JVM GC 问题

【问题标题】：JVM GC problemsJVM GC 问题
【发布时间】：2015-06-01 06:15:12
【问题描述】：

在过去的几周里，我一直在为我的 Glassfish 服务器测试不同的 JVM 设置。堆（以及其他）的主要设置是：-Xms512m、-Xmx512m、-XX:NewRatio=2。我尝试了不同的 GC 设置，但在启动服务器几天后我仍然遇到长时间暂停的问题。我注意到以下内容：
1. -XX:+UseParallelGC -XX:+UseParallelOldGC - 次要 GC 大约每分钟发生一次，主要 GC 每 18 小时发生一次。小 GC 没有问题，但 5 天后大 GC 出现问题。起初主要的 GC 暂停持续了大约 100-200 毫秒，但最后一次暂停持续了 70 秒。
2. -XX:+UseConcMarkSweepGC -XX:+UseParNewGC - 和上面的差不多。次要 GC 很好，但主要 GC（不是完全）暂停变得很长。我注意到在停止世界阶段的 GC（CMS Final Remark）阶段存在高级卸载问题。
3. -XX:+UseConcMarkSweepGC -XX:+UseParNewGC 和 -XX:MaxGCPauseMillis=5000。我只测试了一天，因为第二次主要 GC 最后一次（未满）已经持续了大约 20 秒，所以我认为还有其他问题。
4. -XX:+UseG1GC, -XX:MaxGCPauseMillis=5000, -XX:+UseStringDeduplication 没有 -XX:NewRatio=2 选项 - 主要 GC（未满）每 12 小时发生一次，我已经注意到一些问题：

2015-05-31T18:25:25.145+0200: 83383.897: [GC concurrent-mark-start]
2015-05-31T18:25:35.563+0200: 83394.312: [GC concurrent-mark-end, 10.4145795 secs]
2015-05-31T18:25:35.563+0200: 83394.312: [GC remark 83394.312: [Finalize Marking, 0.0002939 secs] 83394.312: [GC ref-proc, 1.2128584 secs] 83395.525: [Unloading, 14.5180500 secs], 15.7320854 secs]
 [Times: user=0.14 sys=0.22, real=15.73 secs]

GC 备注阶段需要 15 秒，这对我来说是不可接受的。您可以看到卸载花费了大部分时间。之前使用其他GC时也出现过这种情况，所以我认为类卸载肯定有问题。

总结：所有 GC 运行一段时间都正常，但几天后问题开始出现，暂停时间很长。我不知道为什么前几天它工作得很好，然后突然结果很糟糕。我注意到较高的暂停时间是由类卸载引起的，所以我想知道是否有一些设置可以获得更好的结果。另外我想知道您推荐我使用哪种 GC？我在具有 8gb RAM、i7 处理器和 Windows 8 操作系统的 PC 上的 glassfish 服务器上运行内部 Web 应用程序。最多同时有 10 个客户端连接，但它必须有很长的正常运行时间，并且不能有很长的暂停时间（最多 5 秒）。请告诉我我还能做些什么来缩短暂停时间。

