1jhat(1)                     General Commands Manual                    jhat(1)
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Name

6       jhat - Java Heap Analysis Tool
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SYNOPSIS

9       jhat [ options ] <heap-dump-file>
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PARAMETERS

14          options
15             Options,  if  used,  should  follow immediately after the command
16             name.
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18          heap-dump-file
19             Java binary heap dump file to be browsed. For a  dump  file  that
20             contains  multiple  heap dumps, you may specify which dump in the
21             file  by  appending   "#<number>   to   the   file   name,   i.e.
22             "foo.hprof#3".
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DESCRIPTION

26       The jhat command parses a java heap dump file and launches a webserver.
27       jhat enables you to browse heap dumps using your  favorite  webbrowser.
28       jhat  supports  pre-designed  queries (such as 'show all instances of a
29       known class "Foo"') as well as OQL (Object Query Language) - a SQL-like
30       query  language  to query heap dumps. Help on OQL is available from the
31       OQL help page shown by jhat. With the default port, OQL help is  avail‐
32       able at http://localhost:7000/oqlhelp/
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34       There are several ways to generate a java heap dump:
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36          o Use jmap(1) -dump option to obtain a heap dump at runtime;
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38          o Use jconsole(1) option to obtain a heap dump via HotSpotDiagnos‐
39            ticMXBean @
40            http://docs.oracle.com/javase/7/docs/jre/api/management/exten‐
41            sion/com/sun/management/HotSpotDiagnosticMXBean.html at runtime;
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43          o Heap dump will be generated when OutOfMemoryError is thrown by
44            specifying -XX:+HeapDumpOnOutOfMemoryError VM option;
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46          o Use hprof @
47            https://docs.oracle.com/javase/7/docs/technotes/sam‐
48            ples/hprof.html.
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51       NOTE: This tool is experimental and may not be available in future ver‐
52       sions of the JDK.
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OPTIONS

55          -stack false/true
56             Turn off tracking object allocation call stack. Note that if
57             allocation site information is not available in the heap dump,
58             you have to set this flag to false. Default is true.
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60          -refs false/true
61             Turn off tracking of references to objects. Default is true. By
62             default, back pointers (objects pointing to a given object a.k.a
63             referrers or in-coming references) are calculated for all objects
64             in the heap.
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66          -port port-number
67             Set the port for the jhat's HTTP server. Default is 7000.
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69          -exclude exclude-file
70             Specify a file that lists data members that should be excluded
71             from the "reachable objects" query. For example, if the file
72             lists java.lang.String.value, then, whenever list of objects
73             reachable from a specific object "o" are calculated, reference
74             paths involving java.lang.String.value field will not considered.
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76          -baseline baseline-dump-file
77             Specify a baseline heap dump. Objects in both heap dumps with the
78             same object ID will be marked as not being "new". Other objects
79             will be marked as "new". This is useful while comparing two dif‐
80             ferent heap dumps.
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82          -debug int
83             Set debug level for this tool. 0 means no debug output. Set
84             higher values for more verbose modes.
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86          -version
87             Report version number and exit.
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89          -h Output help message and exit.
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91          -help
92             Output help message and exit.
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94          -J<flag>
95             Pass <flag> to the Java virtual machine on which jhat is run. For
96             example, -J-Xmx512m to use a maximum heap size of 512MB.
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SEE ALSO

100          o jmap(1)
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102          o jconsole(1)
103
104          o hprof - Heap and CPU profiling tool @
105            https://docs.oracle.com/javase/7/docs/technotes/sam‐
106            ples/hprof.html.
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109                                  16 Mar 2012                          jhat(1)
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