1jhat(1)                      Troubleshooting Tools                     jhat(1)
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NAME

6       jhat - Analyzes the Java heap. This command is experimental and
7       unsupported.
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SYNOPSIS

10       jhat [ options ] heap-dump-file
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12
13       options
14              The command-line options. See Options.
15
16       heap-dump-file
17              Java binary heap dump file to be browsed. For a dump file that
18              contains multiple heap dumps, you can specify which dump in the
19              file by appending #<number> to the file name, for example,
20              myfile.hprof#3.
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DESCRIPTION

23       The jhat command parses a Java heap dump file and starts a web server.
24       The jhat command lets you to browse heap dumps with your favorite web
25       browser. The jhat command supports predesigned queries such as show all
26       instances of a known class MyClass, and Object Query Language (OQL).
27       OQL is similar to SQL, except for querying heap dumps. Help on OQL is
28       available from the OQL help page shown by the jhat command. With the
29       default port, OQL help is available at http://localhost:7000/oqlhelp/
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31       There are several ways to generate a Java heap dump:
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33       · Use the jmap -dump option to obtain a heap dump at runtime. See
34         jmap(1).
35
36       · Use the jconsole option to obtain a heap dump through
37         HotSpotDiagnosticMXBean at runtime. See jconsole(1) and the
38         HotSpotDiagnosticMXBean interface description at
39         http://docs.oracle.com/javase/8/docs/jre/api/management/extension/com/sun/management/HotSpotDiagnosticMXBean.html
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41       · Heap dump is generated when an OutOfMemoryError is thrown by
42         specifying the -XX:+HeapDumpOnOutOfMemoryError Java Virtual Machine
43         (JVM) option.
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45       · Use the hprof command. See the HPROF: A Heap/CPU Profiling Tool at
46         http://docs.oracle.com/javase/8/docs/technotes/samples/hprof.html
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OPTIONS

49       -stack false|true
50              Turns off tracking object allocation call stack. If allocation
51              site information is not available in the heap dump, then you
52              have to set this flag to false. The default is true.
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54       -refs false|true
55              Turns off tracking of references to objects. Default is true. By
56              default, back pointers, which are objects that point to a
57              specified object such as referrers or incoming references, are
58              calculated for all objects in the heap.
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60       -port port-number
61              Sets the port for the jhat HTTP server. Default is 7000.
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63       -exclude exclude-file
64              Specifies a file that lists data members that should be excluded
65              from the reachable objects query. For example, if the file lists
66              java.lang.String.value, then, then whenever the list of objects
67              that are reachable from a specific object o are calculated,
68              reference paths that involve java.lang.String.value field are
69              not considered.
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71       -baseline exclude-file
72              Specifies a baseline heap dump. Objects in both heap dumps with
73              the same object ID are marked as not being new. Other objects
74              are marked as new. This is useful for comparing two different
75              heap dumps.
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77       -debug int
78              Sets the debug level for this tool. A level of 0 means no debug
79              output. Set higher values for more verbose modes.
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81       -version
82              Reports the release number and exits
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84       -h
85              Dsiplays a help message and exits.
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87       -help
88              Displays a help message and exits.
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90       -Jflag
91              Passes flag to the Java Virtual Machine on which the jhat
92              command is running. For example, -J-Xmx512m to use a maximum
93              heap size of 512 MB.
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SEE ALSO

96       · jmap(1)
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98       · jconsole(1)
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100       · HPROF: A Heap/CPU Profiling Tool at
101         http://docs.oracle.com/javase/8/docs/technotes/samples/hprof.html
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105JDK 8                          21 November 2013                        jhat(1)
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