d8888 888 888      88888888888 888      d8b                                 888       888          888       .d8888b.           888                               
      d88888 888 888          888     888      Y8P                                 888   o   888          888      d88P  Y88b          888                               
     d88P888 888 888          888     888                                          888  d8b  888          888      Y88b.               888                               
    d88P 888 888 888          888     88888b.  888 88888b.   .d88b.  .d8888b       888 d888b 888  .d88b.  88888b.   "Y888b.   88888b.  88888b.   .d88b.  888d888 .d88b.  
   d88P  888 888 888          888     888 "88b 888 888 "88b d88P"88b 88K           888d88888b888 d8P  Y8b 888 "88b     "Y88b. 888 "88b 888 "88b d8P  Y8b 888P"  d8P  Y8b 
  d88P   888 888 888          888     888  888 888 888  888 888  888 "Y8888b.      88888P Y88888 88888888 888  888       "888 888  888 888  888 88888888 888    88888888 
 d8888888888 888 888          888     888  888 888 888  888 Y88b 888      X88      8888P   Y8888 Y8b.     888 d88P Y88b  d88P 888 d88P 888  888 Y8b.     888    Y8b.     
d88P     888 888 888          888     888  888 888 888  888  "Y88888  88888P'      888P     Y888  "Y8888  88888P"   "Y8888P"  88888P"  888  888  "Y8888  888     "Y8888  
                                                                 888                                                          888                                        
                                                            Y8b d88P                                                          888                                        
                                                             "Y88P"                                                           888   

All Things WebSphere

Concerns and issues relating to all versions of WebSphere Application Server

Tuesday, January 31, 2012


Class loading and debugging class loader memory leaks in WebSphere Application Server

See this excellent presentation on Debugging Classloader leaks in application servers http://www.websphereusergroup.org.uk/wug/files/presentations/31/Ian_Partridge_-_WUG_classloader_leaks.pdf


WebSphere Classloader Memory Leak Prevention

Solving Application ClassLoader Leaks

Applications tend to want to:
  • Start new threads using Runnable implementations from the application class loader. Even though the JEE programming model does not support this, customers frequently either directly create new threads or indirectly create them by using Timers. Customers must ensure that these threads are stopped when the corresponding application (or WAR module) is stopped:
    • javax.servlet.ServletContextListener.contextDestroyed can be used to be notified when a WAR is being stopped in order to clean up. Note that WARs can be stopped independently from an application when class reloading is enabled.
    • javax.ejb.Singletonjavax.ejb.Startup, and javax.annotation.PreDestroy annotations can be used to be notified when an EJB module is being stopped in order to clean it up. Note, singleton EJBs are only available in EJB 3.1 (WAS v8).
    • Startup beans can be used to be notified when an EJB module is being stopped in order to clean up. All EJB modules are stopped when an entire application is being stopped.
  • Use ThreadLocal (storing a ThreadLocal in a static). ThreadLocal values are effectively stored as WeakHashMap in each Thread. Since the values typically include application objects, the application object references its Class, which references its ClassLoader, which references the Class contain the ThreadLocal, the weak reference is never broken, and a leak occurs.
    Customers are encouraged either to avoid the use of ThreadLocal, to clear references to the ThreadLocal when the module is stopped (see above), or to ensure that remove() is called after every request.
  • Register JMX MBeans or NotificationListener with the JMX server. Customers must ensure that these are unregistered when the corresponding application (or WAR module) is stopped.

Arbitrary components

This includes JDBC providers, third-party software, and applications themselvestend to want to:
  • Start new threads, including the "timer threads" created by the java.util.Timer constructor. When a Thread is created, two pieces of information are copied from the primordial thread:
    1. The context class loader (getContextClassLoader()). When an application is executing, the containers set the context class loader to the module class loader, so the newly created thread will keep the context class loader alive for the duration of its existence. This can be avoided by calling setContextClassLoader to a non-application class loader prior to starting the timer and then resetting it afterwards.
    2. The AccessControlContext of the calling thread (as documented by AccessController). If the thread is being started due to an API call from an application, then the application's ProtectionDomain will be in theAccessControlContext, and the ProtectionDomain of an application class will include a reference to its ClassLoader. This can be avoided by creating the thread using doPrivileged. Note that care must be taken to ensure that the use of doPrivileged does not allow unprivileged applications to create threads.

    For example:
    // doPrivileged fixes the AccessControlContext leak, and it is also required
    // for calls to Thread.get/setContextClassLoader.
    Timer timer = AccessController.doPrivileged(new PrivilegedAction() {
      public void run() {
        Thread thread = Thread.currentThread();
        ClassLoader savedCL = thread.getContextClassLoader();
        try {
          // The Timer constructor will create a Thread, which will copy the
          // context class loader from the current thread, which is now null.
          return new Timer(true);
        } finally {
  • Associate data with the current context class loader. This is typically done via a MapValue>. This Map must either:
    1. Have explicit lifecycle APIs. In this case, the lifecycle API must be called. If the code was introduced by a customer, then the customer is responsible for adding a JMX listener. If the code was introduced by a WAS prereq, then the owner must use a WAS application listener API. If the code belongs to the JDK, then the runtime team will accept responsibility for calling it (e.g., ResourceBundle.clearCache andIntrospector.flushCaches).
    2. Be a WeakHashMap to allow the ClassLoader key to be garbage collected. Note that the value must not hold a non-weak reference to classes or objects created from that ClassLoader, or the entry will never be removed. Either WeakHashMap<ClassLoader, WeakReference<Class>> or WeakHashMap<ClassLoader, Tuple>, where Tuple contains WeakReference<Class> and WeakReference<Object> to an object instantiated from the class. In both cases, the Class is held weakly, which will still allow the ClassLoader to be collected. In the latter case, the reference to the instantiated object will be cleared if a GC occurs, but the assumption is made that it can be cheaply reinstantiated.
These tips are courtesy of WAS guru Brett Kail


