一、GC日志输出参数

　　前面通过-XX:+PrintGCDetails可以对GC日志进行打印，我们就可以在控制台查看，这样虽然可以查看GC的信息，但是并不直观，可以借助于第三方的GC日志分析工具进行查看。

　　在日志打印输出涉及到的参数如下：

　　　　‐XX:+PrintGC 输出GC日志

　　　　‐XX:+PrintGCDetails 输出GC的详细日志

　　　　‐XX:+PrintGCTimeStamps 输出GC的时间戳（以基准时间的形式）

　　　　‐XX:+PrintGCDateStamps 输出GC的时间戳（以日期的形式，如 2013‐05‐04T21:53:59.234+0800）

　　　　‐XX:+PrintHeapAtGC 在进行GC的前后打印出堆的信息

　　　　‐Xloggc:../logs/gc.log 日志文件的输出路径

1、编写测试代码

package com.zn;

import java.util.ArrayList;
import java.util.List;
import java.util.Properties;
import java.util.Random;

public class GCTest {
    public static void main(String[] args) throws Exception {
        List<Object> list = new ArrayList<Object>();
        while (true) {
            int sleep = new Random().nextInt(100);
            if (System.currentTimeMillis() % 2 == 0) {
                list.clear();
            } else {
                for (int i = 0; i < 10000; i++) {
                    Properties properties = new Properties();
                    properties.put("key_" + i, "value_" + System.currentTimeMillis() + i);
                    list.add(properties);
                }
            }
            // System.out.println("list大小为：" + list.size());
            Thread.sleep(sleep);
        }
    }
}

2、设置垃圾回收

-XX:+UseG1GC
-XX:MaxGCPauseMillis=100
-Xmx256m
-XX:+PrintGCDetails
-XX:+PrintGCTimeStamps
-XX:+PrintGCDateStamps
-XX:+PrintHeapAtGC
-Xloggc:E://accp//Y2//进阶内容//JVM//GCLogs//gc.log

