Wenn G1 beschließt, gemischte Sammlungen durchzuführen, verkleinert es unseren Eden-Raum aggressiv von 10 g auf etwa 1 g.

{Heap before GC invocations=294 (full 0):
 garbage-first heap   total 20480000K, used 18304860K [0x00000002de000000, 0x00000002de804e20, 0x00000007c0000000)
  region size 8192K, 1363 young (11165696K), 11 survivors (90112K)
 Metaspace       used 37327K, capacity 37826K, committed 38096K, reserved 1083392K
  class space    used 3935K, capacity 4081K, committed 4096K, reserved 1048576K
2016-03-31T20:57:31.002+0000: 7196.427: [GC pause (G1 Evacuation Pause) (young)
Desired survivor size 717225984 bytes, new threshold 1 (max 1)
- age   1:   41346816 bytes,   41346816 total
 7196.427: [G1Ergonomics (CSet Construction) start choosing CSet, _pending_cards: 144693, predicted base time: 48.88 ms, remaining time: 951.12 ms, target pause time: 1000.00 ms]
 7196.427: [G1Ergonomics (CSet Construction) add young regions to CSet, eden: 1352 regions, survivors: 11 regions, predicted young region time: 20.72 ms]
 7196.427: [G1Ergonomics (CSet Construction) finish choosing CSet, eden: 1352 regions, survivors: 11 regions, old: 0 regions, predicted pause time: 69.60 ms, target pause time: 1000.00 ms]
 7196.494: [G1Ergonomics (Mixed GCs) start mixed GCs, reason: candidate old regions available, candidate old regions: 789 regions, reclaimable: 4703761904 bytes (22.43 %), threshold: 5.00 %]
, 0.0673540 secs]
   [Parallel Time: 60.1 ms, GC Workers: 18]
      [GC Worker Start (ms): Min: 7196427.8, Avg: 7196428.1, Max: 7196428.2, Diff: 0.4]
      [Ext Root Scanning (ms): Min: 7.3, Avg: 7.5, Max: 7.7, Diff: 0.4, Sum: 134.2]
      [Update RS (ms): Min: 28.2, Avg: 28.8, Max: 29.9, Diff: 1.7, Sum: 518.4]
         [Processed Buffers: Min: 41, Avg: 57.7, Max: 80, Diff: 39, Sum: 1039]
      [Scan RS (ms): Min: 0.1, Avg: 0.2, Max: 0.5, Diff: 0.4, Sum: 3.7]
      [Code Root Scanning (ms): Min: 0.0, Avg: 0.0, Max: 0.0, Diff: 0.0, Sum: 0.1]
      [Object Copy (ms): Min: 22.1, Avg: 23.1, Max: 23.4, Diff: 1.3, Sum: 416.2]
      [Termination (ms): Min: 0.0, Avg: 0.0, Max: 0.0, Diff: 0.0, Sum: 0.1]
         [Termination Attempts: Min: 1, Avg: 1.0, Max: 1, Diff: 0, Sum: 18]
      [GC Worker Other (ms): Min: 0.0, Avg: 0.1, Max: 0.2, Diff: 0.2, Sum: 2.5]
      [GC Worker Total (ms): Min: 59.5, Avg: 59.7, Max: 60.0, Diff: 0.5, Sum: 1075.1]
      [GC Worker End (ms): Min: 7196487.7, Avg: 7196487.8, Max: 7196487.9, Diff: 0.2]
   [Code Root Fixup: 0.2 ms]
   [Code Root Purge: 0.0 ms]
   [Clear CT: 1.9 ms]
   [Other: 5.2 ms]
      [Choose CSet: 0.0 ms]
      [Ref Proc: 0.5 ms]
      [Ref Enq: 0.0 ms]
      [Redirty Cards: 0.5 ms]
      [Humongous Register: 0.2 ms]
      [Humongous Reclaim: 0.1 ms]
      [Free CSet: 2.3 ms]
   [Eden: 10.6G(10.6G)->0.0B(848.0M) Survivors: 88.0M->152.0M Heap: 17.5G(19.5G)->7128.3M(19.5G)]
Heap after GC invocations=295 (full 0):
 garbage-first heap   total 20480000K, used 7299344K [0x00000002de000000, 0x00000002de804e20, 0x00000007c0000000)
  region size 8192K, 19 young (155648K), 19 survivors (155648K)
 Metaspace       used 37327K, capacity 37826K, committed 38096K, reserved 1083392K
  class space    used 3935K, capacity 4081K, committed 4096K, reserved 1048576K
}
 [Times: user=1.09 sys=0.00, real=0.07 secs]
2016-03-31T20:57:31.070+0000: 7196.495: Total time for which application threads were stopped: 0.0699324 seconds, Stopping threads took: 0.0003462 seconds

Dies ist, nachdem es mit 10-11 g Eden für 60 oder mehr Sammlungen ausgeführt wurde.

Hier sind die entsprechenden JVM GC-Parameter, mit denen wir arbeiten

-Xms20000m -Xmx20000m
-XX:+UseG1GC 
-XX:G1RSetUpdatingPauseTimePercent=5 
-XX:MaxGCPauseMillis=1000 
-XX:GCTimeRatio=99 
-XX:InitiatingHeapOccupancyPercent=35 
-XX:MaxTenuringThreshold=1 
-XX:G1ConcRefinementThreads=6 
-XX:ConcGCThreads=18 
-XX:ParallelGCThreads=18

-XX:+PrintGCDetails"
-XX:+PrintGCDateStamps"
-XX:+PrintHeapAtGC"
-XX:+PrintTenuringDistribution"
-XX:+PrintGCApplicationStoppedTime"
-XX:+PrintPromotionFailure"
-XX:+PrintAdaptiveSizePolicy"

GemäßSeite 55 dieser Präsentation, Eden muss in der Größe angepasst werden, damit das maximale Pausenziel den gesamten Heap ausmacht, nicht nur für die neue Generation. Warum ist der Sammler so aggressiv?

Die durchschnittlichen Pausenzeiten für junge Generationen liegen zwischen 50 und 150 ms bei einer Haufengröße von 10 g. Wenn die Darstellung korrekt ist (ich habe nichts anderes gefunden, um die Aussage zu stützen), würde ich eine Verkleinerung um die Hälfte (20 g Haufen) erwarten, nicht um das 10-fache.