• 【JVM】G1垃圾收集器

    目录

    G1垃圾收集器

    启动参数设置

    -XX:+UseG1GC
-XX:+PrintGCDetails
-XX:+PrintGCDateStamps
-Xloggc:../logs/gc.log
-Xms3600M
-Xmx4000M
-Xmn1800M
-XX:+UnlockExperimentalVMOptions
-XX:InitiatingHeapOccupancyPercent=40
-XX:G1NewSizePercent=16
-XX:G1MaxNewSizePercent=35


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    日志解读

    1. Young GC
    
17.132: [GC pause (G1 Evacuation Pause) (young), 0.0469581 secs]
   
   [Parallel Time: 18.7 ms, GC Workers: 8]
   	  
      [GC Worker Start (ms): Min: 17132.7, Avg: 17132.8, Max: 17132.9, Diff: 0.3]
      
      [Ext Root Scanning (ms): Min: 0.6, Avg: 1.0, Max: 2.3, Diff: 1.7, Sum: 7.8]
      
      [Update RS (ms): Min: 0.0, Avg: 0.0, Max: 0.0, Diff: 0.0, Sum: 0.0]
         [Processed Buffers: Min: 0, Avg: 0.0, Max: 0, Diff: 0, Sum: 0]
      
      [Scan RS (ms): Min: 0.0, Avg: 0.1, Max: 0.1, Diff: 0.1, Sum: 0.8]
      
      [Code Root Scanning (ms): Min: 0.0, Avg: 2.5, Max: 16.9, Diff: 16.9, Sum: 20.3]
      
      [Object Copy (ms): Min: 0.8, Avg: 14.3, Max: 16.8, Diff: 16.0, Sum: 114.4]
      
      [Termination (ms): Min: 0.0, Avg: 0.5, Max: 0.6, Diff: 0.6, Sum: 4.2]
         [Termination Attempts: Min: 1, Avg: 79.6, Max: 113, Diff: 112, Sum: 637]
      
      [GC Worker Other (ms): Min: 0.0, Avg: 0.0, Max: 0.1, Diff: 0.0, Sum: 0.3]
      
      [GC Worker Total (ms): Min: 18.4, Avg: 18.5, Max: 18.6, Diff: 0.2, Sum: 147.8]
     
      [GC Worker End (ms): Min: 17151.3, Avg: 17151.3, Max: 17151.3, Diff: 0.0]
   
   [Code Root Fixup: 0.1 ms]
   [Code Root Purge: 0.0 ms]
   
   [Clear CT: 0.5 ms]
   [Other: 27.6 ms]
   	  
      [Choose CSet: 0.0 ms]
      
      [Ref Proc: 25.9 ms]
      [Ref Enq: 0.2 ms]
      [Redirty Cards: 0.4 ms]
      
      [Humongous Register: 0.1 ms]
      [Humongous Reclaim: 0.0 ms]
      
      [Free CSet: 0.6 ms]
   
   [Eden: 1024.0M(1024.0M)->0.0B(969.0M) Survivors: 0.0B->55.0M Heap: 1024.0M(3600.0M)->54.9M(3600.0M)]
 
 [Times: user=0.22 sys=0.03, real=0.05 secs] 

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    2. 并发标记周期
    
188.769: [GC pause (G1 Evacuation Pause) (young) (initial-mark) (to-space exhausted), 0.3093628 secs]
   [Parallel Time: 280.3 ms, GC Workers: 8]
      [GC Worker Start (ms): Min: 188769.5, Avg: 188769.5, Max: 188769.5, Diff: 0.1]
      [Ext Root Scanning (ms): Min: 8.8, Avg: 17.0, Max: 68.9, Diff: 60.1, Sum: 136.1]
      [Update RS (ms): Min: 1.5, Avg: 2.1, Max: 2.4, Diff: 0.9, Sum: 16.5]
         [Processed Buffers: Min: 4, Avg: 6.0, Max: 12, Diff: 8, Sum: 48]
      [Scan RS (ms): Min: 39.3, Avg: 39.5, Max: 39.9, Diff: 0.6, Sum: 316.0]
      [Code Root Scanning (ms): Min: 0.0, Avg: 0.0, Max: 0.1, Diff: 0.1, Sum: 0.2]
      [Object Copy (ms): Min: 169.2, Avg: 221.3, Max: 229.5, Diff: 60.3, Sum: 1770.4]
      [Termination (ms): Min: 0.0, Avg: 0.0, Max: 0.0, Diff: 0.0, Sum: 0.3]
         [Termination Attempts: Min: 1, Avg: 173.4, Max: 218, Diff: 217, Sum: 1387]
      [GC Worker Other (ms): Min: 0.0, Avg: 0.0, Max: 0.0, Diff: 0.0, Sum: 0.1]
      [GC Worker Total (ms): Min: 279.9, Avg: 280.0, Max: 280.0, Diff: 0.1, Sum: 2239.6]
      [GC Worker End (ms): Min: 189049.4, Avg: 189049.4, Max: 189049.5, Diff: 0.0]
   [Code Root Fixup: 0.0 ms]
   [Code Root Purge: 0.0 ms]
   [Clear CT: 0.4 ms]
   [Other: 28.7 ms]
      [Evacuation Failure: 26.7 ms]
      [Choose CSet: 0.0 ms]
      [Ref Proc: 0.1 ms]
      [Ref Enq: 0.0 ms]
      [Redirty Cards: 0.4 ms]
      [Humongous Register: 0.1 ms]
      [Humongous Reclaim: 0.1 ms]
      [Free CSet: 0.6 ms]
   [Eden: 139.0M(2776.0M)->0.0B(2800.0M) Survivors: 24.0M->0.0B Heap: 3972.9M(4000.0M)->3965.9M(4000.0M)]
 [Times: user=0.73 sys=0.03, real=0.31 secs] 

