man > jhat(1)

jhat(1)                                 Troubleshooting Tools                                jhat(1)

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 #<number> to the file name,
              for example, myfile.hprof#3.

DESCRIPTION
       The jhat command parses a Java heap dump file and starts a web server. The jhat command  lets
       you  to  browse  heap  dumps  with  your  favorite  web  browser.  The  jhat command supports
       predesigned queries such as show all instances of a known class  MyClass,  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 jhat command. With the default port,  OQL  help
       is available at http://localhost:7000/oqlhelp/

       There are several ways to generate a Java heap dump:

       • Use the jmap -dump option to obtain a heap dump at runtime. See jmap(1).

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

       • Heap   dump   is   generated   when   an  OutOfMemoryError  is  thrown  by  specifying  the
         -XX:+HeapDumpOnOutOfMemoryError Java Virtual Machine (JVM) option.

       • Use   the   hprof   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 false. The default is
              true.

       -refs false|true
              Turns off tracking of references  to  objects.  Default  is  true.  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 jhat 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 java.lang.String.value, then, then
              whenever the list of  objects  that  are  reachable  from  a  specific  object  o  are
              calculated,   reference  paths  that  involve  java.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  flag  to  the  Java  Virtual Machine on which the jhat command is running. For
              example, -J-Xmx512m to use a maximum heap size of 512 MB.

SEE ALSO
       • jmap(1)

       • jconsole(1)

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

JDK 8                                     21 November 2013                                   jhat(1)