jhat Man page

jhat Troubleshooting Tools jhat

NAME

jhat – Analyzes the Java heap. This command is experimental and
unsupported.

SYNOPSIS

jhat [ options ] heap-dump-file

options
The command-line options. See Options.

heap-dump-file
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 # to the file name, for example,
myfile.hprof#3.

DESCRIPTION

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

There are several ways to generate a Java heap dump:

· Use the jmap -dump option to obtain a heap dump at runtime. See
jmap.

· Use the jconsole option to obtain a heap dump through
HotSpotDiagnosticMXBean at runtime. See jconsole and the
HotSpotDiagnosticMXBean interface description at
http://docs.oracle.com/javase/8/docs/jre/api/management/extension/com/sun/management/HotSpotDiagnosticMXBean.html

· Heap dump is generated when an OutOfMemoryError is thrown by
specifying the -XX:+HeapDumpOnOutOfMemoryError Java Virtual Machine
(JVM) option.

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

OPTIONS

-stack false|true
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 false. The default is true.

-refs false|true
Turns off tracking of references to objects. Default is true. 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.

-port port-number
Sets the port for the jhat HTTP server. Default is 7000.

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

-baseline exclude-file
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.

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

-version
Reports the release number and exits

-h
Dsiplays a help message and exits.

-help
Displays a help message and exits.

-Jflag
Passes flag to the Java Virtual Machine on which the jhat
command is running. For example, -J-Xmx512m to use a maximum
heap size of 512 MB.

SEE ALSO

· jmap

· jconsole

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

JDK 8 21 November 2013 jhat