63.229: [GC concurrent-root-region-scan-start]
63.251: [GC concurrent-root-region-scan-end, 0.0216084 secs]

63.251: [GC concurrent-mark-start]
63.522: [GC concurrent-mark-end, 0.2707228 secs]

63.522: [GC remark 63.522: [Finalize Marking, 0.0001454 secs] 63.522: [GC ref-proc, 0.0041888 secs] 63.527: [Unloading, 0.0148012 secs], 0.0200650 secs]
 [Times: user=0.17 sys=0.00, real=0.02 secs] 

63.544: [GC cleanup 481M->480M(3600M), 0.0052624 secs]
 [Times: user=0.00 sys=0.00, real=0.01 secs] 

63.550: [GC concurrent-cleanup-start]
63.550: [GC concurrent-cleanup-end, 0.0000105 secs]

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    3. Mixed GC

    并发收集阶段结束后发生；在混合垃圾收集处理的CSet不仅包括新生代的分区，还包括老年代分区（并发标记阶段标记出来的那些老年代分区）

    老年代的堆占有率达到参数 -XX：InitiatingHeapOccupancyPercent 设定的值时触发

    241.813: [GC pause (G1 Evacuation Pause) (mixed), 0.0287869 secs]
   [Parallel Time: 23.6 ms, GC Workers: 8]
      [GC Worker Start (ms): Min: 241813.0, Avg: 241813.1, Max: 241813.3, Diff: 0.3]
      [Ext Root Scanning (ms): Min: 1.9, Avg: 3.8, Max: 10.1, Diff: 8.2, Sum: 30.3]
      [Update RS (ms): Min: 0.0, Avg: 5.0, Max: 6.5, Diff: 6.5, Sum: 39.9]
         [Processed Buffers: Min: 0, Avg: 11.5, Max: 41, Diff: 41, Sum: 92]
      [Scan RS (ms): Min: 0.0, Avg: 0.9, Max: 1.2, Diff: 1.1, Sum: 7.3]
      [Code Root Scanning (ms): Min: 0.0, Avg: 0.0, Max: 0.1, Diff: 0.1, Sum: 0.3]
      [Object Copy (ms): Min: 13.1, Avg: 13.5, Max: 13.6, Diff: 0.5, Sum: 107.7]
      [Termination (ms): Min: 0.0, Avg: 0.0, Max: 0.0, Diff: 0.0, Sum: 0.1]
         [Termination Attempts: Min: 1, Avg: 28.3, Max: 40, Diff: 39, Sum: 226]
      [GC Worker Other (ms): Min: 0.0, Avg: 0.1, Max: 0.1, Diff: 0.1, Sum: 0.5]
      [GC Worker Total (ms): Min: 23.0, Avg: 23.3, Max: 23.3, Diff: 0.3, Sum: 186.1]
      [GC Worker End (ms): Min: 241836.3, Avg: 241836.4, Max: 241836.4, Diff: 0.1]
   [Code Root Fixup: 0.1 ms]
   [Code Root Purge: 0.0 ms]
   [Clear CT: 0.5 ms]
   [Other: 4.7 ms]
      [Choose CSet: 0.1 ms]
      [Ref Proc: 3.1 ms]
      [Ref Enq: 0.2 ms]
      [Redirty Cards: 0.1 ms]
      [Humongous Register: 0.1 ms]
      [Humongous Reclaim: 0.1 ms]
      [Free CSet: 0.6 ms]
   [Eden: 988.0M(988.0M)->0.0B(988.0M) Survivors: 36.0M->36.0M Heap: 2170.6M(3600.0M)->1137.8M(3600.0M)]
 [Times: user=0.22 sys=0.00, real=0.03 secs] 