3、启动程序

在E://accp//Y2//进阶内容//JVM//GCLogs下生成gc.log文件

Java HotSpot(TM) 64-Bit Server VM (25.144-b01) for windows-amd64 JRE (1.8.0_144-b01), built on Jul 21 2017 21:57:33 by "java_re" with MS VC++ 10.0 (VS2010)
Memory: 4k page, physical 8293712k(2908244k free), swap 12356048k(6018612k free)
CommandLine flags: -XX:InitialHeapSize=132699392 -XX:MaxGCPauseMillis=100 -XX:MaxHeapSize=268435456 -XX:+PrintGC -XX:+PrintGCDateStamps -XX:+PrintGCDetails -XX:+PrintGCTimeStamps -XX:+PrintHeapAtGC -XX:+UseCompressedClassPointers -XX:+UseCompressedOops -XX:+UseG1GC -XX:-UseLargePagesIndividualAllocation 
{Heap before GC invocations=0 (full 0):
 garbage-first heap   total 131072K, used 6144K [0x00000000f0000000, 0x00000000f0100400, 0x0000000100000000)
  region size 1024K, 6 young (6144K), 0 survivors (0K)
 Metaspace       used 3489K, capacity 4500K, committed 4864K, reserved 1056768K
  class space    used 381K, capacity 388K, committed 512K, reserved 1048576K
2020-03-05T17:30:53.626+0800: 0.412: [GC pause (G1 Evacuation Pause) (young), 0.0607668 secs]
   [Parallel Time: 4.0 ms, GC Workers: 4]
      [GC Worker Start (ms): Min: 412.5, Avg: 413.2, Max: 415.2, Diff: 2.7]
      [Ext Root Scanning (ms): Min: 0.0, Avg: 0.3, Max: 0.4, Diff: 0.4, Sum: 1.0]
      [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: 0.0, Max: 0.0, Diff: 0.0, Sum: 0.0]
      [Code Root Scanning (ms): Min: 0.0, Avg: 0.0, Max: 0.0, Diff: 0.0, Sum: 0.0]
      [Object Copy (ms): Min: 1.1, Avg: 2.9, Max: 3.6, Diff: 2.5, Sum: 11.7]
      [Termination (ms): Min: 0.0, Avg: 0.0, Max: 0.1, Diff: 0.1, Sum: 0.2]
         [Termination Attempts: Min: 1, Avg: 1.0, Max: 1, Diff: 0, Sum: 4]
      [GC Worker Other (ms): Min: 0.0, Avg: 0.0, Max: 0.0, Diff: 0.0, Sum: 0.1]
      [GC Worker Total (ms): Min: 1.2, Avg: 3.3, Max: 3.9, Diff: 2.7, Sum: 13.0]
      [GC Worker End (ms): Min: 416.4, Avg: 416.4, Max: 416.4, Diff: 0.0]
   [Code Root Fixup: 0.0 ms]
   [Code Root Purge: 0.0 ms]
   [Clear CT: 0.0 ms]
   [Other: 56.8 ms]
      [Choose CSet: 0.0 ms]
      [Ref Proc: 0.1 ms]
      [Ref Enq: 0.0 ms]
      [Redirty Cards: 0.0 ms]
      [Humongous Register: 0.0 ms]
      [Humongous Reclaim: 0.0 ms]
      [Free CSet: 0.0 ms]
   [Eden: 6144.0K(6144.0K)->0.0B(5120.0K) Survivors: 0.0B->1024.0K Heap: 6144.0K(128.0M)->2976.0K(128.0M)]
Heap after GC invocations=1 (full 0):
 garbage-first heap   total 131072K, used 2976K [0x00000000f0000000, 0x00000000f0100400, 0x0000000100000000)
  region size 1024K, 1 young (1024K), 1 survivors (1024K)
 Metaspace       used 3489K, capacity 4500K, committed 4864K, reserved 1056768K
  class space    used 381K, capacity 388K, committed 512K, reserved 1048576K
}
 [Times: user=0.05 sys=0.00, real=0.06 secs] 
{Heap before GC invocations=1 (full 0):
 garbage-first heap   total 131072K, used 8096K [0x00000000f0000000, 0x00000000f0100400, 0x0000000100000000)
  region size 1024K, 6 young (6144K), 1 survivors (1024K)
 Metaspace       used 3489K, capacity 4500K, committed 4864K, reserved 1056768K
  class space    used 381K, capacity 388K, committed 512K, reserved 1048576K
2020-03-05T17:30:53.824+0800: 0.554: [GC pause (G1 Evacuation Pause) (young), 0.0028500 secs]
   [Parallel Time: 2.6 ms, GC Workers: 4]
      [GC Worker Start (ms): Min: 553.6, Avg: 553.6, Max: 553.7, Diff: 0.1]
      [Ext Root Scanning (ms): Min: 0.1, Avg: 0.2, Max: 0.3, Diff: 0.2, Sum: 0.7]
      [Update RS (ms): Min: 0.0, Avg: 0.0, Max: 0.0, Diff: 0.0, Sum: 0.0]
         [Processed Buffers: Min: 0, Avg: 1.0, Max: 2, Diff: 2, Sum: 4]
      [Scan RS (ms): Min: 0.0, Avg: 0.0, Max: 0.0, Diff: 0.0, Sum: 0.0]
      [Code Root Scanning (ms): Min: 0.0, Avg: 0.0, Max: 0.0, Diff: 0.0, Sum: 0.0]
      [Object Copy (ms): Min: 2.3, Avg: 2.4, Max: 2.4, Diff: 0.1, Sum: 9.5]
      [Termination (ms): Min: 0.0, Avg: 0.0, Max: 0.0, Diff: 0.0, Sum: 0.0]
