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jhat(1)                                                                                              jhat(1)



NAME
       jhat - Java Heap Analysis Tool


SYNOPSIS
       jhat [ options ] <heap-dump-file>




PARAMETERS
       options
          Options, if used, should follow immediately after the command name.

       heap-dump-file
          Java  binary  heap dump file to be browsed. For a dump file that contains multiple heap dumps, you
          may specify which dump in the file by appending "#<number> to the file name, i.e. "foo.hprof#3".


DESCRIPTION
       The jhat command parses a java heap dump file and launches a webserver. jhat enables  you  to  browse
       heap  dumps  using  your  favorite  webbrowser. jhat supports pre-designed queries (such as 'show all
       instances of a known class "Foo"') as well as OQL (Object Query Language) - a SQL-like query language
       to  query heap dumps. Help on OQL is available from the OQL help page shown by jhat. With the default
       port, OQL help is available at http://localhost:7000/oqlhelp/


       There are several ways to generate a java heap dump:


          * Use jmap -dump option to obtain a heap dump at runtime;

          * Use jconsole option to obtain a heap dump via HotSpotDiagnosticMXBean @
            http://java.sun.com/javase/6/docs/jre/api/management/extension/com/sun/management/HotSpotDiag-
            nosticsMXBean.html at runtime;

          * Heap dump will be generated when OutOfMemoryError is thrown by specifying -XX:+HeapDumpOnOut-OfMemoryError -XX:+HeapDumpOnOutOfMemoryError
            OfMemoryError VM option;

          * Use hprof @
            http://java.sun.com/developer/technicalArticles/Programming/HPROF.html.



       NOTE: This tool is experimental and may not be available in future versions of the JDK.


OPTIONS
       -stack false/true
          Turn off tracking object allocation call stack. Note that if allocation site information is not
          available in the heap dump, you have to set this flag to false. Default is true.

       -refs false/true
          Turn off tracking of references to objects. Default is true. By default, back pointers (objects
          pointing to a given object a.k.a referrers or in-coming references) are calculated for all objects
          in the heap.

       -port port-number
          Set the port for the jhat's HTTP server. Default is 7000.

       -exclude exclude-file
          Specify a file that lists data members that should be excluded from the "reachable objects" query.
          For example, if the file lists java.lang.String.value, then, whenever list of objects reachable
          from a specific object "o" are calculated, reference paths involving java.lang.String.value field
          will not considered.

       -baseline baseline-dump-file
          Specify a baseline heap dump. Objects in both heap dumps with the same object ID will be marked as
          not being "new". Other objects will be marked as "new". This is useful while comparing two differ-ent different
          ent heap dumps.

       -debug int
          Set debug level for this tool. 0 means no debug output. Set higher values for more verbose modes.

       -version
          Report version number and exit.

       -h
          Output help message and exit.

       -help
          Output help message and exit.

       -J<flag>
          Pass <flag> to the Java virtual machine on which jhat is run. For example, -J-Xmx512m to use a
          maximum heap size of 512MB.


SEE ALSO
          * jmap - Java Memory Map

          * jconsole - Java Monitoring and Management Console

          * hprof - Heap and CPU profiling tool @
            http://java.sun.com/developer/technicalArticles/Programming/HPROF.html








                                                 05 Aug 2006                                         jhat(1)