Updating Weblogic License

Updating License file when it expires or moved from one version to another version of weblogic server and Installation of Patches Plugins :
[1] Install and configure WebLogic Server service packs (old versions) and patches

http://download.oracle.com/docs/cd/E14759_01/index.htm

[2] Install Web Server plug-ins if required on supported platforms

http://download.oracle.com/docs/cd/E13196_01/platform/suppconfigs/configs81/81_over/add-ons.html

[3] Updating WebLogic License file

#This below info is written by pavan
WebLogic License Updating
Here we go to update the BEA License file ...

What happens if it is not updated?

1. We cannot have more instances on the same domain it is limiting to 5 instances only.

2. If you had the 5th instance including your Admin in RUNNING state but, you cannot access the console.

What is the resolution for this situation?

Update your BEA/Oracle Licence as per the given steps.

Stop all server instances which are already running.

Update this on every machine.

Remove "servers" folder

1. Click the license link:http://licensecodes.oracle.com/bea.html

choose here "BEA WebLogic Server Products" As per your operating environment you can choose the update.zip file.

2. Download you application suitable license zip file I have choosen version as "9.2 - 9.2mp3" -- LIC-WLSP92

3. Take a backup of the old license file

cp license.bea license.bea_bkp

4. Place the downloaded new license file (license.bea_new) in the BEA_HOME

4. Run the following command.

$ ./UpdateLicense.sh license.bea_new

Here it will apply the new lincense modifications on to the license.bea file directly.

If this command failed revert back to the old backup.


Now your license is ready to use more than 5 users (Clustered environment).

Start the servers and check for availability of new license.

Weblogic UnInstallation in Solaris

Continuation of Weblogic Server Installation under Solaris 5.10 box
Weblogic Server Uninstallation in 3 Modes:
1.GUI
2.Console
3.Silent

2.Console Mode uninstallation of Weblogic Server in Solaris Box

1. Go to the following directory:
WL_HOME/uninstall
Here WL_HOME represents the directory in which you installed
WebLogic Server.
2. At the prompt, enter the following command:

 
bash-3.00$ cd bea
bash-3.00$ ls -l
total 40
-rwxr-xr-x   1 wluser   beaproject     851 Dec 17 10:51 UpdateLicense.sh
-rw-r--r--   1 wluser   beaproject      23 Dec 17 10:51 beahomelist
drwxr-xr-x   6 wluser   beaproject     512 Dec 17 10:51 jdk150_10
-rw-r--r--   1 wluser   beaproject   12081 Dec 17 10:51 license.bea
drwxr-xr-x   2 wluser   beaproject     512 Dec 17 10:52 logs
drwxr-xr-x   3 wluser   beaproject    1024 Dec 17 10:51 modules
-rw-r--r--   1 wluser   beaproject     917 Dec 17 10:52 registry.xml
drwxr-xr-x   3 wluser   beaproject     512 Dec 17 10:51 utils
drwxr-xr-x  10 wluser   beaproject     512 Dec 17 10:54 weblogic92
bash-3.00$ uninstall.sh -mode=console 

<----------------------- BEA Uninstaller - BEA Products ---------------------->

Welcome:


Welcome to the BEA Products uninstaller. If you wish to 
proceed with the uninstallation type Next, otherwise, please type 
Exit to cancel.

Enter [Exit][Next]>  

<----------------------- BEA Uninstaller - BEA Products ---------------------->

Choose Components to uninstall: 

-------------------------------

Check the BEA Products components you want to uninstall. 

    Release 9.2.2.0 

    |_____WebLogic Server [1] x
         |_____Server [1.1] x



Enter number exactly as it appears in brackets to toggle selection OR 

[Exit][Previous][Next]> 

 

<----------------------- BEA Uninstaller - BEA Products ---------------------->

Setting Up

 

<----------------------- BEA Uninstaller - BEA Products ---------------------->

Removing Files

<----------------------- BEA Uninstaller - BEA Products ---------------------->

Removing BEA Registry Entries

<----------------------- BEA Uninstaller - BEA Products ---------------------->

Uninstall Completed Successfully!

<----------------------- BEA Uninstaller - BEA Products ---------------------->

Uninstallation Complete

Uninstallation of selected components has completed successfully.

Press [Enter] to continue

bash-3.00$ cd bea 

bash-3.00$ ls -la
total 42
drwxr-xr-x   6 wluser   beaproject     512 Dec 18 06:41 .
drwxr-xr-x   6 wluser   beaproject     512 Dec 17 10:50 ..
-rwxr-xr-x   1 wluser   beaproject     851 Dec 17 10:51 UpdateLicense.sh
-rw-r--r--   1 wluser   beaproject      23 Dec 17 10:51 beahomelist
drwxr-xr-x   6 wluser   beaproject     512 Dec 17 10:51 jdk150_10
-rw-r--r--   1 wluser   beaproject   12081 Dec 17 10:51 license.bea
drwxr-xr-x   2 wluser   beaproject     512 Dec 17 10:52 logs
drwxr-xr-x   3 wluser   beaproject    1024 Dec 17 10:51 modules
-rw-r--r--   1 wluser   beaproject     324 Dec 18 06:40 registry.xml
drwxr-xr-x   3 wluser   beaproject     512 Dec 17 10:51 utils

Note: Weblogic92 folder disappear.


3.Uninstalling the Weblogic Server in Silent Mode

Go to the following directory: WL_HOME/uninstall Here WL_HOME represents the directory in which you installed WebLogic Server.
At the prompt, enter the following command:
bash-3.00$ sh uninstall.sh -mode=silent -log=/export/home/wluser/logs/uninstall.log

Weblogic Installation on Sun Solaris

When I was preparing for the WebLogic Certification there is a dedicated topic for Installing WebLogic. If you wish to prepare for the same, Let me share you my experiance with the Installation on Sun Solaris SPARC machine. You, smart WLA need to choose what kind of installation required for the environment first. Normally for the Developer who want to test their application frequently they don't need a Production installation,  At a given point of time you will get one or two hits to the application so the Development mode is sufficient. The Performance Engineer, work for pre-production environment tests requires Production installation. In the production environment the user hits to the application could be thousands at a any given time. So the need is huge you need Production mode installation. I hope, you should understand the basic differences between Development and Production mode installation perfectly then go ahead for the next section for experimenting. Here my focus on console type of installation which is most of the non-GUI environments requires and most of the WebLogic Administrator work from remote locations so this method is suggestable way. Other option GUI you can choose X11 forwarding with X emulator softwares.

