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 Arch: generic
 Software: JDK 8
 Date: 21 November 2013
 SectDesc: Troubleshooting Tools
 Title: jhat.1

 jhat 1 "21 November 2013" "JDK 8" "Troubleshooting Tools"
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 NAME 
jhat - Analyzes the Java heap. This command is experimental and unsupported.

 SYNOPSIS 
 

jhat [ options ] heap-dump-file 

 

 
options
The command-line options. See Options.

 
heap-dump-file
Java binary heap dump file to be browsed. For a dump file that contains multiple heap dumps, you can specify which dump in the file by appending \f3#<number> to the file name, for example, \f3myfile.hprof#3.

 DESCRIPTION 
The \f3jhat command parses a Java heap dump file and starts a web server. The \f3jhat command lets you to browse heap dumps with your favorite web browser. The \f3jhat command supports predesigned queries such as show all instances of a known class \f3MyClass, and Object Query Language (OQL). OQL is similar to SQL, except for querying heap dumps. Help on OQL is available from the OQL help page shown by the \f3jhat command. With the default port, OQL help is available at http://localhost:7000/oqlhelp/


There are several ways to generate a Java heap dump:

 0.2i 
Use the \f3jmap -dump option to obtain a heap dump at runtime. See jmap(1).

 0.2i 
Use the \f3jconsole option to obtain a heap dump through \f3HotSpotDiagnosticMXBean at runtime. See jconsole(1) and the \f3HotSpotDiagnosticMXBean interface description at http://docs.oracle.com/javase/8/docs/jre/api/management/extension/com/sun/management/HotSpotDiagnosticMXBean.html

 0.2i 
Heap dump is generated when an \f3OutOfMemoryError is thrown by specifying the \f3-XX:+HeapDumpOnOutOfMemoryError Java Virtual Machine (JVM) option.

 0.2i 
Use the \f3hprof command. See the HPROF: A Heap/CPU Profiling Tool at http://docs.oracle.com/javase/8/docs/technotes/samples/hprof.html

 OPTIONS 

-stack false|true


Turns off tracking object allocation call stack. If allocation site information is not available in the heap dump, then you have to set this flag to \f3false. The default is \f3true.


-refs false|true


Turns off tracking of references to objects. Default is \f3true. By default, back pointers, which are objects that point to a specified object such as referrers or incoming references, are calculated for all objects in the heap.


-port port-number


Sets the port for the \f3jhat HTTP server. Default is 7000.


-exclude exclude-file


Specifies a file that lists data members that should be excluded from the reachable objects query. For example, if the file lists \f3java.lang.String.value, then, then whenever the list of objects that are reachable from a specific object \f3o are calculated, reference paths that involve \f3java.lang.String.value field are not considered.


-baseline exclude-file


Specifies a baseline heap dump. Objects in both heap dumps with the same object ID are marked as not being new. Other objects are marked as new. This is useful for comparing two different heap dumps.


-debug int


Sets the debug level for this tool. A level of 0 means no debug output. Set higher values for more verbose modes.


-version


Reports the release number and exits


-h


Dsiplays a help message and exits.


-help


Displays a help message and exits.


-Jflag


Passes \f3flag to the Java Virtual Machine on which the \f3jhat command is running. For example, \f3-J-Xmx512m to use a maximum heap size of 512 MB.

 SEE ALSO 
 0.2i 
jmap(1)

 0.2i 
jconsole(1)

 0.2i 
HPROF: A Heap/CPU Profiling Tool at http://docs.oracle.com/javase/8/docs/technotes/samples/hprof.html




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