         [Termination Attempts: Min: 1, Avg: 2.5, Max: 4, Diff: 3, Sum: 10]
      [GC Worker Other (ms): Min: 0.0, Avg: 0.0, Max: 0.0, Diff: 0.0, Sum: 0.0]
      [GC Worker Total (ms): Min: 2.5, Avg: 2.6, Max: 2.6, Diff: 0.1, Sum: 10.3]
      [GC Worker End (ms): Min: 556.2, Avg: 556.2, Max: 556.2, Diff: 0.0]
   [Code Root Fixup: 0.0 ms]
   [Code Root Purge: 0.0 ms]
   [Clear CT: 0.0 ms]
   [Other: 0.2 ms]
      [Choose CSet: 0.0 ms]
      [Ref Proc: 0.1 ms]
      [Ref Enq: 0.0 ms]
      [Redirty Cards: 0.0 ms]
      [Humongous Register: 0.0 ms]
      [Humongous Reclaim: 0.0 ms]
      [Free CSet: 0.0 ms]
   [Eden: 5120.0K(5120.0K)->0.0B(9216.0K) Survivors: 1024.0K->1024.0K Heap: 8096.0K(128.0M)->6077.0K(128.0M)]
Heap after GC invocations=2 (full 0):
 garbage-first heap   total 131072K, used 6077K [0x00000000f0000000, 0x00000000f0100400, 0x0000000100000000)
  region size 1024K, 1 young (1024K), 1 survivors (1024K)
 Metaspace       used 3489K, capacity 4500K, committed 4864K, reserved 1056768K
  class space    used 381K, capacity 388K, committed 512K, reserved 1048576K
}
 [Times: user=0.06 sys=0.00, real=0.00 secs] 
{Heap before GC invocations=2 (full 0):
 garbage-first heap   total 131072K, used 15293K [0x00000000f0000000, 0x00000000f0100400, 0x0000000100000000)
  region size 1024K, 10 young (10240K), 1 survivors (1024K)
 Metaspace       used 3489K, capacity 4500K, committed 4864K, reserved 1056768K
  class space    used 381K, capacity 388K, committed 512K, reserved 1048576K
2020-03-05T17:30:54.019+0800: 0.749: [GC pause (G1 Evacuation Pause) (young), 0.0025736 secs]
   [Parallel Time: 2.4 ms, GC Workers: 4]
      [GC Worker Start (ms): Min: 749.1, Avg: 749.2, Max: 749.3, Diff: 0.2]
      [Ext Root Scanning (ms): Min: 0.0, Avg: 0.1, Max: 0.2, Diff: 0.2, Sum: 0.5]
      [Update RS (ms): Min: 0.1, Avg: 0.3, Max: 0.5, Diff: 0.4, Sum: 1.3]
         [Processed Buffers: Min: 1, Avg: 1.5, Max: 3, Diff: 2, Sum: 6]
      [Scan RS (ms): Min: 0.0, Avg: 0.0, Max: 0.0, Diff: 0.0, Sum: 0.0]
      [Code Root Scanning (ms): Min: 0.0, Avg: 0.0, Max: 0.0, Diff: 0.0, Sum: 0.0]
      [Object Copy (ms): Min: 1.3, Avg: 1.7, Max: 2.0, Diff: 0.7, Sum: 6.6]
      [Termination (ms): Min: 0.0, Avg: 0.2, Max: 0.7, Diff: 0.7, Sum: 0.7]
         [Termination Attempts: Min: 1, Avg: 2.3, Max: 5, Diff: 4, Sum: 9]
      [GC Worker Other (ms): Min: 0.0, Avg: 0.0, Max: 0.0, Diff: 0.0, Sum: 0.0]
      [GC Worker Total (ms): Min: 2.2, Avg: 2.3, Max: 2.4, Diff: 0.2, Sum: 9.3]
      [GC Worker End (ms): Min: 751.5, Avg: 751.5, Max: 751.5, Diff: 0.0]
   [Code Root Fixup: 0.0 ms]
   [Code Root Purge: 0.0 ms]
   [Clear CT: 0.0 ms]
   [Other: 0.2 ms]
      [Choose CSet: 0.0 ms]
      [Ref Proc: 0.1 ms]
      [Ref Enq: 0.0 ms]
      [Redirty Cards: 0.0 ms]
      [Humongous Register: 0.0 ms]
      [Humongous Reclaim: 0.0 ms]
      [Free CSet: 0.0 ms]
   [Eden: 9216.0K(9216.0K)->0.0B(74.0M) Survivors: 1024.0K->2048.0K Heap: 14.9M(128.0M)->8698.0K(128.0M)]
Heap after GC invocations=3 (full 0):
 garbage-first heap   total 131072K, used 8698K [0x00000000f0000000, 0x00000000f0100400, 0x0000000100000000)
  region size 1024K, 2 young (2048K), 2 survivors (2048K)
 Metaspace       used 3489K, capacity 4500K, committed 4864K, reserved 1056768K
  class space    used 381K, capacity 388K, committed 512K, reserved 1048576K
}
 [Times: user=0.00 sys=0.00, real=0.00 secs] 
{Heap before GC invocations=3 (full 0):
 garbage-first heap   total 131072K, used 84474K [0x00000000f0000000, 0x00000000f0100400, 0x0000000100000000)
  region size 1024K, 76 young (77824K), 2 survivors (2048K)
 Metaspace       used 3995K, capacity 4572K, committed 4864K, reserved 1056768K
  class space    used 440K, capacity 460K, committed 512K, reserved 1048576K
#####以下省略#####