还有一个问题：在我的情况下，使用 G1GC 而不是 CMS 或 ParallelGC 有什么缺点？使用 G1GC 堆会不会太小？

编辑：在长暂停 GC 备注阶段前后的 G1GC 日志

2015-05-31T18:25:25.004+0200: 83383.755: [GC pause (G1 Evacuation Pause) (young) (initial-mark), 0.1280453 secs]
   [Parallel Time: 116.2 ms, GC Workers: 4]
      [GC Worker Start (ms): Min: 83383757.6, Avg: 83383757.7, Max: 83383757.7, Diff: 0.0]
      [Ext Root Scanning (ms): Min: 97.8, Avg: 98.3, Max: 98.5, Diff: 0.7, Sum: 393.1]
      [Update RS (ms): Min: 0.2, Avg: 4.0, Max: 14.8, Diff: 14.6, Sum: 16.1]
         [Processed Buffers: Min: 1, Avg: 6.0, Max: 16, Diff: 15, Sum: 24]
      [Scan RS (ms): Min: 0.0, Avg: 0.0, Max: 0.1, Diff: 0.1, Sum: 0.1]
      [Code Root Scanning (ms): Min: 0.0, Avg: 0.0, Max: 0.0, Diff: 0.0, Sum: 0.0]
      [Object Copy (ms): Min: 0.2, Avg: 2.5, Max: 3.7, Diff: 3.5, Sum: 10.2]
      [Termination (ms): Min: 0.0, Avg: 8.5, Max: 11.4, Diff: 11.4, Sum: 34.2]
      [GC Worker Other (ms): Min: 0.0, Avg: 0.0, Max: 0.0, Diff: 0.0, Sum: 0.0]
      [GC Worker Total (ms): Min: 113.4, Avg: 113.4, Max: 113.5, Diff: 0.0, Sum: 453.8]
      [GC Worker End (ms): Min: 83383871.1, Avg: 83383871.1, Max: 83383871.1, Diff: 0.0]
   [Code Root Fixup: 0.1 ms]
   [Code Root Purge: 0.0 ms]
   [String Dedup Fixup: 2.2 ms, GC Workers: 4]
      [Queue Fixup (ms): Min: 0.0, Avg: 0.0, Max: 0.0, Diff: 0.0, Sum: 0.0]
      [Table Fixup (ms): Min: 2.0, Avg: 2.1, Max: 2.1, Diff: 0.1, Sum: 8.3]
   [Clear CT: 0.1 ms]
   [Other: 9.5 ms]
      [Choose CSet: 0.0 ms]
      [Ref Proc: 8.8 ms]
      [Ref Enq: 0.1 ms]
      [Redirty Cards: 0.3 ms]
      [Humongous Reclaim: 0.0 ms]
      [Free CSet: 0.1 ms]
   [Eden: 215.0M(215.0M)->0.0B(215.0M) Survivors: 7168.0K->7168.0K Heap: 451.5M(512.0M)->236.6M(512.0M)]
 [Times: user=0.08 sys=0.02, real=0.13 secs] 
2015-05-31T18:25:25.129+0200: 83383.883: [GC concurrent-root-region-scan-start]
2015-05-31T18:25:25.129+0200: 83383.883: [GC concurrent-string-deduplication, 160.0B->0.0B(160.0B), avg 48.3%, 0.0000070 secs]
   [Last Exec: 0.0000070 secs, Idle: 23.1834927 secs, Blocked: 0/0.0000000 secs]
      [Inspected:               3]
         [Skipped:              0(  0.0%)]
         [Hashed:               3(100.0%)]
         [Known:                0(  0.0%)]
         [New:                  3(100.0%)    160.0B]
      [Deduplicated:            3(100.0%)    160.0B(100.0%)]
         [Young:                3(100.0%)    160.0B(100.0%)]
         [Old:                  0(  0.0%)      0.0B(  0.0%)]
   [Total Exec: 2868/0.1946124 secs, Idle: 2868/83382.9701762 secs, Blocked: 13/0.0032760 secs]
      [Inspected:          304493]
         [Skipped:              0(  0.0%)]
         [Hashed:          163708( 53.8%)]
         [Known:            44808( 14.7%)]
         [New:             259685( 85.3%)     21.9M]
      [Deduplicated:       160467( 61.8%)     10.6M( 48.3%)]
         [Young:            83546( 52.1%)   6270.6K( 57.8%)]
         [Old:              76921( 47.9%)   4571.3K( 42.2%)]
   [Table]
      [Memory Usage: 4291.8K]
      [Size: 131072, Min: 1024, Max: 16777216]
      [Entries: 133319, Load: 101.7%, Cached: 6107, Added: 142389, Removed: 9070]
      [Resize Count: 7, Shrink Threshold: 87381(66.7%), Grow Threshold: 262144(200.0%)]
      [Rehash Count: 0, Rehash Threshold: 120, Hash Seed: 0x0]
      [Age Threshold: 3]
   [Queue]
      [Dropped: 0]
2015-05-31T18:25:25.145+0200: 83383.897: [GC concurrent-root-region-scan-end, 0.0140467 secs]
2015-05-31T18:25:25.145+0200: 83383.897: [GC concurrent-mark-start]
2015-05-31T18:25:35.563+0200: 83394.312: [GC concurrent-mark-end, 10.4145795 secs]
2015-05-31T18:25:35.563+0200: 83394.312: [GC remark 83394.312: [Finalize Marking, 0.0002939 secs] 83394.312: [GC ref-proc, 1.2128584 secs] 83395.525: [Unloading, 14.5180500 secs], 15.7320854 secs]
 [Times: user=0.14 sys=0.22, real=15.73 secs] 
2015-05-31T18:25:51.288+0200: 83410.045: [GC cleanup 334M->326M(512M), 0.2836092 secs]
 [Times: user=0.00 sys=0.00, real=0.28 secs] 
2015-05-31T18:25:51.570+0200: 83410.328: [GC concurrent-cleanup-start]
