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  <constMethodKlass>

   4:         30326        3892592  <methodKlass>

   5:          2719        3226344  <constantPoolKlass>

   6:          2450        1948704  <constantPoolCacheKlass>

   7:          2719        1869200  <instanceKlassKlass>

   8:         27599         662376  java.lang.String

   9:           836         442968  <methodDataKlass>

  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  <objArrayKlassKlass>

  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。

转自: https://blog.csdn.net/lxb_champagne/article/details/18352945