Product Installation
[1] Install the JDK/JRE if required on supported platforms (if it is not included with jar distribution)
[2] Installing WebLogic Server on supported platforms

Installation Modes:
1. GUI
2. console
3. silent

Installing on Sun Solaris 5.10

When you are on the oracle download page you need to choose proper installer that should match your platform. If your system uses Sun Solaris 5.10, your installer could have a
server923_solaris32.bin(WebLogic 9.2 MP3) or wls1033_solaris32.bin (WebLogic 10.3.3/11g) as binary file name. If your installer has the .bin extension,that means the installer includes Java Development Kit (JDK).

To run the installer you need to use .bin file if you have it available on a CD or on Disk then , follow
these steps:
1.Logon to the system as the user whoever have previllages to work as WebLogic System Administrator.
2.Open a command-line shell.
3.Insert the WebLogic CD in the CD-ROM drive or disk where the bin file is located.

Change to the weblogic_platform directory on the CD or disk.
and Invoke the following command:

./server923_solaris32.bin -mode=console -Djava.io.tmpdir=/tmp -log=/export/home/wluser/logs/BEA_install.log

Note: Don't Copy the commands directly from pdf/webpage files to Unix/sunsolaris
console this may cause problem (Symbols can not be identified)

Sample installation Run given for your reference:

bash-3.00$ ls -lrt
-rwxr-xr-x 1 wluser beaproj 608240443 Dec 16 10:53 server922_solaris32.binbash-3.00$ ./server922_solaris32.bin mode=console
Invalid command line argument: [mode]. //Refer Note
#ERROR due to - missed before mode 2.Console Mode Installation
bash-3.00$ ./server922_solaris32.bin -mode=console
Extracting
0%....................................................................................................100% <----------------------------------------------- BEA Installer - BEA Products ---------------------------------------------->
Welcome:
--------
This installer will guide you through the installation of BEA Products. Type
"Next" or enter to proceed to the next prompt.
If you want to change data entered previously, type "Previous". You may quit the
installer at any time by typing "Exit".

Enter [Exit][Next]>


<----------------------------------------------- BEA Installer - BEA Products ---------------------------------------------->
BEA Systems License Agreement:
------------------------------
BEA SYSTEMS, INC. SOFTWARE LICENSE AGREEMENT
USE OF SOFTWARE ORDERED FROM BEA SYSTEMS, INC. ("BEA") IS PROVIDED ONLY UNDER
LICENSE FROM BEA. PLEASE READ THE FOLLOWING
LICENSE CAREFULLY AND INDICATE YOUR ACCEPTANCE BY CLICKING THE ACCEPTANCE BOX.
CERTAIN CAPITALIZED TERMS ARE DEFINED IN
SECTION 11.

1. LICENSE TERMS
a. WebLogic SDK Use. The terms of this Section 1(a) are applicable to you if
you have registered as a WebLogic SDK
customer. Subject to the terms of this Agreement, BEA grants to you a
non-exclusive, non-transferable, royalty-free license
to use WebLogic SDK solely for Development Use and Scale-Limited Personal Use for
the number of users and/or developers and
the number of CPU's, Servers and/or at the Sites, as specified at the time of
registration. Third party software products or
modules supplied by BEA, if any, may be used solely with the Software. All rights
not specifically granted to you herein are
retained by BEA.
b. WebLogic SDK Pro Use. The terms of this Section 1(b) are applicable to you if
you have registered as a WebLogic SDK Pro
customer. Subject to the terms of this Agreement, BEA grants to you a
non-exclusive, non-transferable, fee-bearing license to use WebLogic SDK Pro
solely for Development Use and Scale-Limited Commercial Use for the number of
users and/or developers
and the number of CPU's, Servers and/or at the Sites, as specified on BEA's
invoice. Third party software products or modules supplied by BEA, if any, may be
used solely with the Software. All rights not specifically granted to you herein
are retained by BEA.
c. Evaluation Use. The terms of this Section 1(c) are applicable to you if you
have registered as an Evaluation Use
customer. Subject to the terms of this Agreement, BEA grants to you a
non-exclusive, non-transferable, license to use the
Use above value or select another option:
1 - Yes, I agree with the terms of the license
2 - No, I do not agree with the terms of the license

Enter option number to select OR [Down][Exit][Previous]> 1


<----------------------------------------------- BEA Installer - BEA Products ---------------------------------------------->
Choose BEA Home Directory:
--------------------------
"BEA Home" = [Enter new value or use default "/export/home/wluser/bea"]

Enter new BEA Home OR [Exit][Previous][Next]>


<----------------------------------------------- BEA Installer - BEA Products ---------------------------------------------->
Choose Install Type:
--------------------
Select the type of installation you wish to perform.
->1Complete
Install the following software components and examples:
- WebLogic Server
- Workshop for WebLogic Platform
2Custom
Choose software components to install and perform optional configuration.


Enter index number to select OR [Exit][Previous][Next]> 2


<----------------------------------------------- BEA Installer - BEA Products ---------------------------------------------->
Choose Components to install:
-----------------------------
Release 9.2.2.0
_____WebLogic Server [1] x
_____Server [1.1] x
_____Server Examples [1.2] x
_____Web Server Plug-Ins [1.3]
_____Workshop for WebLogic Platform [2] x
_____Workshop [2.1] x
_____Workshop Examples [2.2] x

Enter number exactly as it appears in brackets to toggle selection OR
[Exit][Previous][Next]> 2


<----------------------------------------------- BEA Installer - BEA Products ---------------------------------------------->
Choose Components to install:
-----------------------------
Release 9.2.2.0
_____WebLogic Server [1] x
_____Server [1.1] x
_____Server Examples [1.2] x
_____Web Server Plug-Ins [1.3]
_____Workshop for WebLogic Platform [2]
_____Workshop [2.1]
_____Workshop Examples [2.2]

Enter number exactly as it appears in brackets to toggle selection OR
[Exit][Previous][Next]>


<----------------------------------------------- BEA Installer - BEA Products ---------------------------------------------->
Choose Product Installation Directories:
----------------------------------------
BEA Home Directory: [/export/home/wluser/bea]
Product Installation Directories:
"Default Product Home" = [Enter new value or use default
"/export/home/wluser/bea/weblogic92"]

Enter new Default Product Home OR [Exit][Previous][Next]>
Dec 16, 2008 11:04:46 AM java.util.prefs.FileSystemPreferences$2 run
INFO: Created user preferences directory.


