ackfoobar 10 months ago

Probably yes.

https://bugs.openjdk.org/browse/JDK-8076103

Closed with "Won't Fix".

Reply View 2 replies
lbalazscs 10 months ago

In 2015 there was no ZGC. Today ZGC (an optional garbage collector optimized for latency) guarantees that there will be no GC pauses longer than a millisecond.

Reply View 17 replies
  • survivedurcode 10 months ago

    I would check your answer. These are pauses due to time spent writing to diagnostic outputs. These are not traditional collection pauses. This affects both jstat as well as writes of GC logs. (I.e. GC log writes will block the app just the same way)

    Reply View 2 replies
    • pjmlp 10 months ago

      Which is why for anything serious one should be using Flight Recorder instead.

      Reply View 1 reply
      • funcDropShadow 10 months ago

        Or /tmp should be a tmpfs as it is on most current Linux distributions.

        Reply View 0 replies
  • esaym 10 months ago

    These modern garbage collectors are not simply free though. I got bored last year and went on a deep dive with GC params for Minecraft. For my needs I ended up with: -XX:+UseParallelGC -XX:MaxGCPauseMillis=300 -Xmx2G -Xms768M

    When flying around in spectator mode, you'd see 3 to 4 processes using 100%. Changing to more modern collectors just added more load to the system. ZGC was the worst, with 16+ processes all using 100% cpu. With the ParallelGC, yes you'll get the occasional pause but at least my laptop is not burning hot fire.

    Reply View 5 replies
    • plandis 10 months ago

      Yes no GC is free (well perhaps Epsilon comes close :)

      It’s a low pause GC so latencies, particularly tail latencies, can be more predictable and bounded. The tradeoff you make is that it uses more CPU time and memory in order to operate.

      Reply View 0 replies
    • mike_hearn 10 months ago

      Minecraft really needs generational ZGC (totally brand new) because Minecraft generates garbage at prodigious rates and non-generational GC collects less garbage per unit time.

      Reply View 0 replies
    • namibj 10 months ago

      You'll need more spare heap for ZGC.

      Reply View 1 reply
      • ackfoobar 10 months ago

        And using generational ZGC will probably lower CPU usage a lot.

        Reply View 0 replies
    • tuna74 10 months ago

      Yes, this is why GCs work so bad for 3D games since you are usually limited by memory bandwidth and latency, especially on systems with unified RAM (no seperate GPU RAM).

      Reply View 0 replies
  • kanzenryu2 10 months ago

    Sadly in many cases no; it's not magic. This nirvana is restricted to cases where there is CPU bandwidth available (e.g. some cores idle) and plenty of free RAM. When either CPU or RAM are less plentiful... hello pauses my old friend.

    Reply View 4 replies
    • sunshowers 10 months ago

      This is why memory-bound services generally use languages without mandatory GC. Tail latency is a killer.

      Rust's memory management does have some issues in practice (large synchronous drops) but they're relatively minor and easily addressed compared to mandatory GC.

      Reply View 3 replies
      • foobarchu 10 months ago

        In cases where java is unavoidable and you're working with large blocks, it is possible to sort of skirt around the gc with certain kinds of large buffers that live outside the heap.

        I've used these to great success when I had multiple long-lived gigabyte+ arrays. Without off-heap memory, these tended to really slow the gc down (to be fair, I didn't have top of the line gc algorithms because the openj9 jvm had been mandated)

        Reply View 2 replies
  • hawk_ 10 months ago

    ZGC doesn't remove safepoint requests on threads which is the root cause. "Guarantees" here are with very heavy quotes.

    Reply View 1 reply
    • funcDropShadow 10 months ago

      But it reduces the amount of safepoint requests by doing more in parallel to the working application.

      Reply View 0 replies
  • hinkley 10 months ago

    The cost of statistics gathering on a GC implementation that avoids ineffective GC activity is less affected by the cost of telemetry (no news is good news), but it is still affected.

    Reply View 0 replies