定位JVM内存泄漏常用命令和方法

1 ./jmap -histo:live 3559 | head -30 查看大对象，不过一般前几个都是字符数组和字节数组

2 ./jmap -dump:live,format=b,file=/opt/logs/rdrslogs/dump.hprof 3559

3 启动参数一定加verbose

4 Native Memory Tracking (NMT) 是Hotspot VM用来分析VM内部内存使用情况的一个功能。我们可以利用jcmd（jdk自带）这个工具来访问NMT的数据。

5 敲命令 jmap -heap pid

using thread-local object allocation.
Garbage-First (G1) GC with 2 thread(s)

Heap Configuration:
   MinHeapFreeRatio         = 40
   MaxHeapFreeRatio         = 70
   MaxHeapSize              = 3212836864 (3064.0MB)
   NewSize                  = 1363144 (1.2999954223632812MB)
   MaxNewSize               = 1927282688 (1838.0MB)
   OldSize                  = 5452592 (5.1999969482421875MB)
   NewRatio                 = 2
   SurvivorRatio            = 8
   MetaspaceSize            = 536870912 (512.0MB)
   CompressedClassSpaceSize = 1073741824 (1024.0MB)
   MaxMetaspaceSize         = 536870912 (512.0MB)
   G1HeapRegionSize         = 1048576 (1.0MB)

Heap Usage:
G1 Heap:
   regions  = 3064
   capacity = 3212836864 (3064.0MB)
   used     = 109591032 (104.51415252685547MB)
   free     = 3103245832 (2959.4858474731445MB)
   3.41103630962322% used
G1 Young Generation:
Eden Space:
   regions  = 13
   capacity = 1352663040 (1290.0MB)
   used     = 13631488 (13.0MB)
   free     = 1339031552 (1277.0MB)
   1.0077519379844961% used
Survivor Space:
   regions  = 0
   capacity = 0 (0.0MB)
   used     = 0 (0.0MB)
   free     = 0 (0.0MB)
   0.0% used
G1 Old Generation:
   regions  = 92
   capacity = 794820608 (758.0MB)
   used     = 95959544 (91.51415252685547MB)
   free     = 698861064 (666.4858474731445MB)
   12.073107193516552% used

6 在开启了verbose的情况下敲 jmap -clstats 7984