<----------------------------------------------- BEA Installer - BEA Products ---------------------------------------------->
Installing files..
0% 25% 50% 75% 100%
[------------------------------------------------]
[***************************************************]

<----------------------------------------------- BEA Installer - BEA Products ---------------------------------------------->
Installing JDK....
0% 25% 50% 75% 100%
[------------------------------------------------]
[***************************************************]
Performing String Substitutions...

Creating Domains...


<----------------------------------------------- BEA Installer - BEA Products ---------------------------------------------->
Installation Complete
Congratulations! BEA Products has been successfully installed to
/export/home/wluser/bea/weblogic92.
Press [Enter] to continue or type [Exit]>
bash-3.00$
2. Silent Mode Installation(Using XML):(Depricated)
Though it is depricated it is simple and smooth to use. That makes still WLA love to use this method, So I want to do an experiment it
Set the classpath in .profile as shown below
export CLASSPATH=/export/home/wluser//bea/jdk150_10/jre/lib/rt.jar:/export/home/wluser/bea/weblogic92/server/lib/weblogic.jar:
export PATH=/export/home/wluser/bea/weblogic92/common/bin:$PATH
bash
1. Log in to the Windows system.
2. Create a silent.xml file that defines the configuration settings normally entered by a user during an interactive installation process, such as graphical-mode or console-mode
Get the sample silent.xml form the below bea site
http://e-docs.bea.com/common/docs92/install/scripts/silent.xml
Note:Please keep (<)open and close(/>) tags in every line in the xml
becuase removed that not displaying the xml content in the blog

?xml version="1.0" encoding="UTF-8"?
bea-installer # open tag
input-fields # open tag
data-value name="BEAHOME" value="/export/home/wluser/bea"
data-value name="USER_INSTALL_DIR" value="/export/home/wluser/bea/weblogic92"
data-value name="INSTALL_MERCURY_PROFILING_TOOLS" value="true"
data-value name="COMPONENT_PATHS" value="WebLogic Server/Server"
data-value name="INSTALL_SHORTCUT_IN_ALL_USERS_FOLDER" value="yes"
input-fields #close tag
bea-installer #close tag

./server922_solaris32.bin -mode=silent -silent_xml=silent1.xml -Djava.io.tmpdir=/tmp -log=/export/home/wluser/logs/BEA_install.log

To enable NodeManager following silent script can be used:
Note:Please keep (<)open and close(/>) tags in every line in the xml
becuase removed that not displaying the xml content in the blog
?xml version="1.0" encoding="UTF-8"?
bea-installer #open tag
input-fields #Open tag
data-value name="BEAHOME" value="/home/wluser/bea"
data-value name="USER_INSTALL_DIR" value="/home/wluser/bea/weblogic92"
data-value name="INSTALL_MERCURY_PROFILING_TOOLS" value="true"
data-value name="INSTALL_NODE_MANAGER_SERVICE" value="yes"
data-value name="NODEMGR_PORT" value="5513"
data-value name="COMPONENT_PATHS" value="WebLogic Server/Server"
data-value name="INSTALL_SHORTCUT_IN_ALL_USERS_FOLDER" value="yes"
input-fields #closing tag
bea-installer #closing tag

The explanation of the above command:
1.To install the Bea in Silent mode , we need to specify the arguments as "-mode=silent"
2.and Specify the silent.xml path
Silent.xml contains, the BEA Home path,Installation Directory path,Need to specify which component need to install
3.Optionally we can specify the path for the temp directory for extracting the compressed jars
4.Optionally we can specify the log path which can be used for the Tracing the installation errors or exceptions.


Final Overview Steps for installation:
--This is taken from one of blog

Oracle WebLogic Server is J2EE Server (earlier known as BAEWebLogic Server) similar to Oracle Application Server.
This post covers installation of Oracle WebLogic Server with available installation Mode and Components.
You can download Oracle WebLogic Software from here (Currently it is available on Windows, Linux and Solaris and can be installed on Windows Vista also)
A. Installation Mode
BEA products can be installed in following mode
i) Graphical Mode - Interactive GUI based
ii) Console Mode - Interactive Text Based (-mode=console)
iii) Silent Mode- Non Interactive method using XML properties file (-mode=silent -silent_xml=properties_xml_file)
.
B. Installation Type
i) Complete or
ii) Custom
.
C. Installation Component
Depending on type of installer you choose, you get following kind of component
1) WebLogic Server
—Server
—Server Examples
—Server Add-ons
2) Workshop
—Workshop for WebLogic
—Workshop Runtime Framework
3) WebLogic Integration
—Integration Server
—Workshop Integration Extension
—Integration Examples
4) WebLogic Portal
—Portal Server
—Workshop Portal Extension
—Portal Examples
.
D. Installation Requirement

i) Hard Disk- Approx 3.5 GB for complete installation.
ii) Memory - Minimum 1GB as per documentation (will work on 500MB as well)
iii) JDK - JDK (Java Development Kit - Not required on windows on Unix install JDK 4,5 or 6)
iv) BEA HOme Directory - This directory is repository for common files used by multiple BEA products.
v) Product Installation Directory- Specific to particular BEA product like WebLogic Server, Workshop for WebLogic, WEbLogic Integration …
vi) Temp Directory - approx 2.5 times of total installation (this will be cleaned up after installation)
.
E. Things to consider
1. Try NOT to give space in directory for BEA_HOME (like Program Files)
2. Try Not to exceed 12 characters when naming BEA_HOME
3. You can specifiy installation log file during installation like -log=/myinstalllog.log
4. To start installation in console mode use -mode=console
5. To start in silent mode, create silent.xml file containing all values and use -mode=silent -silent_xml=
.
F. Installation Steps
1. Welcome
2. Choose BEA Home
3. Choose Install Type (Complete , Custom). If you selected Custom, Go to 4 else go to 5
4. Choose Product and Component (mentioned in step C above)
5. Choose Product Installation Directories
6.Install Windows SErvice (only if installation is on windows AND You have administrative privileges AND this is first installation AND this is CUSTOM installation)
7. Installation complete
.
Start Installation on Windows/Linux
Go to location where you have download software and start installation as
server1001_win32.exe -mode=console -log=c:\weblogic.log
Replace server1001_win32.exewith executable name on Linux/Solaris and change location to directory as per Unix like /home/bea/weblogic.log (This will install BEA in interactive console mode)
.
References
Oracle WebLogic 10.2 Installation Guide

