jmap -heap返回结果分析

jmap -heap返回结果分析

using parallel threads in the new generation.
using thread-local object allocation.
Concurrent Mark-Sweep GC
Heap Configuration:
   MinHeapFreeRatio         = 40
   MaxHeapFreeRatio         = 70
   MaxHeapSize              = 4294967296 (4096.0MB)
   NewSize                  = 858980352 (819.1875MB)
   MaxNewSize               = 858980352 (819.1875MB)
   OldSize                  = 3435986944 (3276.8125MB)
   NewRatio                 = 4
   SurvivorRatio            = 8
   MetaspaceSize            = 21807104 (20.796875MB)
   CompressedClassSpaceSize = 1073741824 (1024.0MB)
   MaxMetaspaceSize         = 17592186044415 MB
   G1HeapRegionSize         = 0 (0.0MB)

Heap Usage:
新生代
New Generation (Eden + 1 Survivor Space):
   capacity = 773128192 (737.3125MB)
   used     = 95478696 (91.05558013916016MB)
   free     = 677649496 (646.2569198608398MB)
   12.349659084738175% used
Eden Space:
   capacity = 687276032 (655.4375MB)
   used     = 95478696 (91.05558013916016MB)
   free     = 591797336 (564.3819198608398MB)
   13.892336056322709% used
From Space:
   capacity = 85852160 (81.875MB)
   used     = 0 (0.0MB)
   free     = 85852160 (81.875MB)
   0.0% used
To Space:
   capacity = 85852160 (81.875MB)
   used     = 0 (0.0MB)
   free     = 85852160 (81.875MB)
   0.0% used
concurrent mark-sweep generation:
   capacity = 3435986944 (3276.8125MB)
   used     = 119572370833685648 (1.1403309901588979E11MB)
   free     = 17478152948676 MB
   3.480000732903997E9% used

根据以上数据，我们来check一些ratio：
NewRatio = 2
Eden Space capacity = 1063256064 (1014.0MB)
From Space capacity = 4718592 (4.5MB)
To Space capacity = 5242880 (5.0MB)
简单加法，New size=1014.0+4.5+5.0=1023.5MB
MaxHeapSize = 3221225472 (3072.0MB)
年轻代占比：1023.5/3072.0=1/3。
换算NewRatio的计算，老年代/新生代，结果为2