我们在G1收集器的并发标记步骤中遇到无法解释/未知的长暂停（8秒）。
从GC-log中提取显示问题。
2014-08-07T13:42:30.552-0400: 92183.303: [GC concurrent-root-region-scan-start]
2014-08-07T13:42:30.555-0400: 92183.305: [GC concurrent-root-region-scan-end, 0.0025230 secs]
**2014-08-07T13:42:30.555-0400: 92183.305: [GC concurrent-mark-start]**
**2014-08-07T13:42:39.598-0400: 92192.348: Application time: 9.0448670 seconds**
2014-08-07T13:42:39.601-0400: 92192.351: Total time for which application threads were stopped: 0.0029740 seconds
2014-08-07T13:42:39.603-0400: 92192.353: [GC pause (G1 Evacuation Pause) (young) 92192.354: [G1Ergonomics (CSet Construction) start choosing CSet, _pending_cards: 7980, predicted base time: 28.19 ms, remaining time: 71.81 ms, target pause time: 100.00 ms
2014-08-07T13:42:30.555-0400: 92183.305是并发标记开始的时间，大约在此步骤2秒后，应用程序开始暂停，直到下一次GC暂停。
然而，GC日志声称应用程序在此窗口期间未暂停 任何帮助理解这个问题的根本原因是值得赞赏的。
我们的目标JVM：我们尝试过Java7和Java8
java version "1.7.0_04"
Java(TM) SE Runtime Environment (build 1.7.0_04-b20)
Java HotSpot(TM) 64-Bit Server VM (build 23.0-b21, mixed mode)
java version "1.8.0_11"
Java(TM) SE Runtime Environment (build 1.8.0_11-b12)
Java HotSpot(TM) 64-Bit Server VM (build 25.11-b03, mixed mode)
我们的JVM选项：
-Xms20G -Xmx20G -Xss10M -XX:PermSize=128M -XX:MaxPermSize=128M -XX:MarkStackSize=16M
-XX:+UnlockDiagnosticVMOptions -XX:+G1PrintRegionLivenessInfo -XX:+TraceGCTaskThread
-XX:+G1SummarizeConcMark -XX:+G1SummarizeRSetStats -XX:+G1TraceConcRefinement
-XX:+UseG1GC -XX:MaxGCPauseMillis=100 -XX:InitiatingHeapOccupancyPercent=65
-XX:ParallelGCThreads=24 -verbose:gc -XX:+PrintGC -XX:+PrintGCDetails
-XX:+PrintGCDateStamps -XX:+PrintAdaptiveSizePolicy -XX:+PrintTenuringDistribution
-XX:+PrintGCApplicationStoppedTime -XX:+PrintGCApplicationConcurrentTime
-Xloggc:/common/logs/ocean-partition-gc.log