Tomcat内存分析相关方法(jmap和mat)

linux环境命令行

首先，根据进程命令，获取运行的tomcat的进程id

ps aux | grep tomcat | grep java | grep bsc

在第二列可以看到进程id

然后使用jmap可以查看内存占比：

/home/work/bsc/java/jdk-1.7-7u60/bin/jmap -heap 7840

输出的结果包括了内存各个部分的占比：

[[e-mail] logs]$ /home/work/bsc/java/jdk-1.7-7u60/bin/jmap -heap 10433
attaching to process id 10433, please wait...
debugger attached successfully.
server compiler detected.
jvm version is 24.60-b09
using parallel threads in the new generation.
using thread-local object allocation.
concurrent mark-sweep gc
heap configuration:
   minheapfreeratio = 40
   maxheapfreeratio = 70
   maxheapsize      = 8388608000 (8000.0mb)
   newsize          = 1048576000 (1000.0mb)
   maxnewsize       = 1048576000 (1000.0mb)
   oldsize          = 5439488 (5.1875mb)
   newratio         = 2
   survivorratio    = 8
   permsize         = 134217728 (128.0mb)
   maxpermsize      = 268435456 (256.0mb)
   g1heapregionsize = 0 (0.0mb)
heap usage:
new generation (eden + 1 survivor space):
   capacity = 943718400 (900.0mb)
   used     = 393328672 (375.1074523925781mb)
   free     = 550389728 (524.8925476074219mb)
   41.67860582139757% used
eden space:
   capacity = 838860800 (800.0mb)
   used     = 288471072 (275.1074523925781mb)
   free     = 550389728 (524.8925476074219mb)
   34.388431549072266% used
from space:
   capacity = 104857600 (100.0mb)
   used     = 104857600 (100.0mb)
   free     = 0 (0.0mb)
   100.0% used
to space:
   capacity = 104857600 (100.0mb)
   used     = 0 (0.0mb)
   free     = 104857600 (100.0mb)
   0.0% used
concurrent mark-sweep generation:
   capacity = 1288736768 (1229.03515625mb)
   used     = 706435104 (673.7090148925781mb)
   free     = 582301664 (555.3261413574219mb)
   54.816089797478334% used
perm generation:
   capacity = 134217728 (128.0mb)
   used     = 65034240 (62.021484375mb)
   free     = 69183488 (65.978515625mb)
   48.45428466796875% used
27139 interned strings occupying 3055832 bytes.

如上可以清楚的看到内存配置信息、年轻代（包括eden、from、to）、老年代、永久代各自的内存信息和占比。

使用eclipse的memory analysis tool工具进行详细分析

首先，使用命令将内存dump到文件：

/home/work/bsc/java/jdk-1.7-7u60/bin/jmap -dump:format=b,file=/home/work/tmp/bsc.bin 10433

mat(memory analyzer tool)工具是eclipse的一个插件，使用起来非常方便，尤其是在分析大内存的dump文件时，可以非常直观的看到各个对象在堆空间中所占用的内存大小、类实例数量、对象引用关系、利用oql对象查询，以及可以很方便的找出对象gc roots的相关信息，当然最吸引人的还是能够快速为开发人员生成内存泄露报表，方便定位问题和分析问题。

 

然后就可以查看内存中的数据，点击饼图，也可以看下占比最大的对象是什么，从而分析程序的行为。