java - g1 gc 中的 `Ref Enq` 实际做了什么

Question

我在我的在线hbase服务中发现了一段gc日志如下:

2018-11-08T19:12:35.907+0800: 4069334.381: [GC pause (G1 Evacuation Pause) (young)
Desired survivor size 41943040 bytes, new threshold 1 (max 1)
- age   1:   23290768 bytes,   23290768 total
, 1.9809681 secs]
   [Parallel Time: 22.6 ms, GC Workers: 13]
      [GC Worker Start (ms): Min: 4069334380.9, Avg: 4069334381.1, Max: 4069334381.2, Diff: 0.3]
      [Ext Root Scanning (ms): Min: 0.8, Avg: 1.0, Max: 1.1, Diff: 0.3, Sum: 12.8]
      [Update RS (ms): Min: 1.6, Avg: 1.8, Max: 2.0, Diff: 0.4, Sum: 23.4]
         [Processed Buffers: Min: 1, Avg: 4.4, Max: 9, Diff: 8, Sum: 57]
      [Scan RS (ms): Min: 2.2, Avg: 2.4, Max: 2.5, Diff: 0.3, Sum: 30.9]
      [Code Root Scanning (ms): Min: 0.0, Avg: 0.0, Max: 0.0, Diff: 0.0, Sum: 0.0]
      [Object Copy (ms): Min: 6.7, Avg: 7.5, Max: 17.0, Diff: 10.4, Sum: 97.9]
      [Termination (ms): Min: 0.0, Avg: 9.5, Max: 10.3, Diff: 10.3, Sum: 123.1]
         [Termination Attempts: Min: 1, Avg: 2.5, Max: 5, Diff: 4, Sum: 33]
      [GC Worker Other (ms): Min: 0.0, Avg: 0.0, Max: 0.0, Diff: 0.0, Sum: 0.3]
      [GC Worker Total (ms): Min: 22.1, Avg: 22.2, Max: 22.3, Diff: 0.3, Sum: 288.5]
      [GC Worker End (ms): Min: 4069334403.3, Avg: 4069334403.3, Max: 4069334403.3, Diff: 0.0]
   [Code Root Fixup: 0.0 ms]
   [Code Root Purge: 0.0 ms]
   [Clear CT: 0.4 ms]
   [Other: 1957.9 ms]
      [Choose CSet: 0.0 ms]
      [Ref Proc: 4.2 ms]
      [Ref Enq: 1951.7 ms]
      [Redirty Cards: 1.2 ms]
      [Humongous Register: 0.0 ms]
      [Humongous Reclaim: 0.0 ms]
      [Free CSet: 0.3 ms]
   [Eden: 592.0M(592.0M)->0.0B(592.0M) Survivors: 32.0M->32.0M Heap: 6521.8M(12.2G)->5943.3M(12.2G)]
 [Times: user=0.19 sys=0.11, real=1.98 secs]

如您所见，大部分时间都花在Ref Enq上。我可以做些什么来优化它。

Answer 1

标题的答案::有关处理引用对象所花费时间的信息显示在 Ref Proc 和 Ref Enq 阶段中。在Ref Proc阶段，G1根据引用对象特定类型的要求更新其所指对象。在 Ref Enq 中，如果发现引用对象死亡，G1 将引用对象排队到各自的引用队列中。

优化答案::如果这些阶段花费的时间太长，则考虑使用选项 -XX:+ParallelRefProcEnabled 启用这些阶段的并行化

了解更多信息 --->

https://docs.oracle.com/javase/10/gctuning/garbage-first-garbage-collector-tuning.htm#JSGCT-GUID-0BB3B742-A985-4D5E-A9C5-433A127FE0F6