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    4. Full GC

    堆内存空间不足以分配新的对象，或者元空间使用率达到设定的阈值，会触发Full GC

    
111.789: [Full GC (System.gc())  841M->629M(3600M), 1.8352739 secs]
   [Eden: 16.0M(1008.0M)->0.0B(1024.0M) Survivors: 16.0M->0.0B Heap: 841.3M(3600.0M)->629.1M(3600.0M)], [Metaspace: 236174K->236173K(1265664K)]
 [Times: user=1.94 sys=0.63, real=1.84 secs] 

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189.157: [Full GC (Allocation Failure)  3972M->757M(3600M), 1.7356564 secs]
   [Eden: 0.0B(2800.0M)->0.0B(2800.0M) Survivors: 0.0B->0.0B Heap: 3972.9M(4000.0M)->757.5M(3600.0M)], [Metaspace: 299178K->294749K(1327104K)]
 [Times: user=2.59 sys=0.03, real=1.74 secs] 

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    JVM调优实战

    设置启动参数，启动我们的java程序

    -Xverify:none
-XX:+PrintGCDetails
-XX:+PrintGCDateStamps
-Xloggc:../logs/gc.log
-Xms3600M
-Xmx4000M
-Xmn1024M
-XX:MetaspaceSize=280M
-XX:MaxMetaspaceSize=512M
-XX:+UseG1GC

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    jps -l 查看进程信息，找到进程id

    jstat -calss [pid] 查看类加载情况

    jstat -gc [pid] 查看进程gc情况

    在这里插入图片描述

    类加载时间，107.41秒，GC时间7.012秒，Young GC次数118次，较为频繁，

    修改参数配置，初始堆内存调大

    -Xmn2800M

    下面的参数配置是为了让G1收集器能够触发Mixed GC

    -XX:+UnlockExperimentalVMOptions
    -XX:InitiatingHeapOccupancyPercent=40
    -XX:G1NewSizePercent=16
    -XX:G1MaxNewSizePercent=35

    在这里插入图片描述

    Young GC次数减少，但是触发了Full GC，GC总时长还是变长了，

    
[Eden: 2617.0M(2617.0M)->0.0B(2776.0M) Survivors: 183.0M->24.0M Heap: 3940.9M(4000.0M)->3833.9M(4000.0M)]
[Eden: 139.0M(2776.0M)->0.0B(2800.0M) Survivors: 24.0M->0.0B Heap: 3972.9M(4000.0M)->3965.9M(4000.0M)]
[Eden: 7168.0K(2800.0M)->0.0B(2800.0M) Survivors: 0.0B->0.0B Heap: 3972.9M(4000.0M)->3972.9M(4000.0M)]
[Eden: 0.0B(2800.0M)->0.0B(2800.0M) Survivors: 0.0B->0.0B Heap: 3972.9M(4000.0M)->3972.9M(4000.0M)]

189.157: [Full GC (Allocation Failure)  3972M->757M(3600M), 1.7356564 secs]
   [Eden: 0.0B(2800.0M)->0.0B(2800.0M) Survivors: 0.0B->0.0B Heap: 3972.9M(4000.0M)->757.5M(3600.0M)], [Metaspace: 299178K->294749K(1327104K)]
 [Times: user=2.59 sys=0.03, real=1.74 secs] 

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    将初始堆内存适当调小一点，

    -Xmn2000M

    在这里插入图片描述

    阅读GC日志，发现触发了Full GC是因为显示调用System.gc()，

    113.168: [Full GC (System.gc())  3107M->629M(3600M), 2.0742394 secs]
   [Eden: 2440.0M(2623.0M)->0.0B(2800.0M) Survivors: 177.0M->0.0B Heap: 3107.3M(3600.0M)->629.3M(3600.0M)], [Metaspace: 234445K->234443K(1263616K)]
 [Times: user=2.80 sys=0.03, real=2.08 secs] 

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    使用 -XX:+DisableExplicitGC ，禁止显式执行System.gc()

    在这里插入图片描述

    调整后启动参数配置如下：

    
-Xverify:none
-XX:+PrintGCDetails
-XX:+PrintGCDateStamps
-Xloggc:../logs/gc.log
-Xms3600M
-Xmx4000M
-Xmn2800M
-XX:MetaspaceSize=280M
-XX:MaxMetaspaceSize=512M
-XX:+UseG1GC
-XX:+UnlockExperimentalVMOptions
-XX:InitiatingHeapOccupancyPercent=40
-XX:G1NewSizePercent=16
-XX:G1MaxNewSizePercent=35

-XX:+DisableExplicitGC

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    本节完~~

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  • 原文地址：https://blog.csdn.net/Wang_Dong_Liang/article/details/128006976