JMap -heap 命令

jmap -heap pid

使用jmap -heap pid查看進程堆內存使用情況，包括使用的GC算法、堆配置參數和各代中堆內存使用情況.

測試輸出

如下爲使用Jmap -heap命令的輸出

Attaching to process ID 152, please wait...
Debugger attached successfully.
Server compiler detected.
JVM version is 25.201-b09  //java版本號

using thread-local object allocation. 
Parallel GC with 3 thread(s) //使用的垃圾回收算法

Heap Configuration: //java堆配置
   MinHeapFreeRatio         = 0  // 最小堆使用比例
   MaxHeapFreeRatio         = 100 //最大可用比例
   MaxHeapSize              = 6442450944 (6144.0MB)//最大堆空間大小
   NewSize                  = 34603008 (33.0MB)// 新生代配置大小
   MaxNewSize               = 2147483648 (2048.0MB)//最大新生代大小
   OldSize                  = 70254592 (67.0MB)//老年代大小
   NewRatio                 = 2 //新生代比例
   SurvivorRatio            = 8 //新生代與survivor的比例
   MetaspaceSize            = 21807104 (20.796875MB)//元空間大小，替代1.8 以前的Permgen
   CompressedClassSpaceSize = 1073741824 (1024.0MB)
   MaxMetaspaceSize         = 17592186044415 MB//最大元空間大小， 調整元空間的大小需要Full GC，一般將MetaspaceSize  MaxMetaspaceSize兩個值都設置爲256M，防止FGC
   G1HeapRegionSize         = 0 (0.0MB) //設置的 G1 區域的大小

Heap Usage://堆內存實際使用情況
PS Young Generation//新生代 
Eden Space: //伊甸區
   capacity = 1717567488 (1638.0MB)//容量
   used     = 34716456 (33.108192443847656MB)//使用
   free     = 1682851032 (1604.8918075561523MB)//空閒
   2.0212571699540693% used
From Space: // survior1區
   capacity = 29884416 (28.5MB)
   used     = 29440712 (28.07685089111328MB)
   free     = 443704 (0.42314910888671875MB)
   98.515266284608% used
To Space:// survior2 區
   capacity = 70778880 (67.5MB)
   used     = 0 (0.0MB)
   free     = 70778880 (67.5MB)
   0.0% used
PS Old Generation // 永久代使用情況
   capacity = 438829056 (418.5MB)
   used     = 325158176 (310.0950012207031MB)
   free     = 113670880 (108.40499877929688MB)
   74.09677448523372% used

65969 interned Strings occupying 6849840 bytes.