Monday, January 23, 2012


New Features in WebSphere Application Server version

WAS 8002 was available for general availability on 1/16/2012. The blog post below provides the necessary links for download and an overview and brief detail of the new features in WebSphere Application Server version Please note that a fix pack contains both features and APAR fixes.
WAS 8002 & other offerings download --> http://www-01.ibm.com/support/docview.wss?uid=swg24031368
Recommended Fixes Page --> http://www-01.ibm.com/support/docview.wss?rs=180&context=SSEQTP&uid=swg27004980#ver80
Readme --> http://www-01.ibm.com/support/docview.wss?uid=swg27023570
FixList 8002 -> http://www-01.ibm.com/support/docview.wss?uid=swg27022958
z/OS --> http://www-01.ibm.com/support/docview.wss?rs=404&uid=swg27006970

Improvements in WAS 8002  =>

Education on ALL these new features is provided by the IBM Education Assistant here 

Customized access logging for WAS 
Before V8.0.0.2 the access log only offered two options for format, common and combined. With  the new access log enhancements added in V8.0.0.2 you can customize how much information, and what information, is displayed. 17 directives were added to display different pieces of information in the access log. These directives, allow for any order the user wants and each directive can be quoted. These access log enhancements provide greater customization and more information on display to the user.

%h %u %t "%r" %s %b "%{Referer}i" "%{User-agent}i" "%C"
Remote host, URL path not including query string, start time of request (NCSA format), method, path, query-string, and protocol, ..... 

- Directives must be separated by spaces
- Individual directives can be surrounded by quotes
- Directives can be ordered however the user wishes
- Unless noted, all directives will print - if no value is found

� Information on access log functionality:
� Used as a base for the new functionality:

Tools from the Virtual Member Manager to clear adapter cache, manage realm default parent & retrieve the data model
  • The Clear Adapter Cache feature is needed to ensure that VMM always returns correct data.  Changes made to the existing Get and Search commands. New control added to be used with the existing Get and Search API. Two new commands added for handling the cache of the adapters. 
  • New commands for set, update, delete, list of realm level default parent. Simplifies configuration and management. Commands can be used in server and local mode
  • VMM data Model is a description of the organization of data in a manner that reflects the information structure supported by VMM. VMM allows to retrieve the different kinds of information related to its data model schema. To retrieve the VMM schema there is currently a supported API. There is no command used from the command line to retrieve the schema.This feature adds new commands to retrieve the different VMM data model that can be used in server and local mode.

Fixing the Performance problem with the Service Data Object (SDO) Repository
The feature focuses on enhancing the performance of the SDO repository. This is done by
changing the way in which the data is accessed by the entity beans. Finder methods fetches the entire objects even if you are interested in just one column in the table, these are exposed to the clients. Replacing the finder methods with the ejbSelect methods and exposing them to client interface enhances the performance by several factors.

sibDDLGenerator enhancements for SIBus - 
Before these enhancements, the sibDDLGenerator command created the CREATE DATABASE statement DDL and created the tablespaces listed here. If the same database had to be shared by multiple messaging engines, it was necessary  to make some changes to the DDLs generated by the sibDDLGenerator command:
remove the CREATE DATABASE statement DDL, and modify the tablespace names. As part of the enhancements to the sibDDLGenerator, two new parameters (-createdbstmt, -tablespaceprefix) are added.  These parameters remove the need for changes to the DDLs generated by the sibDDLGenerator command .

Installation changes and enhancements in IBM WebSphere Application Server V8.0 for the z/OS platform
Clarification of fix pack delivery mechanism (PTFs) to ensure fixed service footprint and Support for Installation Manager console mode



How to create a non-transactional JDBC connection in WAS

The ability to create a non-transactional datasource was introduced in WAS 7.0, and thus unavailable in any earlier release.

Answer: Courtesy of Fred Rowe  =>
  1. In the admin console, navigate to "Resources | JDBC | Data sources"
  2. Select the desired datasource from the list.
  3. Click on the "WebSphere Application Server data source properties" link to the right of the screen under the "Additional Properties" group.
  4. Check the "Non-transactional data source" box.
  5. Restart the server.



December 2006   September 2008   January 2009   February 2009   March 2009   September 2009   October 2009   November 2009   December 2009   January 2010   February 2010   March 2010   April 2010   October 2010   January 2011   February 2011   April 2011   May 2011   June 2011   July 2011   August 2011   September 2011   October 2011   November 2011   December 2011   January 2012   February 2012   March 2012   April 2012   May 2012   June 2012   July 2012   August 2012   September 2012   October 2012   November 2012   January 2013   May 2013   June 2013   July 2013   September 2013   October 2013   June 2014   August 2014  

This page is powered by Blogger. Isn't yours?

Subscribe to Posts [Atom]