3 ms·

The best real world garbage collectors are like ZGC, Shenandoah or C4 which don't pause your program at all. They are fully concurrent. Even if you go for a GC

The best real world garbage collectors are like ZGC, Shenandoah or C4 which don't pause your program at all. They are fully concurrent. Even if you go for a GC that is designed to balance throughput and latency, like G1, you can still configure what pause times it should target and those can easily be ~10-20msec if you want, with the vast majority of pauses being far less than that (less than 3 msec). "I was recently reading some blog posts of the V8 JS engine team. There is nothing to understand or not understand there" Look, if your knowledge of GC comes from reading V8 blog posts then you're proving the grandparent's point pretty nicely. You leaped from an extremely basic and remote understanding of GC to "there's nothing to understand or not understand here".

ahartmetz 4y ago
Serious questions: if these garbage collectors are so good, why aren't they widely used? My guess is that they have downsides such as low throughput, high CPU usage, high memory usage, etc... You can't import a JVM GC into V8, to stay with my example, but you can reimplement the ideas if you have quasi-infinite money like Google.
- origin_path 4y ago
  For ZGC/Shenandoah because they're new, and they're new because they're extremely hard to implement well. For C4 because it is expensive and requires kernel patches. Also there isn't a whole lot of need for them in many use cases. Web servers for example have far bigger latency problems than GC, normally. Pauseless GC was historically driven by the HFT/finance sector for that reason. Also yes, pauseless GC tends to have higher overheads than GC that pauses for longer. Whether that matters or not depends a lot on the use cases and actual size of the overheads. For example ZGC is pauseless but not yet generational. Generational ZGC when it launches will improve throughput significantly. Google haven't done pauseless GC for V8. I don't know why not because they have done one for Android. ART uses a fully concurrent collector iirc. At any rate, although you can't import a JVM GC to V8, you can run JavaScript on the JVM using GraalJS and use the GCs that way. Though I don't recall off hand if Graal supports ZGC yet. There's no deep reason why it couldn't.
  - ahartmetz 4y ago
    Thank you. I didn't know that one GC that I regularly use (as a user) - the one in Android - is so advanced these days. Interesting!
    - origin_path 4y ago
      ART is a pretty astoundingly advanced JVM which gets nearly no publicity. It's a real shame. I bet a properly supported desktop version would be quite competitive with HotSpot! https://source.android.com/devices/tech/dalvik/gc-debug#art_gc_overview https://source.android.com/devices/tech/dalvik/gc-debug#art_... It also does mixed AOT / JITC, amongst other tricks.

ahartmetz 4y ago

Serious questions: if these garbage collectors are so good, why aren't they widely used? My guess is that they have downsides such as low throughput, high CPU usage, high memory usage, etc... You can't import a JVM GC into V8, to stay with my example, but you can reimplement the ideas if you have quasi-infinite money like Google.

origin_path 4y ago
For ZGC/Shenandoah because they're new, and they're new because they're extremely hard to implement well. For C4 because it is expensive and requires kernel patches. Also there isn't a whole lot of need for them in many use cases. Web servers for example have far bigger latency problems than GC, normally. Pauseless GC was historically driven by the HFT/finance sector for that reason. Also yes, pauseless GC tends to have higher overheads than GC that pauses for longer. Whether that matters or not depends a lot on the use cases and actual size of the overheads. For example ZGC is pauseless but not yet generational. Generational ZGC when it launches will improve throughput significantly. Google haven't done pauseless GC for V8. I don't know why not because they have done one for Android. ART uses a fully concurrent collector iirc. At any rate, although you can't import a JVM GC to V8, you can run JavaScript on the JVM using GraalJS and use the GCs that way. Though I don't recall off hand if Graal supports ZGC yet. There's no deep reason why it couldn't.
- ahartmetz 4y ago
  Thank you. I didn't know that one GC that I regularly use (as a user) - the one in Android - is so advanced these days. Interesting!
  - origin_path 4y ago
    ART is a pretty astoundingly advanced JVM which gets nearly no publicity. It's a real shame. I bet a properly supported desktop version would be quite competitive with HotSpot! https://source.android.com/devices/tech/dalvik/gc-debug#art_gc_overview https://source.android.com/devices/tech/dalvik/gc-debug#art_... It also does mixed AOT / JITC, amongst other tricks.