JVM Troubleshooting Tools

JVM Troubleshooting Tools:
If you look at Java tools section of the JDK 1.5 documentation page, you will see a group of new experimental tools called
"Troubleshooting Tools":
"jinfo": Prints configuration information for a given JVM process or a Java core file on the local machine or on a remote
machine through a debug server.
"jhat" - Heap Dump Browser: Starts a Web server on a Java heap dump file (eg, produced by "jmap -dump"), allowing the heap to
be browsed.
"jmap" - Memory Map: Prin00:24 10-01-2010ts shared object memory maps or heap memory details of a given JVM process or a Java
core file on the local machine or on a remote machine through a debug server.
"jsadebugd" - Serviceability Agent Debug Daemon: Attaches to a JVM process or a Java core file and acts as a debug server for
remote tools to connect.
"jstack" - Stack Trace: Prints a stack trace of threads for a given JVM process or a Java core file on the local machine or
on a remote machine through a debug server.
Note that not all functions described above are available on Windows systems. See next sections on how to use those tools
provided in JDK 1.6 on a Windows system.
1)'jinfo' - VM Option Value Checker
The first JVM troubleshooting tool I want try is the "jinfo" tool.
The "jinfo" tool included in the Windows version of JDK 1.6 only supports functions to view and modify HotSpot VM options of
the specified JVM process. Here is the "jinfo" command syntax:
C:\Pani>\Progra~1\java\jdk1.6.0_02\bin\jinfo
Usage: jinfo (to connect to a running process)
where is one of: -flag to print the value of the named VM option -flag [+-] to enable or disable the named VM option -flag = to set the named VM option to the given value -h -help to print this help message
HotSpot VM supports many options as described on the "Java HotSpot VM Options" page. You can change the default value of any
HotSpot VM option using the "-XX:..." command option when running the "java" command.
Here is a tutorial example of how to use the "jinfo" tool get the current value of a given VM option:
C:\Pani>\Progra~1\java\jdk1.6.0_02\bin\java -jar "\Program Files\java\jdk1.6.0_02\demo\jfc\Notepad\notepad.jar" (Notepad started.)
(Start another command window.)C:\Pani>\Progra~1\java\jdk1.6.0_02\bin\jps -l -m
424 \Program Files\java\jdk1.6.0_02\demo\jfc\Notepad\notepad.jar3984 sun.tools.jps.Jps -l -m
C:\Pani>\Progra~1\java\jdk1.6.0_02\bin\jinfo -flag ThreadStackSize 424
-XX:ThreadStackSize=0
Note that:
The "jps" tool is used to get the process ID (pid) of the Notepad JVM: 424. The output of the "jinfo" command shows that the current value of the ThreadStackSize option is 0 in the Notepad JVM.
Changing HotSpot VM Option using 'jinfo'
The "jinfo" tool can be used to view the current value of any HotSpot VM option of a given JVM process as described in the
previous section.
The "jinfo" tool can also be used set a new value of any HotSpot VM option using the "jinfo -flag name=value" format. Here is
what I did to test this function with JDK 1.6 on a Windows system:
C:\Pani>\Progra~1\java\jdk1.6.0_02\bin\java -XX:ThreadStackSize=512 -jar "\Program Files\java\jdk1.6.0_02\demo\jfc\Notepad\notepad.jar" (Notepad started)
(Start another command window.)C:\Pani>\Progra~1\java\jdk1.6.0_02\bin\jps -l -m
1424 \Program Files\java\jdk1.6.0_02\demo\jfc\Notepad\notepad.jar3124 sun.tools.jps.Jps -l -m
C:\Pani>\Progra~1\java\jdk1.6.0_02\bin\jinfo -flag ThreadStackSize 1424
-XX:ThreadStackSize=512
C:\Pani>\Progra~1\java\jdk1.6.0_02\bin\jinfo -flag ThreadStackSize=1024 1424 Exception in thread "main" java.io.IOException: Command failed in target VM at sun.tools.attach.WindowsVirtualMachine.execute (WindowsVirtualMachine.java:94) at sun.tools.attach.HotSpotVirtualMachine.executeCommand (HotSpotVirtualMachine.java:195) at sun.tools.attach.HotSpotVirtualMachine.setFlag (HotSpotVirtualMachine.java:172) at sun.tools.jinfo.JInfo.flag(JInfo.java:105) at sun.tools.jinfo.JInfo.main(JInfo.java:58)
Apparently, the target VM (the Notepad VM) does not allow me to change its option. I do not know why?
2)'jstack' - Stack Tracer of JVM Threads:
"jstack": A JVM troubleshooting tool that prints stack traces of all running threads of a given JVM process, a Java core
file, or remote debug server. The "jstack" tool included in the JDK 1.6 Windows version only supports limited functions as
shown the this help message:
C:\Pani>\Progra~1\java\jdk1.6.0_02\bin\jstack -help
Usage: jstack [-l] (to connect to running process)
Options: -l long listing. Prints additional information about locks -h or -help to print this help message
In order to test "jstack", I used this simple Java program, LongSleep.java: class LongSleep { public static void main(String[] a) { Runtime rt = Runtime.getRuntime(); System.out.println(" Free memory: " + rt.freeMemory()); System.out.println("Total memory: " + rt.totalMemory()); try {Thread.sleep(1000*60*60);} catch (InterruptedException e) {} }}
When LongSleep.java is running, I used "jps" to get its JVM process ID, pid. Then I ran "jstack" with that pid to get the
following stack information:
C:\Pani>\Progra~1\java\jdk1.6.0_02\bin\javac LongSleep.java
C:\Pani>\Progra~1\java\jdk1.6.0_02\bin\java LongSleep Free memory: 4997104Total memory: 5177344
(Start another command window.)C:\Pani>\Progra~1\java\jdk1.6.0_02\bin\jps -l -m3296 LongSleep2224 sun.tools.jps.Jps -l -m
C:\Pani>\Progra~1\java\jdk1.6.0_02\bin\jstack 3296
Full thread dump Java HotSpot(TM) Client VM (1.6.0_02-b06 mixed mod...
"Low Memory Detector" daemon prio=6 tid=0x02a7c800 nid=0xf20 runnable java.lang.Thread.State: RUNNABLE
"CompilerThread0" daemon prio=10 tid=0x02a78000 nid=0xb3c waiting ... java.lang.Thread.State: RUNNABLE
"Attach Listener" daemon prio=10 tid=0x02a76c00 nid=0x37c waiting ... java.lang.Thread.State: RUNNABLE
"Signal Dispatcher" daemon prio=10 tid=0x02a75c00 nid=0xd7c runnable java.lang.Thread.State: RUNNABLE
"Finalizer" daemon prio=8 tid=0x02a71400 nid=0x2e8 in Object.wait() java.lang.Thread.State: WAITING (on object monitor) at java.lang.Object.wait(Native Method) - waiting on <0x22990b38> (a java.lang.ref.ReferenceQueue$Lock) at java.lang.ref.ReferenceQueue.remove(ReferenceQueue.java:116) - locked <0x22990b38> (a java.lang.ref.ReferenceQueue$Lock) at java.lang.ref.ReferenceQueue.remove(ReferenceQueue.java:132) at java.lang.ref.Finalizer$FinalizerThread.run(Finalizer.java:159)
"Reference Handler" daemon prio=10 tid=0x02a6d000 nid=0xfbc in Obje... java.lang.Thread.State: WAITING (on object monitor) at java.lang.Object.wait(Native Method) - waiting on <0x22990a38> (a java.lang.ref.Reference$Lock) at java.lang.Object.wait(Object.java:485) at java.lang.ref.Reference$ReferenceHandler.run(Reference.java:116) - locked <0x22990a38> (a java.lang.ref.Reference$Lock)
"main" prio=6 tid=0x00296000 nid=0xef4 waiting on condition [0x0090... java.lang.Thread.State: TIMED_WAITING (sleeping) at java.lang.Thread.sleep(Native Method) at LongSleep.main(LongSleep.java:10)
"VM Thread" prio=10 tid=0x02a63c00 nid=0xc70 runnable
"VM Periodic Task Thread" prio=10 tid=0x02a7e000 nid=0xdd0 waiting ...
JNI global references: 571
Cool. Now I know how many threads are running inside a JVM, 8 of them. But my Java application, LongSleep, only runs under 1
thread named as "main", which is in a state called, TIMED_WAITING. This matches my expectation.
Java Thread Deadlock Demo Program:
In the previous section, "jstack" was used to print stack traces of all running threads of a given JVM process. But "jstack"
can also be used to detect deadlocks inside a given JVM process. The tutorial example below shows you how "jstack" prints
deadlock information:
1. Copy and save this Java program, import java.util.*;public class SimpleDeadLock extends Thread { public static Object l1 = new Object(); public static Object l2 = new Object(); private int index; public static void main(String[] a) { Thread t1 = new Thread1(); Thread t2 = new Thread2(); t1.start(); t2.start(); } private static class Thread1 extends Thread { public void run() { synchronized (l1) { System.out.println("Thread 1: Holding lock 1..."); try { Thread.sleep(10); } catch (InterruptedException e) {} System.out.println("Thread 1: Waiting for lock 2..."); synchronized (l2) { System.out.println("Thread 2: Holding lock 1 & 2..."); } } } } private static class Thread2 extends Thread { public void run() { synchronized (l2) { System.out.println("Thread 2: Holding lock 2..."); try { Thread.sleep(10); } catch (InterruptedException e) {} System.out.println("Thread 2: Waiting for lock 1..."); synchronized (l1) { System.out.println("Thread 2: Holding lock 2 & 1..."); } } } }}
2. Compile and run SimpleDeadLock.java. A deadlock will be created immediately between two running threads:
C:\Pani>\Progra~1\java\jdk1.6.0_02\bin\javac SimpleDeadLock.java
C:\Pani>\Progra~1\java\jdk1.6.0_02\bin\java SimpleDeadLock
Thread 1: Holding lock 1...Thread 2: Holding lock 2...Thread 2: Waiting for lock 1...Thread 1: Waiting for lock 2...
This deadlock is expected - Thread 1 is holding lock 1 and waiting for lock 2, while thread 2 is holding lock 2 and waiting
for lock 1.
See the next section on how to use "jstack" to print the deadlock information and stack traces of 2 related threads.
Detecting Java Thread Deadlocks with 'jstack':

