jhat(1) - phpMan

jhat(1) Troubleshooting Tools jhat(1)

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 #<number> 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:

o Use the jmap -dump option to obtain a heap dump at runtime. See jmap(1).

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

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

o 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.