'\" t+
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.\"  Copyright (c) 2006, 2013, Oracle and/or its affiliates. All rights reserved.+
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.\"+
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.\" DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.+
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.\"+
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.\" This code is free software; you can redistribute it and/or modify it+
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.\" under the terms of the GNU General Public License version 2 only, as+
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.\" published by the Free Software Foundation.+
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.\"+
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.\" This code is distributed in the hope that it will be useful, but WITHOUT+
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.\" ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or+
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.\" FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License+
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.\" version 2 for more details (a copy is included in the LICENSE file that+
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.\" accompanied this code).+
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.\"+
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.\" You should have received a copy of the GNU General Public License version+
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.\" 2 along with this work; if not, write to the Free Software Foundation,+
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.\" Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.+
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.\"+
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.\" Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA+
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.\" or visit www.oracle.com if you need additional information or have any+
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.\" questions.+
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.\"+
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.\"     Arch: generic+
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.\"     Software: JDK 8+
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.\"     Date: 21 November 2013+
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.\"     SectDesc: Troubleshooting Tools+
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.\"     Title: jhat.1+
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.\"+
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.if n .pl 99999+
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.TH jhat 1 "21 November 2013" "JDK 8" "Troubleshooting Tools"+
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.\" -----------------------------------------------------------------+
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.\" * Define some portability stuff+
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.\" -----------------------------------------------------------------+
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.\" ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~+
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.\" http://bugs.debian.org/507673+
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.\" http://lists.gnu.org/archive/html/groff/2009-02/msg00013.html+
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.\" ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~+
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.ie \n(.g .ds Aq \(aq+
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.el       .ds Aq '+
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.\" -----------------------------------------------------------------+
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.\" * set default formatting+
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.\" -----------------------------------------------------------------+
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.\" disable hyphenation+
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.nh+
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.\" disable justification (adjust text to left margin only)+
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.ad l+
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.\" -----------------------------------------------------------------+
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.\" * MAIN CONTENT STARTS HERE *+
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.\" -----------------------------------------------------------------+
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+
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.SH NAME    +
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jhat \- Analyzes the Java heap\&. This command is experimental and unsupported\&.+
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.SH SYNOPSIS    +
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.sp     +
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.nf     +
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+
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\fBjhat\fR [ \fIoptions\fR ] \fIheap\-dump\-file\fR +
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.fi     +
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.sp     +
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.TP     +
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\fIoptions\fR+
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The command-line options\&. See Options\&.+
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.TP     +
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\fIheap-dump-file\fR+
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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\&.+
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.SH DESCRIPTION    +
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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/+
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.PP+
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There are several ways to generate a Java heap dump:+
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.TP 0.2i    +
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\(bu+
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Use the \f3jmap -dump\fR option to obtain a heap dump at runtime\&. See jmap(1)\&.+
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.TP 0.2i    +
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\(bu+
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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+
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.TP 0.2i    +
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\(bu+
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Heap dump is generated when an \f3OutOfMemoryError\fR is thrown by specifying the \f3-XX:+HeapDumpOnOutOfMemoryError\fR Java Virtual Machine (JVM) option\&.+
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.TP 0.2i    +
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\(bu+
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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+
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.SH OPTIONS    +
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.TP+
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-stack false|true+
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.br+
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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\&.+
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.TP+
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-refs false|true+
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.br+
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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\&.+
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.TP+
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-port \fIport-number\fR+
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.br+
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Sets the port for the \f3jhat\fR HTTP server\&. Default is 7000\&.+
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.TP+
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-exclude \fIexclude-file\fR+
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.br+
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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\&.+
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.TP+
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-baseline \fIexclude-file\fR+
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.br+
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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\&.+
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.TP+
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-debug \fIint\fR+
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.br+
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Sets the debug level for this tool\&. A level of 0 means no debug output\&. Set higher values for more verbose modes\&.+
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.TP+
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-version+
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.br+
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Reports the release number and exits+
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.TP+
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-h+
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.br+
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Dsiplays a help message and exits\&.+
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.TP+
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-help+
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.br+
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Displays a help message and exits\&.+
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.TP+
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-J\fIflag\fR+
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.br+
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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\&.+
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.SH SEE\ ALSO    +
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.TP 0.2i    +
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\(bu+
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jmap(1)+
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.TP 0.2i    +
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\(bu+
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jconsole(1)+
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.TP 0.2i    +
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\(bu+
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HPROF: A Heap/CPU Profiling Tool at http://docs\&.oracle\&.com/javase/8/docs/technotes/samples/hprof\&.html+
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.RE+
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.br+
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'pl 8.5i+
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'bp+
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