With the deadlock demo program, SimpleDeadLock.java, running in a locked status as described in the previous section, I am
ready to run "jstack" to print the deadlock information and stack traces of 2 locked threads:
C:\Pani>\Progra~1\java\jdk1.6.0_02\bin\jps -l -m1464 SimpleDeadLock464 sun.tools.jps.Jps -l -m
C:\Pani>\Progra~1\java\jdk1.6.0_02\bin\jstack 1464
Full thread dump Java HotSpot(TM) Client VM (1.6.0_02-b06 mixed mod...
"DestroyJavaVM" prio=6 tid=0x00296000 nid=0x198 waiting on conditio... java.lang.Thread.State: RUNNABLE
"Thread-1" prio=6 tid=0x02a99c00 nid=0xee0 waiting for monitor entr... java.lang.Thread.State: BLOCKED (on object monitor) at SimpleDeadLock$Thread2.run(SimpleDeadLock.java:37) - waiting to lock <0x229bd238> (a java.lang.Object) - locked <0x229bd240> (a java.lang.Object)
"Thread-0" prio=6 tid=0x02a99000 nid=0xefc waiting for monitor entr... java.lang.Thread.State: BLOCKED (on object monitor) at SimpleDeadLock$Thread1.run(SimpleDeadLock.java:24) - waiting to lock <0x229bd240> (a java.lang.Object) - locked <0x229bd238> (a java.lang.Object)
"Low Memory Detector" daemon prio=6 tid=0x02a7c800 nid=0xd2c runnab... java.lang.Thread.State: RUNNABLE
"CompilerThread0" daemon prio=10 tid=0x02a78000 nid=0x500 waiting o... java.lang.Thread.State: RUNNABLE
"Attach Listener" daemon prio=10 tid=0x02a76c00 nid=0x32c waiting o... java.lang.Thread.State: RUNNABLE
"Signal Dispatcher" daemon prio=10 tid=0x02a75c00 nid=0x190 runnabl... java.lang.Thread.State: RUNNABLE
"Finalizer" daemon prio=8 tid=0x02a6e000 nid=0xdb0 in Object.wait()... java.lang.Thread.State: WAITING (on object monitor) at java.lang.Object.wait(Native Method) - waiting on <0x22990b38> (a java.lang.ref.ReferenceQueue$Lock) at java.lang.ref.ReferenceQueue.remove(ReferenceQueue.java:116) - locked <0x22990b38> (a java.lang.ref.ReferenceQueue$Lock) at java.lang.ref.ReferenceQueue.remove(ReferenceQueue.java:132) at java.lang.ref.Finalizer$FinalizerThread.run(Finalizer.java:159)
"Reference Handler" daemon prio=10 tid=0x02a6d000 nid=0xa44 in Obje... java.lang.Thread.State: WAITING (on object monitor) at java.lang.Object.wait(Native Method) - waiting on <0x22990a38> (a java.lang.ref.Reference$Lock) at java.lang.Object.wait(Object.java:485) at java.lang.ref.Reference$ReferenceHandler.run(Reference.java:116) - locked <0x22990a38> (a java.lang.ref.Reference$Lock)
"VM Thread" prio=10 tid=0x02a63c00 nid=0xe88 runnable
"VM Periodic Task Thread" prio=10 tid=0x02a7e000 nid=0xf58 waiting ...
JNI global references: 571
Found one Java-level deadlock:============================="Thread-1": waiting to lock monitor 0x02a6ee64 (object 0x229bd238, a java.lang.Object), which is held by "Thread-0""Thread-0": waiting to lock monitor 0x02a6eecc (object 0x229bd240, a java.lang.Object), which is held by "Thread-1"
Java stack information for the threads listed above:==================================================="Thread-1": at SimpleDeadLock$Thread2.run(SimpleDeadLock.java:37) - waiting to lock <0x229bd238> (a java.lang.Object) - locked <0x229bd240> (a java.lang.Object)"Thread-0": at SimpleDeadLock$Thread1.run(SimpleDeadLock.java:24) - waiting to lock <0x229bd240> (a java.lang.Object) - locked <0x229bd238> (a java.lang.Object)
Found 1 deadlock.
The output of "jstack" is very useful for debugging. It tells me:
How many deadlocks exist in this JVM process. What are the 2 waiting threads for each deadlock. Stack traces of waiting threads with source code line numbers, if source codes were compile with debug options.
'jmap' - JVM Heap Dump Tool:
"jmap" - Memory Map: Prints shared object memory maps or heap memory details of a given JVM process or a Java core file on
the local machine or on a remote machine through a debug server. "jmap" supports several functions with these syntaxes:
jmap [ option ] pidjmap [ option ] executable corejmap [ option ] [server-id@]remote-hostname-or-IP
When no option is used jmap prints shared object mappings. For each shared object loaded in the target VM, start address, the size of the mapping, and the full path of the shared object file are printed. This is similar to the Solaris pmap utility.
-dump:[live,]format=b,file= Dumps the Java heap in hprof binary format to filename. The live suboption is optional. If specified, only the live objects in the heap are dumped. To browse the heap dump, you can use jhat (Java Heap Analysis Tool) to read the generated file.
-finalizerinfo Prints information on objects awaiting finalization.
-heap Prints a heap summary. GC algorithm used, heap configuration and generation wise heap usage are printed.
-histo[:live] Prints a histogram of the heap. For each Java class, number of objects, memory size in bytes, and fully qualified class names are printed. VM internal class names are printed with '*' prefix. If the live suboption is specified, only live objects are counted.
