JEP 521: Generational Shenandoah

JEP 521: Generational Shenandoahopenjdk.org

FOR MORTALS : “Older GCs require tuning. Shenandoah tries to tune itself by observing how your application behaves.” . We can stop pretending that we know how to tune GC.

Shenandoah

Shenandoah is an ultra-low pause time garbage collector that reduces GC pause times by performing more garbage collection work concurrently with the running Java program. CMS and G1 both perform concurrent marking of live objects. Shenandoah adds concurrent compaction. Makes JEP 404: Generational Shenandoahofficial.

-XX:+UnlockExperimentalVMOptions no longer needed

And dedicated azul JVM no longer needed

//check gc settings
java \
  -XX:+UnlockExperimentalVMOptions \
  -XX:+UseShenandoahGC \
  -XX:ShenandoahGCMode=generational \
  -Xlog:gc \
  -version


//run app
java \
  -XX:+UseShenandoahGC \
  -XX:ShenandoahGCMode=generational \
  -Xlog:gc \
  -Xmx512m \
  -cp target/classes \
  com.wlodar.jeeps.jep404Shenandoah.GenerationalShenandoahDemo

and its learning

0.103s][info][gc] Trigger (Young): Learning 5 of 5. Free (347M) is below initial threshold (358M)
[0.103s][info][gc] GC(4) Concurrent reset (Young) 0.153ms
[0.103s][info][gc] GC(4) Pause Init Mark (Young) 0.011ms
[0.104s][info][gc] GC(4) Concurrent remembered set scanning 0.395ms
[0.104s][info][gc] GC(4) Concurrent marking roots 0.135ms
[0.105s][info][gc] GC(4) Concurrent marking (Young) 0.605ms
[0.105s][info][gc] GC(4) Pause Final Mark (Young) 0.129ms