2015-05-31T18:25:51.570+0200: 83410.328: [GC concurrent-cleanup-end, 0.0000669 secs]
2015-05-31T18:26:03.732+0200: 83422.482: [GC pause (G1 Evacuation Pause) (young), 0.1031257 secs]
   [Parallel Time: 91.6 ms, GC Workers: 4]
      [GC Worker Start (ms): Min: 83422481.7, Avg: 83422481.7, Max: 83422481.8, Diff: 0.0]
      [Ext Root Scanning (ms): Min: 1.3, Avg: 1.7, Max: 2.7, Diff: 1.4, Sum: 6.9]
      [Update RS (ms): Min: 0.0, Avg: 22.7, Max: 89.8, Diff: 89.8, Sum: 90.8]
         [Processed Buffers: Min: 0, Avg: 7.3, Max: 15, Diff: 15, Sum: 29]
      [Scan RS (ms): Min: 0.0, Avg: 0.0, Max: 0.1, Diff: 0.1, Sum: 0.2]
      [Code Root Scanning (ms): Min: 0.0, Avg: 0.0, Max: 0.0, Diff: 0.0, Sum: 0.0]
      [Object Copy (ms): Min: 0.5, Avg: 2.4, Max: 3.4, Diff: 2.9, Sum: 9.5]
      [Termination (ms): Min: 0.0, Avg: 64.7, Max: 86.3, Diff: 86.3, Sum: 258.9]
      [GC Worker Other (ms): Min: 0.0, Avg: 0.0, Max: 0.0, Diff: 0.0, Sum: 0.1]
      [GC Worker Total (ms): Min: 91.6, Avg: 91.6, Max: 91.6, Diff: 0.0, Sum: 366.3]
      [GC Worker End (ms): Min: 83422573.3, Avg: 83422573.3, Max: 83422573.3, Diff: 0.0]
   [Code Root Fixup: 0.1 ms]
   [Code Root Purge: 0.0 ms]
   [String Dedup Fixup: 2.1 ms, GC Workers: 4]
      [Queue Fixup (ms): Min: 0.0, Avg: 0.0, Max: 0.0, Diff: 0.0, Sum: 0.0]
      [Table Fixup (ms): Min: 1.9, Avg: 1.9, Max: 1.9, Diff: 0.1, Sum: 7.7]
   [Clear CT: 0.1 ms]
   [Other: 9.3 ms]
      [Choose CSet: 0.0 ms]
      [Ref Proc: 8.8 ms]
      [Ref Enq: 0.1 ms]
      [Redirty Cards: 0.0 ms]
      [Humongous Reclaim: 0.0 ms]
      [Free CSet: 0.1 ms]
   [Eden: 215.0M(215.0M)->0.0B(19.0M) Survivors: 7168.0K->6144.0K Heap: 443.6M(512.0M)->228.2M(512.0M)]
 [Times: user=0.30 sys=0.01, real=0.10 secs] 
2015-05-31T18:26:03.848+0200: 83422.597: [GC concurrent-string-deduplication, 160.0B->0.0B(160.0B), avg 48.3%, 0.0123951 secs]
   [Last Exec: 0.0123951 secs, Idle: 38.7017788 secs, Blocked: 0/0.0000000 secs]
      [Inspected:               3]
         [Skipped:              0(  0.0%)]
         [Hashed:               3(100.0%)]
         [Known:                0(  0.0%)]
         [New:                  3(100.0%)    160.0B]
      [Deduplicated:            3(100.0%)    160.0B(100.0%)]
         [Young:                3(100.0%)    160.0B(100.0%)]
         [Old:                  0(  0.0%)      0.0B(  0.0%)]
   [Total Exec: 2869/0.2070075 secs, Idle: 2869/83421.6719550 secs, Blocked: 13/0.0032760 secs]
      [Inspected:          304496]
         [Skipped:              0(  0.0%)]
         [Hashed:          163711( 53.8%)]
         [Known:            44808( 14.7%)]
         [New:             259688( 85.3%)     21.9M]
      [Deduplicated:       160470( 61.8%)     10.6M( 48.3%)]
         [Young:            83549( 52.1%)   6270.8K( 57.8%)]
         [Old:              76921( 47.9%)   4571.3K( 42.2%)]
   [Table]
      [Memory Usage: 2565.5K]
      [Size: 65536, Min: 1024, Max: 16777216]
      [Entries: 81061, Load: 123.7%, Cached: 6553, Added: 142396, Removed: 61335]
      [Resize Count: 8, Shrink Threshold: 43690(66.7%), Grow Threshold: 131072(200.0%)]
      [Rehash Count: 0, Rehash Threshold: 120, Hash Seed: 0x0]
      [Age Threshold: 3]
   [Queue]
      [Dropped: 0]
2015-05-31T18:26:05.769+0200: 83424.518: [GC pause (G1 Evacuation Pause) (mixed), 0.2232916 secs]
   [Parallel Time: 216.7 ms, GC Workers: 4]
      [GC Worker Start (ms): Min: 83424518.3, Avg: 83424518.3, Max: 83424518.3, Diff: 0.0]
      [Ext Root Scanning (ms): Min: 1.2, Avg: 1.6, Max: 2.6, Diff: 1.4, Sum: 6.5]
      [Update RS (ms): Min: 0.0, Avg: 0.3, Max: 0.4, Diff: 0.4, Sum: 1.2]
         [Processed Buffers: Min: 0, Avg: 4.3, Max: 7, Diff: 7, Sum: 17]
      [Scan RS (ms): Min: 56.1, Avg: 102.3, Max: 144.4, Diff: 88.3, Sum: 409.2]
      [Code Root Scanning (ms): Min: 0.0, Avg: 0.1, Max: 0.2, Diff: 0.2, Sum: 0.3]
      [Object Copy (ms): Min: 50.4, Avg: 97.6, Max: 157.7, Diff: 107.2, Sum: 390.2]
      [Termination (ms): Min: 0.0, Avg: 14.8, Max: 19.8, Diff: 19.8, Sum: 59.1]