-permstat Prints class loader wise statistics of permanent generation of Java heap. For each class loader, its name, liveness, address, parent class loader, and the number and size of classes it has loaded are printed. In addition, the number and size of interned Strings are printed.
-F Force. Use with jmap -dump or jmap -histo option if the pid does not respond. The live suboption is not supported in this mode.
But the "jmap" tool included in the Windows version of JDK 1.6 only supports functions to print histogram of Java object heap
and generate a heap dump of a given JVM process:
C:\Pani>\Progra~1\java\jdk1.6.0_02\bin\jmap
Usage: jmap -histo (to print histogram of java object heap of the JVM process) jmap -dump: (to dump java heap of the JVM process)
dump-options: format=b binary default file= dump heap to
Example: jmap -dump:format=b,file=heap.bin
See the next section on how to use "jmap" to print heap histogram and to generate heap dump.
Printing Histogram of Java Object Heap:
The first function of the "jmap" tool is to print histogram of object heap of a given JVM process. Now I am going to use a
sample Java program, GarbageCollection.java, I wrote in another tutorial example in this book.
The first test is to print the heap histogram of a JVM process that runs GarbageCollection.java with the "jmap -histo pid"
command:
C:\Pani>\Progra~1\java\jdk1.6.0_02\bin\javac GarbageCollection.java
C:\Pani>\Progra~1\java\jdk1.6.0_02\bin\java -Xms24m -Xmx24m GarbageCollection
Free/total memory:23725256 2503475222710400 2503475221618728 2503475220523584 25034752...
(Start another command window.)C:\Pani>\Progra~1\java\jdk1.6.0_02\bin\jps -l -m
492 sun.tools.jps.Jps -l -m428 GarbageCollection
C:\Pani>\Progra~1\java\jdk1.6.0_02\bin\jmap -histo 428
num #instances #bytes class name-------------------------------------- 1: 23 4723136 [I 2: 19 4718928 [J 3: 18 4718880 [D 4: 73925 1774200 java.lang.String 5: 208 1226400 [C 6: 28 1205064 [B 7: 18 1179936 [F 8: 68 297040 [Ljava.lang.String; 9: 332 14136 [Ljava.lang.Object; 10: 32 10240 11: 42 4032 java.lang.Class 12: 58 1392 java.util.Hashtable$Entry 13: 16 1280 [Ljava.util.HashMap$Entry; 14: 27 1000 15: 6 864 [S 16: 7 680 [Ljava.util.Hashtable$Entry; 17: 11 616 java.net.URL 18: 19 608 java.util.Locale 19: 5 560 java.lang.Thread 20: 14 560 java.util.HashMap...
The histogram gives a very good summary of heap objects used in my GarbageCollection.java program:
Most of the objects were String objects. There were 73925 of them. This matches well with what I allocated in the program:
one array of 64*64 string objects for each 1-MB object. If 16 1-MB objects were allocated, there should be 65536 string
objects. "[Ljava.lang.String;" is a special class name representing a java.lang.String[] array. "[I" is a special class name representing a int[] array.
Generating Heap Dump File with 'jmap':
The second function of the "jmap" tool is to generate a heap dump of a given JVM process with the "jmap -
dump:file=" command:
C:\Pani>\Progra~1\java\jdk1.6.0_02\bin\java -Xms24m -Xmx24m GarbageCollection
Free/total memory:23725256 2503475222710400 2503475221618728 2503475220523584 25034752...
(Start another command window.)C:\Pani>\Progra~1\java\jdk1.6.0_02\bin\jps -l -m
764 GarbageCollection1204 sun.tools.jps.Jps -l -m
C:\Pani>\Progra~1\java\jdk1.6.0_02\bin\jmap -dump:file=GarbageCollection.map 764
Dumping heap to C:\Pani\GarbageCollection.map ...Heap dump file created
C:\Pani>dir *.map
12:08 19,816,895 GarbageCollection.map
So the heap dump file, "GarbageCollection.map", is a snapshot of all heap objects used by the running GarbageCollection.java
process.
Heap dump files can be browsed by the heap dump browser, "jhat", as described in the next section.
'jhat' - Java Heap Analysis Tool :
"jhat" - Java heap analysis tool or heap dump file browser: Parses a Java heap dump file and launches a Web server. "jhat"
enables you to browse heap dump files 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 available at
http://localhost:7000/oqlhelp/
But the "jmap" tool included in the Windows version of JDK 1.6 only supports functions to print histogram of Java object heap
and generate a heap dump of a given JVM process:
C:\Pani>\Progra~1\java\jdk1.6.0_02\bin\jhat -help
Usage: jhat [-stack ] [-refs ] [-port ] [-baseline ] [-debug ] [-version] [-h-help]
-stack false Turn off tracking object allocation call stack. -refs false Turn off tracking of references to objects -port Set the port for the HTTP server. Default is 7000. -exclude Specify a file that lists data members that should be excluded from the reachableFrom query. -baseline Specify a baseline object dump. Objects in both heap dumps with the same ID and same class will be marked as not being "new". -debug Set debug level. 0: No debug output 1: Debug hprof file parsing 2: Debug hprof file parsing, no server -version Report version number -h-help Print this help and exit The file to read
For a dump file that contains multiple heap dumps,you may specify which dump in the fileby appending "#" to the file name, i.e. "foo.hprof#3".
All boolean options default to "true"


