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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
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| 'pl 8.5i
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| 'bp
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