      [GC Worker Other (ms): Min: 0.0, Avg: 0.0, Max: 0.0, Diff: 0.0, Sum: 0.1]
      [GC Worker Total (ms): Min: 216.6, Avg: 216.6, Max: 216.6, Diff: 0.0, Sum: 866.5]
      [GC Worker End (ms): Min: 83424734.9, Avg: 83424734.9, Max: 83424734.9, Diff: 0.0]
   [Code Root Fixup: 0.1 ms]
   [Code Root Purge: 0.0 ms]
   [String Dedup Fixup: 1.5 ms, GC Workers: 4]
      [Queue Fixup (ms): Min: 0.0, Avg: 0.0, Max: 0.0, Diff: 0.0, Sum: 0.0]
      [Table Fixup (ms): Min: 1.4, Avg: 1.4, Max: 1.4, Diff: 0.0, Sum: 5.6]
   [Clear CT: 0.2 ms]
   [Other: 4.8 ms]
      [Choose CSet: 0.0 ms]
      [Ref Proc: 0.9 ms]
      [Ref Enq: 0.0 ms]
      [Redirty Cards: 0.2 ms]
      [Humongous Reclaim: 0.0 ms]
      [Free CSet: 0.2 ms]
   [Eden: 19.0M(19.0M)->0.0B(21.0M) Survivors: 6144.0K->4096.0K Heap: 247.2M(512.0M)->175.2M(512.0M)]
 [Times: user=0.09 sys=0.00, real=0.22 secs] 
2015-05-31T18:26:05.992+0200: 83424.742: [GC concurrent-string-deduplication, 640.0B->152.0B(488.0B), avg 48.3%, 0.0000246 secs]
   [Last Exec: 0.0000246 secs, Idle: 2.1442834 secs, Blocked: 0/0.0000000 secs]
      [Inspected:               6]
         [Skipped:              0(  0.0%)]
         [Hashed:               5( 83.3%)]
         [Known:                0(  0.0%)]
         [New:                  6(100.0%)    640.0B]
      [Deduplicated:            5( 83.3%)    488.0B( 76.3%)]
         [Young:                5(100.0%)    488.0B(100.0%)]
         [Old:                  0(  0.0%)      0.0B(  0.0%)]
   [Total Exec: 2870/0.2070321 secs, Idle: 2870/83423.8162384 secs, Blocked: 13/0.0032760 secs]
      [Inspected:          304502]
         [Skipped:              0(  0.0%)]
         [Hashed:          163716( 53.8%)]
         [Known:            44808( 14.7%)]
         [New:             259694( 85.3%)     21.9M]
      [Deduplicated:       160475( 61.8%)     10.6M( 48.3%)]
         [Young:            83554( 52.1%)   6271.2K( 57.8%)]
         [Old:              76921( 47.9%)   4571.3K( 42.2%)]
   [Table]
      [Memory Usage: 2564.6K]
      [Size: 65536, Min: 1024, Max: 16777216]
      [Entries: 81026, Load: 123.6%, Cached: 6553, Added: 142397, Removed: 61371]
      [Resize Count: 8, Shrink Threshold: 43690(66.7%), Grow Threshold: 131072(200.0%)]
      [Rehash Count: 0, Rehash Threshold: 120, Hash Seed: 0x0]
      [Age Threshold: 3]
   [Queue]
      [Dropped: 0]
2015-05-31T18:26:08.157+0200: 83426.906: [GC pause (G1 Evacuation Pause) (mixed), 0.6216666 secs]
   [Parallel Time: 618.5 ms, GC Workers: 4]
      [GC Worker Start (ms): Min: 83426906.5, Avg: 83426906.5, Max: 83426906.5, Diff: 0.0]
      [Ext Root Scanning (ms): Min: 0.3, Avg: 8.0, Max: 15.7, Diff: 15.3, Sum: 31.9]
      [Update RS (ms): Min: 0.0, Avg: 4.5, Max: 8.5, Diff: 8.5, Sum: 17.9]
         [Processed Buffers: Min: 0, Avg: 7.0, Max: 18, Diff: 18, Sum: 28]
      [Scan RS (ms): Min: 13.4, Avg: 28.4, Max: 65.2, Diff: 51.8, Sum: 113.7]
      [Code Root Scanning (ms): Min: 0.0, Avg: 0.0, Max: 0.1, Diff: 0.1, Sum: 0.2]
      [Object Copy (ms): Min: 532.6, Avg: 577.3, Max: 604.5, Diff: 71.9, Sum: 2309.1]
      [Termination (ms): Min: 0.0, Avg: 0.2, Max: 0.3, Diff: 0.3, Sum: 0.7]
      [GC Worker Other (ms): Min: 0.0, Avg: 0.0, Max: 0.0, Diff: 0.0, Sum: 0.1]
      [GC Worker Total (ms): Min: 618.4, Avg: 618.4, Max: 618.4, Diff: 0.0, Sum: 2473.6]
      [GC Worker End (ms): Min: 83427524.9, Avg: 83427524.9, Max: 83427524.9, Diff: 0.0]
   [Code Root Fixup: 0.1 ms]
   [Code Root Purge: 0.0 ms]
   [String Dedup Fixup: 1.3 ms, GC Workers: 4]
      [Queue Fixup (ms): Min: 0.0, Avg: 0.0, Max: 0.0, Diff: 0.0, Sum: 0.0]
      [Table Fixup (ms): Min: 1.2, Avg: 1.2, Max: 1.3, Diff: 0.1, Sum: 4.9]
   [Clear CT: 0.1 ms]
   [Other: 1.6 ms]
      [Choose CSet: 0.0 ms]
      [Ref Proc: 1.0 ms]
      [Ref Enq: 0.0 ms]
      [Redirty Cards: 0.0 ms]
      [Humongous Reclaim: 0.0 ms]
      [Free CSet: 0.2 ms]
   [Eden: 21.0M(21.0M)->0.0B(21.0M) Survivors: 4096.0K->4096.0K Heap: 196.2M(512.0M)->129.4M(512.0M)]
 [Times: user=0.08 sys=0.02, real=0.62 secs]

