Shared APPL_TOP and Application Tier Filesystem

In the Shared APPL_TOP feature introduced by Oracle in E-Business 11i, Oracle allows multiple nodes to share a single APPL_TOP .In a shared APPL_TOP configuration, the APPL_TOP and COMN_TOP file systems can be installed on a single shared disk. The shared disk resource can then be shared via various network file protocols across multiple nodes to provide standard application tier services such as forms, web and concurrent processing. A shared APPL_TOP also significantly simplifies the patching or upgrade process since it has to be performed only once and changes made are immediately visible to all the nodes.

Here it is important to note that there is a difference between a Shared APPL_TOP and a Shared Application Tier File system. In a Shared APPL_TOP though the APPL_TOP(APPL_TOP and the COMMON_TOP ) is shared across different nodes, each nodes still have their individual ORACLE_HOME. In a Shared Application Tier FileSystem both the APPL_TOP and the ORACLE_HOME (ORA_TOP) reside on the shared disk.

The Shared APPL_TOP architecture was introduced in 2003 however with the release of 11.5.10 Oracle has extended this feature to share the entire application tier filesystem thereby further reducing disk space and bring down maintenance tasks.This is what is referred to now as the Shared Application Tier File System.

This feature i found to be particularly useful if your oracle applications environment uses multiple languages. Using the Shares APPL_TOP feature i do not now have to apply the translation on all the application Tier nodes but just to the Shared APPL_TOP.

In both the cases any changes on the shared TOPs like for example patch application is immediately visible to all the nodes of the application tier.

Another important factor to be kept in mind is that SHARED APPL_TOPS will not work if different nodes are on different Operating systems. So its mandatory that the different nodes of the application tier run on a same operating system or in other words the different nodes must be binary compatible.

Also as of now the SHARED APPL_TOP feature is not available for the windows version of Oracle Applications.

Apart from reducing maintenance tasks a shared APPL_TOP/Shared Application Tier Filesystem also improves scalability of the system as it less complex to bring in an additional node to improve performance.

There are various methods by with you can implement shared APPL_TOP like using Rapid Install or by merging existing APPL_TOPs

It is mandatory for you to have implemented autoconfig before you can proceed with the implementation of a Shared APPL_TOP

The metalink note Sharing the Application Tier File System in Oracle Applications 11i 233428.1 talks about implementing shared APPL_TOP under different Scenarios

While patching a shared APP_TOP you can just apply the path to any of the nodes and it will become visible to all the nodes, in case of applying a patch to 8.0.6 home or IAS_HOME you need to apply the patch only once but to a primary node.

Shared APPL_TOP and Shared Application Files system concepts are different from a Staged APPL_TOP. A Staged APPL_TOP is implemented to reduce your patching related downtimes by creating a exact clone of your production system, patching that system and synchronizing your cloned at database and application level to the production system.

This approach significantly reduced your patching downtime.

To knopw more about a Staged APPL_TOP refer to metalink note 242480.1