Feb 2, 2019

Java 11: JEP 333 ZGC A Scalable Low-Latency Garbage Collector

After i found this strange "No-Op Garbage Collector", i was keen, if there are some other new GC features with Java 11.

There is another JEP with the number 333:
 If you look here, the goals are:

  • GC pause times should not exceed 10ms
  • Handle heaps ranging from relatively small (a few hundreds of megabytes) to very large (many terabytes) in size
  • No more than 15% application throughput reduction compared to using G1
  • Lay a foundation for future GC features and optimizations leveraging colored pointers and load barriers
  • Initially supported platform: Linux/x64
 Inside JEP 333 there are some numbers for the performance provided:
Below are typical GC pause times from the same benchmark. ZGC manages to stay well below the 10ms goal. Note that exact numbers can vary (both up and down, but not significantly) depending on the exact machine and setup used.
(Lower is better)
                avg: 1.091ms (+/-0.215ms)
    95th percentile: 1.380ms
    99th percentile: 1.512ms
  99.9th percentile: 1.663ms
 99.99th percentile: 1.681ms
                max: 1.681ms

                avg: 156.806ms (+/-71.126ms)
    95th percentile: 316.672ms
    99th percentile: 428.095ms
  99.9th percentile: 543.846ms
 99.99th percentile: 543.846ms
                max: 543.846ms
This looks very promising. But within the limitations you can read, that it will take some more time, until this can be used:
The initial experimental version of ZGC will not have support for class unloading. The ClassUnloading and ClassUnloadingWithConcurrentMark options will be disabled by default. Enabling them will have no effect.
Also, ZGC will initially not have support for JVMCI (i.e. Graal). An error message will be printed if the EnableJVMCI option is enabled.
These limitations will be addressed at a later stage in this project.
Nevertheless: You can use this GC with the command line argument
-XX:+UnlockExperimentalVMOptions -XX:+UseZGC
For more information take a look here: https://wiki.openjdk.java.net/display/zgc/Main

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