编辑：几个小时后的结果：

有很多页面/秒和页面输入/秒以及页面错误。这是正常的吗？我在哪里可以设置只为 JVM 监控页面/秒和页面输入/秒（我只发现页面错误）？

【问题讨论】：

  • 您将最大堆大小 (xmx) 设置为初始大小(xms) (512)。为什么不增加呢？ . i7 有足够的核心。所以 CMS 或 g1gc 应该可以正常工作（并且默认选择）。
  • 我不想使用太多内存，因为这台 PC 上运行着其他应用程序（不是 glassfish）。我认为 512m 的堆大小对于这个应用程序来说已经足够了。如果我将堆大小增加到 1024m，主要和次要 GC 会发生得更少，但暂停时间会相同甚至更高，或者我的想法不对？
  • 随着堆的增加，暂停时间会增加，但 GC 的频率会减少。我认为这是一个安全的赌注。你应该尝试增加堆并检查结果
  • 是的，但是我有暂停时间而不是频率的问题 - 如果暂停时间会更短（
  • 如果您正在运行 Java 8，请查看此处 [JDK8 的长时间类卸载暂停](blogs.oracle.com/poonam/entry/long_class_unloading_pauses_with)

标签： java garbage-collection glassfish jvm


【解决方案1】：

我猜你找错了树 - 我怀疑垃圾收集不是你的问题......

