What is the function of T3 in Weblogic server ?

T3 provides a framework for Weblogic server messages that support for enhancements. 

These enhancements include abbreviations and features, such as object replacement, that work in the context of Weblogic server clusters and HTTP and other product tunneling.

T3 predates Java Object Serialization and RMI, while closely tracking and leveraging these specifications.

T3 is a superset of Java Object.

Serialization or RMI; anything you can do in Java object serialization and RMI can be done over T3.

T3 is mandated between Weblogic Servers and between programmatic clients and a Weblogic server cluster.

HTTP and IIOP are optional protocols that can be used to communicate between other processes and Weblogic server.

It depends on what you want to do.

For example, when you want to communicate between a browser and Weblogic Server-use HTTP, or an ORB and Weblogic Server-IIOP.

How are notifications made when a server is added to a cluster ?

The Weblogic Server cluster broadcasts the availability of a new server instance each time a new instance joins the cluster.

Cluster-aware stubs also periodically update their list of available server instances.

How many Weblogic servers can I have on a multi-CPU machine ?

There are many possible configurations and each has its own advantages and disadvantages.

BEA Weblogic server has no built-in limit for the number of server instances that can reside in a cluster.

Large, multi-processor servers such as Sun Microsystems Inc. Sun Enterprise 10000, therefore, can host very large clusters or multiple clusters.

In most cases, Weblogic server clusters scale best when deployed with one Weblogic server instance for every two CPUs.

However, as with all capacity planning, you should test the actual deployment with your target web applications to determine the optimal number and distribution of server instances.

How do I provide user credentials for starting a server ?

When you create a domain, the Configuration Wizard prompts you to provide the username and password for an initial administrative user.

If you create the domain in development mode, the wizard saves the username and encrypted password in a boot identity file.

A Weblogic server instance can refer to a boot identity file during its startup process.

If a server instance does not find such a file, it prompts you to enter credentials.

If you create a domain in production mode, or if you want to change user credentials in an existing boot identity file, you can create a new boot identity file.

How should you type cast a remote object ? Why ?

A client program that is intended to be interoperable with all compliant EJB Container implementations must use the javax.rmi.PortableRemoteObject.narrow(?) method to perform type-narrowing of the client-side representations of the remote home and remote interfaces.

Programs using the cast operator for narrowing the remote and remote home interfaces are likely to fail if the Container implementation uses RMI-IIOP as the underlying communication transport.

How do you set the classpath ?

Weblogic Server installs the following script that you can use to set the classpath that a server requires : 

Windows

WL_HOME/server/in/setWLSEnv.cmd

xNIX

WL_HOME/server/bin/setWLSEnv.sh

How do stubs work in a Weblogic Server cluster ?

Clients that connect to a Weblogic server cluster and look up a clustered object obtain a replica-aware stub for the object.

This stub contains the list of available server instances that host implementations of the object.

The stub also contains the load-balancing logic for distributing the load among its host servers.

How can I set deployment order for applications ?

Weblogic server allows you to select the load order for applications.

Weblogic server deploys server-level resources (first JDBC and then JMS) before deploying applications.

Applications are deployed in this order: Connectors, then EJBs, then Web Applications.

If the application is an EAR, the individual components are loaded in the order in which they are declared in the application.xml deployment descriptor.

How do I increase Weblogic Server memory ?

Increase the allocation of Java heap memory for WebLogic Server.
(Set the minimum and the maximum to the same size.)

Start WebLogic Server with the -ms32m option to increase the allocation, as in this example : 

$ java ... -ms32m -mx32m ...

This allocates 32 megabytes of Java heap memory to WebLogic Server, which improves performance and allows WebLogic Server to handle more simultaneous connections.

You can increase this value if necessary.