jhat(1)                    OpenBSD Reference 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
       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/HotSpotDiagnosticsMXBean.html
            at runtime;

          * Heap dump will be generated when OutOfMemoryError is thrown by
            specifying -XX:+HeapDumpOnOutOfMemoryError 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 different
          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)