Starting 'jhat' Web Server on a Heap Dump File:
In an earlier tutorial example, I created a Java heap dump file with the "jmap" tool on my GarbageCollection.java program.
The heap dump file is named as GarbageCollection.map. Now I want to try to run the "jhat" Web server on this dump file and
browse the heap dump with a Web browser.
1. Run the "jhat" command with default options:
C:\Pani>\Progra~1\java\jdk1.6.0_02\bin\jhat GarbageCollection.map
Reading from GarbageCollection.map...Dump file created Jan 1 00:08:10 EDT 2008Snapshot read, resolving...Resolving 67324 objects...Chasing references, expect 13 dots.............Eliminating duplicate references.............Snapshot resolved.Started HTTP server on port 7000Server is ready.
2. Run a Web browser with http://localhost:7000/. The "jhat" heap dump file server page shows up:
See next sections on how to use "jhat" Web server to browse heap objects.
Listing Instance Counts of All Classes :
Running "jhat" Web server on a heap dump file offers us a very good debugging tool. You can get statistical counts of loaded
classes and objects. You can review object contents and references. You can also run object queries to search for any
specific information.
First, let's see how to get instance counts for all loaded classes.
1. Run a Web browser with http://localhost:7000/. The heap dump first page shows up.
2. Click the link of "Show instance counts for all classes (including platform)". The instance count page shows up:
65733 instances of class java.lang.String 362 instances of class java.lang.Class 330 instances of class [Ljava.lang.Object; 206 instances of class [C 66 instances of class [Ljava.lang.String; 58 instances of class java.util.Hashtable$Entry 50 instances of class [I 26 instances of class [B 19 instances of class java.util.Locale 19 instances of class java.util.concurrent.ConcurrentHashMap$HashEntry 17 instances of class [J 16 instances of class java.util.HashMap$Entry 16 instances of class java.util.concurrent.ConcurrentHashMap$Segment 16 instances of class java.util.concurrent.locks.ReentrantLock$NonfairSync 16 instances of class [D 16 instances of class [F 16 instances of class [Ljava.util.HashMap$Entry; 16 instances of class [Ljava.util.concurrent.ConcurrentHashMap$HashEntry; 14 instances of class java.lang.Object 14 instances of class java.util.HashMap 14 instances of class java.util.LinkedHashMap$Entry 12 instances of class java.io.ExpiringCache$Entry 11 instances of class java.net.URL 10 instances of class java.io.ObjectStreamField ....
The output shows that the highest count is the number of java.lang.String instances. This is expected, because I created
String arrays with 64*64 Strings in each array.
Browsing Object Instance Values:
After looking object instance counts, I want to find some object instances created by my program and browse their values. My
program, GarbageCollection.java, used the following code to create many java.lang.Object[] instances:
private static Object getOneMega() { Object[] lst = new Object[10]; lst[0] = new long[256*128]; lst[1] = new int[256*256]; lst[2] = new double[256*128]; lst[3] = new float[64*256]; lst[4] = new byte[64*1024]; String[] l = new String[64*64]; for (int i=0; i<64*64; i++) l[i] = new String("12345678"); // 16B lst[5] = l; lst[6] = new char[64*512]; return lst; } I want to find one of these Object[] instances and review its elements. 1. Run a Web browser with http://localhost:7000/. The heap dump first page shows up.
2. Click the link of "Show instance counts for all classes (including platform)". The instance count page shows up.
3. Click the link of "instances" in the line of "330 instances of class [Ljava.lang.Object;". Remember that
"[Ljava.lang.Object;" is the class name for Object[] arrays. A list of all 330 instances is displayed with their addresses.
3. Click on the first instance of "[Ljava.lang.Object;@0x25a9e6d0 (48 bytes)". The contents of this instance show up:
Object at 0x25a9e6d0
Array of 10 objects
Class:class [Ljava.lang.Object;
Values0 : [J@0x25aaea00 (262152 bytes) 1 : [I@0x25aeea10 (262152 bytes) 2 : [D@0x25b2ea20 (262152 bytes) 3 : [F@0x25b6ea30 (65544 bytes) 4 : [B@0x25b7ea40 (65544 bytes) 5 : [Ljava.lang.String;@0x25b8ea50 (16392 bytes) 6 : [C@0x25baa7b0 (65544 bytes) 7 : null8 : null9 : null
References to this object:[Ljava.lang.Object;@0x2536e920 (72 bytes) : Element 8 of [Ljava.lang.Object;@0x2536e920
Excellent! I am lucky that the first instance of Object[] is created by my code. "jhat" does a good job showing me everything
about this instance. I can continue clicking its values or references to get information.
Conclusion: "jhat" is much easier to use than many Java debugger for browser heap objects.
Object Query Language (OQL):
OQL (Object Query Language): A 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 [ from [instanceof] [ where ] ]
where class name is fully qualified Java class name (example: java.net.URL) or array class name. [C is char array name,
[Ljava.io.File; is name of java.io.File[] and so on. Note that fully qualified class name does not always uniquely identify a
Java class at runtime. There may be more than one Java class with the same name but loaded by different loaders. So, class
name is permitted to be id string of the class object. If instanceof keyword is used, subtype objects are selected. If this
keyword is not specified, only the instances of exact class specified are selected. Both from and where clauses are optional.
In select and (optional) where clauses, the expression used in JavaScript expression. Java heap objects are wrapped as
convenient script objects so that fields may be accessed in natural syntax. For example, Java fields can be accessed with
obj.field_name syntax and array elements can be accessed with array[index] syntax. Each Java object selected is bound to a
JavaScript variable of the identifier name specified in from clause.
OQL Examples:
select all Strings of length 100 or more: select s from java.lang.String s where s.count >= 100
select all int arrays of length 256 or more: select a from [I a where a.length >= 256
show content of Strings that match a regular expression: select s.value.toString() from java.lang.String s where /java/(s.value.toString())
show path value of all File objects: select file.path.value.toString() from java.io.File file
show names of all ClassLoader classes: select classof(cl).name from instanceof java.lang.ClassLoader cl
show instances of the Class identified by given id string: select o from instanceof 0xd404b198 o
Note that 0xd404b198 is id of a Class (in a session). This is found by looking at the id shown in that class's page.
See next section on how to run OQL statements on the "jhat" Web server.
Searching for Instances with OQL Statements:
To test the power of OQL, I want to find those Object[] instances created by my program, excluding Object[] created by the
JVM platform.
1. Run a Web browser with http://localhost:7000/. The heap dump first page shows up.
2. Click the link of "Execute Object Query Language (OQL) query". The OQL query page shows up.
3. Enter the following query and click the Execute button:
select i from [Ljava.lang.Object; i where i.length == 10
Cool. "jhat" returns a list of instances that matches my query condition:
But the previous OQL query is not good enough to return only Object[] instances I wanted. The query below will do a better
job. Try it.
select i from [Ljava.lang.Object; i where i.length == 10 && i[5] != null && classof(i[5]).name == '[Ljava.lang.String;'
Watch out the OQL statement syntax. It takes JavaScript expressions only, not SQL expressions.

