jmap -histo pid 输出的[C [B [I [S methodKlass constantPoolKlass含义

JMAP 输出

[hadoop@DEV logs]$ jmap -histo 24527 | head -30

 num     #instances         #bytes  class name
----------------------------------------------
   1:         31939       98883072  [C
   2:          8594        9461992  [B
   3:         30326        4256232  
   4:         30326        3892592  
   5:          2719        3226344  
   6:          2450        1948704  
   7:          2719        1869200  
   8:         27599         662376  java.lang.String
   9:           836         442968  
  10:          8215         394320  org.apache.tomcat.util.buf.ByteChunk
  11:          3012         366720  java.lang.Class
  12:         11257         360224  java.util.HashMap$Entry
  13:          3417         273360  java.lang.reflect.Method
  14:          6763         270520  java.util.TreeMap$Entry
  15:          4326         260720  [S
  16:          5410         259680  org.apache.tomcat.util.buf.MessageBytes
  17:          6410         256400  org.apache.tomcat.util.buf.CharChunk
  18:          4558         238352  [[I
  19:          3347         211512  [Ljava.lang.Object;
  20:          2144         189280  [I
  21:           276         147936  
  22:           948         142216  [Ljava.util.HashMap$Entry;
  23:          2874         137952  java.util.HashMap
  24:           621          89424  java.text.DecimalFormat
  25:          2555          81760  java.util.concurrent.ConcurrentHashMap$HashEntry
  26:           620          69440  java.util.GregorianCalendar
  27:          1052          68936  [Ljava.lang.String;

其中：

[C is a char[]
[S is a short[]
[I is a int[]
[B is a byte[]
[[I is a int[][]

上面的输出中[C对象占用Heap这么多，往往跟String有关，String其内部使用final char[]数组来保存数据的。

constMethodKlass/ methodKlass/ constantPoolKlass/ constantPoolCacheKlass/ instanceKlassKlass/ methodDataKlass

与Classloader相关，常驻与Perm区。