jhat(1)                     General Commands Manual                    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  avail-
       able at http://localhost:7000/oqlhelp/

       There are several ways to generate a java heap dump:

          o Use jmap(1) -dump option to obtain a heap dump at runtime;

          o Use jconsole(1) option to obtain a heap dump via HotSpotDiagnos-
            ticMXBean @
            http://docs.oracle.com/javase/7/docs/jre/api/management/exten-
            sion/com/sun/management/HotSpotDiagnosticMXBean.html at runtime;

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

          o Use hprof.


       NOTE: This tool is experimental and may not be available in future ver-
       sions 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 dif-
             ferent 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
          o jmap(1)

          o jconsole(1)

          o hprof - Heap and CPU profiling tool


                                  18 Jul 2013                          jhat(1)