您只运行了一个 512 MiB 的堆 - 对我来说，一个大小为 1 或 2 秒的堆的长时间停顿。巨大的 (32 GiB) 堆可能会在几毫秒内出现重大暂停。

我预计问题实际上出在您的服务器上 - 您提到的其他应用程序正在使用足够的内存来将您的 Java 进程（将比堆大 50% 左右）推送到交换/虚拟内存中- 或者您正在虚拟化环境中运行您的应用程序（可能存在内存过度使用/内存膨胀问题）。

作为一个非常粗略的指标，任何 GC 算法都应该能够每秒处理 100 MiB 的堆 - 因此，如果您看到比这更糟的情况，请在其他地方寻找问题的原因。

在这种情况下，我认为 GC 是症状，而不是问题。

【讨论】：

  • 感谢您的回答。你能指出我如何检查Java进程是否被推入交换/虚拟内存或者我是否有内存膨胀问题？您如何解释前几天一切正常，突然 GC 暂停时间显着增加（glassfish 旁边的相同应用程序一直在运行）？
  • 见serverfault.com/questions/74822/…你的服务器是物理的还是虚拟的？
  • 这是物理服务器。
  • 好的，那么我的建议是使用 Windows 监控工具来构建该服务器上随时间推移发生的情况（内存使用情况、分页、计划进程等）。在您的 8 GiB 中，其中 2 个可能会被操作系统窃取，因此只需要一些行为不端的程序就会给您带来问题......
  • 好的，我会检查的。谢谢。
【解决方案2】：

[时间：user=0.14 sys=0.22, real=15.73 secs]

这意味着它花费了比实际 CPU 时间更多的 wall-time GC。您尝试过的所有 GC 都是多线程的并且纯粹受 CPU 限制，这意味着它们通常会消耗更多的 CPU 时间而不是 wall time 所消耗的时间。

有两个可能的原因会改变这种情况

  • 资源不足，堆的一部分被换出或其他进程占用 CPU。正如 @Mikaveli 建议的那样，使用操作系统监控工具来获取更多信息。
  • 某些东西会阻止 VM 在几秒钟内到达安全点。您可以通过-XX:+PrintSafepointStatistics -XX:PrintSafepointStatisticsCount=1 进行检查

此外，由于它发生在使用 -XX:-ClassUnloadingWithConcurrentMark 的备注暂停期间可能会解决它，但我想它只会将问题转移到常规 GC。

也许使用-XX:+TraceClassUnloading 跟踪它实际尝试卸载的数量会很有用。像 glassfish 这样的应用程序容器可能会做一些奇怪的事情，导致很多类堆积起来。

编辑：对于监控，您主要需要关注可用物理内存（减去缓存）、CPU 负载、页面输入/输出/错误。理想情况下在进程级别监控分页，因为它不关心 JVM 是否有另一个进程正在等待磁盘。

至于 CMS 与 G1：这可能与您的问题无关。

【讨论】：

  • 好的，SubOptimal 评论怎么样 (blogs.oracle.com/poonam/entry/long_class_unloading_pauses_with) - 这也值得尝试，因为我有完全相同的问题 - 卸载需要 14.5180500 秒
  • 你没有使用大页面。 Afaik 在 Windows 上，您首先必须编辑一些注册表策略以完全允许大页面分配。在链接的文章中，根本原因是内存分页到磁盘（IO），正如我已经解释的那样。使用大页面只是在它们的特定设置中起作用，因为它将它们与堆的其余部分一起固定到内存中。
  • 好的，我将监控这些设置并将其包含在 JVM 中（除了 -XX:-ClassUnloadingWithConcurrentMark，如果监控中没有任何显示，我将在稍后包含它）。谢谢。
  • 您好，请您解释一下：如果我使用-XX:-ClassUnloadingWithConcurrentMark，那么在remark阶段不会发生卸载，什么时候会发生？我在某个地方读到了完整 GC 期间的内容，但是如果从未激活完整 GC 怎么办？卸载是否可能永远不会发生并且我会遇到一些内存不足异常或类似问题？我一直在到处寻找答案，但我还没有找到。如果您对 ClassUnloadingWithConcurrentMark 有更多了解，请帮助我。
  • 它将在耗尽类的元空间之前执行一次完整的 GC。
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