Types of Clustering and WebLogic

Introduction to Clustering

The WebLogic Clusters offer a cost-effective, high-performance, and highly available architecture for the cluster-aware applications. There are many types of clusters in various environments, and capacity plannings. Generally, clusters are classified based on their functionality. Here I am breifly discussing about the types of clusters they are:

1. Failover Clusters
2. Scalable High Performance Clusters
3. Application Clusters
4. Network Load balancing clusters
5. Other types of clusters

Let us examine the similarities and differences of each class of clusters.

Failover Clusters
This class of cluster is the most widely used in today’s e-commerce environment. Sometimes they are also called HA clusters or segregated clusters. With this type, the emphasis is on complete avoidance of unplanned downtime and also on achieving high availability.

If one of the nodes in a cluster becomes unavailable, due to either planned downtime for maintenance or unplanned downtime due to failure, another node takes over to provide the service to the end-user—a process known as failover. When failover occurs, users who are accessing the cluster service continue to access the service, and are unaware that it is being provided from a different server (node). This architecture emphasizes the availability of the database or application service, rather than performance or load balancing.

High availability clusters
allow multiple servers, in conjunction with shared disk storage units, to quickly recover from failures. Hardware or software failures, affecting either a critical component or an entire system, trigger a failover from one system in the cluster to another. Application processing and access to disk-based data is typically restored within minutes, although recovery times vary depending upon the specific characteristics of the application and the system configuration.

Scalable High Performance Clusters
This class of cluster provides scalability, high-performance, load balancing, and high availability through the use of parallel middleware. These are also sometimes called parallel clusters or high performance computing clusters (HPCC). They provide a single system image, or in other words, the application can be executed on any of the servers within the cluster. They are used to execute compute-intensive and data-intensive problems by running the job on multiple nodes at the same time.

These clusters utilize parallel-aware software that breaks the task down into smaller chunks, which are dispatched across a network of interconnected systems. The network processes the chunks concurrently and communicates with the nodes using message-passing libraries to coordinate and synchronize the results. Cluster-aware applications take advantage of the network architecture in three ways:

• Parallel Computing, Multi-Threading, and Modularization
• Load Balancing
• Automatic Failure

Parallel database clusters like Oracle Real Application Clusters, IBM Sysplex Database Cluster, and Beowulf Computers fit into this group of clusters. Beowulf clusters are of particular interest to the scientific and educational communities. Beowulf clusters are built by using commodity systems – PCs, workstations, or servers running software such as Linux. They feature a parallel computing system consisting of multiple interconnected nodes and are able to execute parallel jobs.
Through message passing, nodes synchronize data and share results. Oracle RAC uses message passing to process requests and update data on each node, resulting in fast data access and a consistent database.

Application Server Clusters
Nodes running application server clusters are connected to provide availability and scalability. In this type of cluster, each node runs an instance of the application server. They run the application server independently from each other’s instance. There is no concept of failover. When clustered in this way, the state of certain objects is maintained synchronously. Web server clients can connect to either of the application server instances. Application servers such as WebLogic Server, Websphere, and Oracle Application server are examples of this category of clusters.

As an example, the WebLogic Server cluster consists of multiple copies of the WebLogic program running simultaneously and working together to provide increased scalability and reliability. The cluster appears to the web server clients as a single WebLogic Server instance. In WebLogic deployment, Servlets, JSPs, EJB, Remote Method Invocation (RMI) objects, Java Messaging Service (JMS) destinations, and Java Database Connectivity (JDBC) connections are usually clustered.

Clustering in J2EE, as in the Oracle Applications server, is implemented across a number of tiers, namely the client tier, Web tier, EJB tier, and EIS tier. Every tier has load balancing and failover.

Other Types of Clusters
The term cluster is loosely used to specify a condition when two networking components or two storage units are joined to provide backup and failover facility. Two or more clusters can also be located at remote locations and be linked to form a global cluster. Some of the other widely known clusters include:

• NetApp Filer Clusters
• Network Load Balancing Clusters
• Global Clusters