Partitioning with Farms and Clusters Oracle Application Server Tips by Burleson Consulting

Now that we understand the basic configuration of multiple Oracle9iAS instance, it?s important to recognize the sub-partitioning within the App Server layer.  Oracle9iAS provides two levels of collections with the App Server layer, allowing the Oracle9iAS administrator flexibility in the creation of multiple Oracle9iAS instances:

• Instances - In Oracle9iAS, an instance is defined as a collection of processes required to run a component within an application server instance. A instance is made up of one or more Java containers and the support structure needed to support them.  The Oracle9iAS Infrastructure is an instance with a supporting database to store metadata.

• Clusters - In Oracle9iAS a ?cluster? is an arbitrary collection of instances that are part of the same farm and also shared a common configuration and J2EE applications.. 

• Farms - In Oracle9iAS, a ?farm? is a collection of instances and clusters that comprise your Oracle9iAS system and share a common repository infrastructure.

In sum, a farm is any related group of Oracle9iAS instances sharing a repository, while a cluster must share a common definition and J2EE applications (Figure 1.7).  Any Oracle9iAS architecture may have many farms and many clusters defined within the system.

Figure 7: Oracle9iAS Farms and Clusters

Now that we have the basic idea, let?s take a closer look at Farms and clusters.

Oracle9iAS Clusters

A cluster is a collection of Oracle9iAS instances that share identical configuration parameters an application deployment schemes and J2EE applications.  Clusters are used to enforce heterogeneity within the Oracle9iAS instances.  Hence, additions are commonly made to clusters when processing demands require an additional Oracle9iAS instances in order to manage an increased demand at the application server level.  Instances in a cluster are managed by the Oracle9i AS Infrastructure, which provides an easy method or creating and maintaining clusters.

It is important to note that Oracle9iAS clusters are used in conjunction with the Web Cache load balancing algorithms, such that the load balancing at the Web Cache layer monitors all of the Oracle9iAS instances in the clusters, and feeds work to the least-loaded Oracle9iAS instance.  Please note that only J2EE and Web Cache components can be clustered, and that clusters must host a common set of J2EE applications.

Oracle9iAS Farms

There is important one-to-many relationship between an Oracle9iAS instance and a metadata repository.  Each Oracle9iAS instance may have one, and only one metadata repository, while each metadata repository may service many Oracle9iAS instances. 

From the Oracle9iAS architecture point of view, a farm is a collection of Oracle9iAS instances is that all map to the same metadata repository. Because each Oracle9iAS instance within a farm must contain the same metadata repository, all instances within the farm must share of the same configuration and application membership information.

Now that we understand the App server level, let?s take a quick look at the database tier of Oracle9iAS.

The Oracle9iAS Database Tier

The Oracle9iAS database tier contains the standard Oracle9i relational database (or any other database).  The function of the database tier is to provide the application with persistent storage.  The Oracle9i Application Server also contains a special instance called the Infrastructure that uses a 9i database to store metadata.  This database is more correctly in the application server tier since it does not provide persistent storage for the application.  The application server provides a method to place the Infrastructure database schema into a database in the database tier however best practices will still recommend that the Infrastructure database support only the infrastructure and to be seterate from the customer database for performance reasons.

• Oracle Portal ? Oracle web screen component definitions are stored inside the Oracle infrastructure database.

• Oracle Reports ? Oracle report specifications are stored inside the Oracle infrastructure database.

• Oracle Discoverer ? Oracle discoverer metadata is stored inside the infrastructure.

• Oracle Personalization ? The Oracle infrastructure database is used to store consumer group information and historical page viewing (referrer statistics) information.

Now that we have covered the database tier, let?s dive deeper into the Oracle9iAS architecture and take a brief tour of each of the Oracle9iAS components.

Oracle9iAS Component Overview

Let?s begin out tour of Oracle9iAS with a brief review of the component pieces of Oracle9iAS.  It is important to note that not all shops will have all of these components installed, but Oracle9iAS allows for any or all of these components to be created inside the architecture. 

This is an excerpt from "Oracle 10g Application Server Administration Handbook" by Don Burleson and John Garmany.