Hi,
Jay SenSharma

Jay SenSharma

Many times we want to Generate the Heap Dump to see what all objects are created inside the JVMs Heap space. The Heap Dump tells us that what all objects are created inside the JVM and what is the size of those Objects. Based on this analysis we can findout that what all objects (Application Objects/Platform Objects) are consuming more memory inside the heap.

Here is a Basic Step to enable the Jhat tool to generate the Heap Dump of our WebLogic Server and a brief intro of using this Great and wonderful tool.
Jhat tool comes free and available inside the “<JAVA_HOME>bin” directory (from JDK1.6 onwards only). If you are using Jdk 1.5 or Lower version then u need to separately download the Jhat tool.from “https://hat.dev.java.net/
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Step1). Open the “startWebLogic.sh”(Unix Based OS) or “startWebLogic.cmd”(Windows OS)  and then add the JAVA_OPTIONS inside it as following:
@REM **********WINDOWS Operating Systems<(startWebLogic.cmd)******************
@REM
@REM Call setDomainEnv here.
set DOMAIN_HOME=C:bea103user_projectsdomainsWS_Security_Domain
for %%i in ("%DOMAIN_HOME%") do set DOMAIN_HOME=%%~fsi
call "%DOMAIN_HOME%binsetDomainEnv.cmd" %*
set SAVE_JAVA_OPTIONS=%JAVA_OPTIONS% -Xrunhprof:format=b,file=MyHeapDump.hprof
set SAVE_CLASSPATH=%CLASSPATH%
#************Unix Based Operating Systems<(startWebLogic.sh)***********
#
# Call setDomainEnv here.
DOMAIN_HOME="C:/bea103/user_projects/domains/WLST_Domain"
. ${DOMAIN_HOME}/bin/setDomainEnv.sh $*
SAVE_JAVA_OPTIONS="${JAVA_OPTIONS}"   -Xrunhprof:format=b,file=MyHeapDump.hprof
SAVE_CLASSPATH="${CLASSPATH}"
Step2). Now restart Your Server. As soon as you will start your Server you will find that “MyHeapDump.hprof” file is created inside your <DOMAIN_HOME> root directory:
Heap Dump Location

Heap Dump Location

Wait For Some time 4-5 Minutes to get the complete heap Dump

Step3). Open the HeapDump using the Jhat tool like following:
C:bea103jdk160_05bin>jhat -J-mx1024m  C:bea103user_projectsdomainsWS_Security_DomainMyHeapDump.hprof

OR place the file in some other location before opening it…
C:bea103jdk160_05bin>jhat      -J-mx1024m       C:myHeapDumpsMyHeapDump.hprof
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Step4). As soon as u run the Obove command jhat tool starts a Http Server on default port 7000…Please open a browser with the following URL:
http://localhost:7000
Opening Jhat Console

Opening Jhat Console

jhat Histogram Analysis

jhat Histogram Analysis

Jhat Object Query Language Editor

Jhat Object Query Language Editor

Jhat Non Product Instance Counter

Jhat Non Product Instance Counter

Jhat Platform/Non-Platform Instance Counter

Jhat Platform/Non-Platform Instance Counter

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***** **** *** **____Advanced Jhat Analysis____ ***** **** *** **
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Step5). Object Query Language (OQL)
OQL is SQL-like query language to query Java heap. OQL allows to filter/select information wanted from Java heap. While pre-defined queries such as “show all instances of class X” are already supported by HAT, OQL adds more flexibility. OQL is based on JavaScript expression language.
OQL query is of the form
select <JavaScript expression to select>
[ from [instanceof] <class name> <identifier>
[ where <JavaScript boolean expression to filter> ] ]
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(OQL) Object Query Language Querie

(OQL) Object Query Language Querie

(OQL) Object Query Language Querries

(OQL) Object Query Language Querries

(OQL) Object Query Language Querries

(OQL) Object Query Language Querries

(OQL) Object Query Language Querries

(OQL) Object Query Language Querries

(OQL) Object Query Language Querries

(OQL) Object Query Language Querries

(OQL) Object Query Language Querries

(OQL) Object Query Language Querries

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Issues U May Face While Using Jhat for Analysis:

Issue-1). While reading Heap Dump using Jhat u may find following error:
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Reading from C:bea103user_projectsdomainsTest_DomainMyHeapDump.hprof…
Dump file created Sun Jul 11 20:22:53 IST 2010
java.io.IOException: Unrecognized heap dump sub-record type:  0
at com.sun.tools.hat.internal.parser.HprofReader.readHeapDump(HprofReader.java:489)
at com.sun.tools.hat.internal.parser.HprofReader.read(HprofReader.java:226)
at com.sun.tools.hat.internal.parser.Reader.readFile(Reader.java:79)
at com.sun.tools.hat.Main.main(Main.java:143)
Solution: Most of the time this means that the VM did not write the heap dump properly. At some point in the file, everything is zeroed out, hence the unknown sub-record type 0. There is not much you can do but get another heap dump. Or try to download “Eclipse Memory Analyzer(http://www.eclipse.org/proposals/memory-analyzer/) and just say file—>open—>MyHeapDump.hprof “
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Issue-2). While Killing your Server Profiler will try to generate the HeapDump (around 30 MB minimum size with WLS Server) you may get the following error in the WLS Server stdout:
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HPROF ERROR: Missing jclass when fields needed [hprof_class.c:647]
HPROF ERROR: Trouble with unprepared classes [hprof_reference.c:384]
HPROF ERROR: Missing jclass when fields needed [hprof_class.c:647]
HPROF ERROR: Trouble with unprepared classes [hprof_reference.c:384]
allocation sites … done.
<Jul 11, 2010 8:11:06 PM IST> <Error> <> <BEA-000000> <THREAD DUMP from JVM taken at ‘Sun Jul 11 20:07:47 2010’>
Solution: Please collect another Heap Dump or use “Eclipse Memory Analyzer”

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WORKAROUND

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Use the “Jmap” utility (Which comes with JDK1.6 default or download it separately) to generate the Binary Heap Dump File and then read it using Jhat tool….    http://middlewaremagic.com/weblogic/?p=2241
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Why “Jmap”?
Jmap is much better than Jhat utility because to start with Jmap utility u need not to apply any JAVA_OPTION on the WebLogic Server … you can directly start with any WebLogic Server which is  Running on Sun JDK …. All u need to do is …Just find the Process ID of that WLS Server…thats all.
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Step1). Find the process ID of your Server.
Step2). Run the following command: (Suppose 5552 is the Process ID of your Server Process)
C:bea103jdk160_05bin>jmap -dump:format=b,file=heapJMap.bin 5552
Dumping heap to C:bea103jdk160_05binheapJMap.bin …
Heap dump file created
Step3). Make sure that while reading the Binary Heap Dump using JHat …u set the Heap Size to 1024 or according to the Heap dump size….
C:bea103jdk160_05bin>jhat -J-Xmx1024m heapJMap.bin
Reading from heapJMap.bin…
Dump file created Mon Jul 12 10:05:58 IST 2010
Snapshot read, resolving…
Chasing references, expect 239 dots………….
…………………………………………
Eliminating duplicate references…………….
…………………………………………
Snapshot resolved.
Started HTTP server on port 7000
Server is ready.
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Thanks
Jay SenSharma
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