JVM.jmp

#jmap

1. `jmap -heap pid`, JVM堆信息

using thread-local object allocation.
Parallel GC with 4 thread(s)
Heap Configuration:
   MinHeapFreeRatio = 0
   MaxHeapFreeRatio = 100
   MaxHeapSize      = 2136997888 (2038.0MB)
   NewSize          = 1310720 (1.25MB)
   MaxNewSize       = 17592186044415 MB
   OldSize          = 5439488 (5.1875MB)
   NewRatio         = 2
   SurvivorRatio    = 8
   PermSize         = 21757952 (20.75MB)
   MaxPermSize      = 85983232 (82.0MB)
   G1HeapRegionSize = 0 (0.0MB)
Heap Usage:
PS Young Generation
Eden Space:
   capacity = 34078720 (32.5MB)
   used     = 3408288 (3.250396728515625MB)
   free     = 30670432 (29.249603271484375MB)
   10.001220703125% used
From Space:
   capacity = 5242880 (5.0MB)
   used     = 0 (0.0MB)
   free     = 5242880 (5.0MB)
   0.0% used
To Space:
   capacity = 5242880 (5.0MB)
   used     = 0 (0.0MB)
   free     = 5242880 (5.0MB)
   0.0% used
PS Old Generation
   capacity = 88604672 (84.5MB)
   used     = 0 (0.0MB)
   free     = 88604672 (84.5MB)
   0.0% used
PS Perm Generation
   capacity = 22020096 (21.0MB)
   used     = 2690616 (2.5659713745117188MB)
   free     = 19329480 (18.43402862548828MB)
   12.218911307198661% used
1539 interned Strings occupying 141344 bytes.

2. `jmap -histo:live pid`能夠查看當前Java進程建立的活躍對象數目和佔用內存大小。

num     #instances         #bytes  class name
----------------------------------------------
   1:          5956         767888  <methodKlass>
   2:          5956         687232  <constMethodKlass>
   3:           406         477264  <constantPoolKlass>
   4:          2661         424416  [C
   5:           369         285472  <constantPoolCacheKlass>
  96:             2             64  [Ljava.lang.Thread;
try
 140:             1             32  java.security.Permissions
 141:             1             24  java.util.concurrent.TimeUnit$4
 142:             1             24  sun.launcher.LauncherHelper
 143:             1             24  [Lsun.launcher.LauncherHelper;
 191:             1             16  java.util.zip.ZipFile$2
 192:             1             16  java.nio.Bits$1
 193:             1             16  java.lang.System$2
 194:             1             16  java.lang.Runtime
 195:             1             16  java.util.Collections$EmptySet
 196:             1             16  java.util.Collections$EmptyList
 197:             1             16  sun.misc.Launcher$Factory
Total         23841        3375688

3. `jmap -dump:format=b,file=e:\\dump.dat pid`導出dump文件，以供分析