【Java命令二】jhat

Java  /  管理员 发布于 2年前   256

jhat用于分析使用jmap dump的文件，，可以将堆中的对象以html的形式显示出来，包括对象的数量，大小等等，并支持对象查询语言。 jhat默认开启监听端口7000的HTTP服务，jhat是Java Heap Analysis Tool的缩写

1. 用法：

[hadoop@hadoop bin]$ jhat -helpUsage:  jhat [-stack <bool>] [-refs <bool>] [-port <port>] [-baseline <file>] [-debug <int>] [-version] [-h|-help] <file>-J<flag>          Pass <flag> directly to the runtime system. For  example, -J-mx512m to use a maximum heap size of 512MB-stack false:     Turn off tracking object allocation call stack.-refs false:      Turn off tracking of references to objects-port <port>:     Set the port for the HTTP server.  Defaults to 7000-exclude <file>:  Specify a file that lists data members that should  be excluded from the reachableFrom query.-baseline <file>: Specify a baseline object dump.  Objects in  both heap dumps with the same ID and same class will  be marked as not being "new".-debug <int>:     Set debug level.    0:  No debug output    1:  Debug hprof file parsing    2:  Debug hprof file parsing, no server-version          Report version number-h|-help          Print this help and exit<file>            The file to readFor a dump file that contains multiple heap dumps,you may specify which dump in the fileby appending "#<number>" to the file name, i.e. "foo.hprof#3".All boolean options default to "true"

 

2. 产生堆内存dump文件

[hadoop@hadoop bin]$ jmap -dump:file=dump.bin.002 1819Dumping heap to /home/hadoop/software/jdk1.7.0_67/bin/dump.bin.002 ...Heap dump file created

 

3. 分析堆内存dump文件

 

提示找到1040038个对象

[hadoop@hadoop bin]$ jhat dump.bin.002 Reading from dump.bin.002...Dump file created Fri Feb 27 07:53:21 EST 2015Snapshot read, resolving...Resolving 1040038 objects...Chasing references, expect 208 dots................................................................................................................................................................................................................Eliminating duplicate references................................................................................................................................................................................................................Snapshot resolved.Started HTTP server on port 7000Server is ready.

 

 

4. UI上查看对象内存使用情况：

在首页底下有如下连接

• All classes including platform
• Show all members of the rootset
• Show instance counts for all classes (including platform) ---每个类的对象个数，从高到低排序(不显示内存占用情况)
• Show instance counts for all classes (excluding platform)
• Show heap histogram --每个类的对象个数以及占用的总空间(很有用)
• Show finalizer summary --等待回收
• Execute Object Query Language (OQL) query (查询语法点击它自带的连接)