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.\"     Arch: generic

.\"     Software: JDK 8

.\"     Date: 21 November 2013

.\"     SectDesc: Troubleshooting Tools

.\"     Title: jhat.1

.\"

.if n .pl 99999

.TH jhat 1 "21 November 2013" "JDK 8" "Troubleshooting Tools"

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.SH NAME    

jhat \- Analyzes the Java heap\&. This command is experimental and unsupported\&.

.SH SYNOPSIS    

.sp     

.nf     

\fBjhat\fR [ \fIoptions\fR ] \fIheap\-dump\-file\fR 

.fi     

.sp     

.TP     

\fIoptions\fR

The command-line options\&. See Options\&.

.TP     

\fIheap-dump-file\fR

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 \f3#<number>\fR to the file name, for example, \f3myfile\&.hprof#3\fR\&.

.SH DESCRIPTION    

The \f3jhat\fR command parses a Java heap dump file and starts a web server\&. The \f3jhat\fR command lets you to browse heap dumps with your favorite web browser\&. The \f3jhat\fR command supports predesigned queries such as show all instances of a known class \f3MyClass\fR, 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 \f3jhat\fR command\&. With the default port, OQL help is available at http://localhost:7000/oqlhelp/

.PP

There are several ways to generate a Java heap dump:

.TP 0.2i    

\(bu

Use the \f3jmap -dump\fR option to obtain a heap dump at runtime\&. See jmap(1)\&.

.TP 0.2i    

\(bu

Use the \f3jconsole\fR option to obtain a heap dump through \f3HotSpotDiagnosticMXBean\fR at runtime\&. See jconsole(1) and the \f3HotSpotDiagnosticMXBean\fR interface description at http://docs\&.oracle\&.com/javase/8/docs/jre/api/management/extension/com/sun/management/HotSpotDiagnosticMXBean\&.html

.TP 0.2i    

\(bu

Heap dump is generated when an \f3OutOfMemoryError\fR is thrown by specifying the \f3-XX:+HeapDumpOnOutOfMemoryError\fR Java Virtual Machine (JVM) option\&.

.TP 0.2i    

\(bu

Use the \f3hprof\fR command\&. See the HPROF: A Heap/CPU Profiling Tool at http://docs\&.oracle\&.com/javase/8/docs/technotes/samples/hprof\&.html

.SH OPTIONS    

.TP

-stack false|true

.br

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 \f3false\fR\&. The default is \f3true\fR\&.

.TP

-refs false|true

.br

Turns off tracking of references to objects\&. Default is \f3true\fR\&. 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\&.

.TP

-port \fIport-number\fR

.br

Sets the port for the \f3jhat\fR HTTP server\&. Default is 7000\&.

.TP

-exclude \fIexclude-file\fR

.br

Specifies a file that lists data members that should be excluded from the reachable objects query\&. For example, if the file lists \f3java\&.lang\&.String\&.value\fR, then, then whenever the list of objects that are reachable from a specific object \f3o\fR are calculated, reference paths that involve \f3java\&.lang\&.String\&.value\fR field are not considered\&.

.TP

-baseline \fIexclude-file\fR

.br

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\&.

.TP

-debug \fIint\fR

.br

Sets the debug level for this tool\&. A level of 0 means no debug output\&. Set higher values for more verbose modes\&.

.TP

-version

.br

Reports the release number and exits

.TP

-h

.br

Dsiplays a help message and exits\&.

.TP

-help

.br

Displays a help message and exits\&.

.TP

-J\fIflag\fR

.br

Passes \f3flag\fR to the Java Virtual Machine on which the \f3jhat\fR command is running\&. For example, \f3-J-Xmx512m\fR to use a maximum heap size of 512 MB\&.

.SH SEE\ ALSO    

.TP 0.2i    

\(bu

jmap(1)

.TP 0.2i    

\(bu

jconsole(1)

.TP 0.2i    

\(bu

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

.RE

.br

'pl 8.5i

'bp