jhat(1)jhat(1)NAME
jhat - Java Heap Analysis Tool
SYNOPSIS
jhat [ options ] <heap-dump-file>
PARAMETERS
options
Options, if used, should follow immediately after the command name.
heap-dump-file
Java binary heap dump file to be browsed. For a dump file that con‐
tains multiple heap dumps, you may specify which dump in the file by
appending "#<number> to the file name, i.e. "foo.hprof#3".
DESCRIPTION
The jhat command parses a java heap dump file and launches a webserver.
jhat enables you to browse heap dumps using your favorite webbrowser.
jhat supports pre-designed queries (such as 'show all instances of a
known class "Foo"') as well as OQL (Object Query Language) - a SQL-like
query language to query heap dumps. Help on OQL is available from the
OQL help page shown by jhat. With the default port, OQL help is avail‐
able at http://localhost:7000/oqlhelp/
There are several ways to generate a java heap dump:
* Use jmap -dump option to obtain a heap dump at runtime;
* Use jconsole option to obtain a heap dump via HotSpotDiagnos‐
ticMXBean @
http://java.sun.com/javase/6/docs/jre/api/management/exten‐
sion/com/sun/management/HotSpotDiagnosticsMXBean.html at runtime;
* Heap dump will be generated when OutOfMemoryError is thrown by
specifying -XX:+HeapDumpOnOutOfMemoryError VM option;
* Use hprof @
http://java.sun.com/developer/technicalArticles/Program‐
ming/HPROF.html.
NOTE: This tool is experimental and may not be available in future ver‐
sions of the JDK.
OPTIONS-stack false/true
Turn off tracking object allocation call stack. Note that if alloca‐
tion site information is not available in the heap dump, you have to
set this flag to false. Default is true.
-refs false/true
Turn off tracking of references to objects. Default is true. By
default, back pointers (objects pointing to a given object a.k.a
referrers or in-coming references) are calculated for all objects in
the heap.
-port port-number
Set the port for the jhat's HTTP server. Default is 7000.
-exclude exclude-file
Specify 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, whenever list of objects reachable
from a specific object "o" are calculated, reference paths involving
java.lang.String.value field will not considered.
-baseline baseline-dump-file
Specify a baseline heap dump. Objects in both heap dumps with the
same object ID will be marked as not being "new". Other objects will
be marked as "new". This is useful while comparing two different
heap dumps.
-debug int
Set debug level for this tool. 0 means no debug output. Set higher
values for more verbose modes.
-version
Report version number and exit.
-h
Output help message and exit.
-help
Output help message and exit.
-J<flag>
Pass <flag> to the Java virtual machine on which jhat is run. For
example, -J-Xmx512m to use a maximum heap size of 512MB.
SEE ALSO
* jmap - Java Memory Map
* jconsole - Java Monitoring and Management Console
* hprof - Heap and CPU profiling tool @
http://java.sun.com/developer/technicalArticles/Program‐
ming/HPROF.html
05 Aug 2006 jhat(1)
