful in C++ or Rust. I think what a GC would be useful for is for lock-free data structures and long-lived structures with dynamic lifetimes, especially ones shared between threads, to eliminate reference counting traffic. But for short-lived objects, if you have any sort of mark phase, you've already lost. Fundamentally, it's really hard to beat a system that precomputes the object lifetimes at compile time—which is what manual memory management is—with a dynamic system that has to compute them at runtime.

the8472 11y ago

Newer java GCs generally aim for larger heaps or higher throughput than the previous ones while keeping pause times low. The goals are shifting. I don't even see a mention of parallelism in that PDF. There's probably a lot of room left to squeeze out performance for Go.