Tools and Utilities - Expert Oracle RAC Performance Diagnostics and Tuning - page 143

Oracle Enterprise Manager (OEM) comes in two flavors: Database Express, which is installed during the database
creation time with the database, and Cloud Control, which is a separate product that is installed and configured from
a set of DVD or installer. Cloud Control can be installed on the same node as the database server or can be installed
separately on another node (which is the preferred approach). EM Cloud Control is normally installed as two separate
tiers: the repository and the EM console/client. While the client is accessed through a browser, the repository can be
installed on most operating systems.
EM Cloud Control comprises a three-tier configuration: the target database that is controlled or monitored
through an EM agent process installed on all database servers; the middle tier or the Oracle Management
Server (OMS, also called the EM repository) where all the target database information is collected and stored; and
the client or console tier used to display the information. The repository is used to capture and store information
pertaining to the target tier.

■ the functionalities offered by database express are a subset of the eM Cloud Control and contain most of
the features with the exception of the oMs. database express also consists of an agent; however, the agent does not
communicate with any oMs not configured.

Note

The front tier is the console and is used to monitor the database (target tiers) via the management server. Storing
the information in the management server provides additional functionality, such as sending a page to a DBA when
any alert is encountered and collecting target tier statistics when the DBA is not monitoring the console for historical
information.
The target tier consists of the instance, the database, and the intelligent agent that runs in the background and
helps communicate database-related information back to the OMS. The intelligent agent also contains a data gatherer
that is used to gather data on a continuous basis.
Figure 6-1 illustrates the EM Cloud Control component architecture. It represents the three-tier configuration
consisting of the console or the user interface tier, the OMS tier or the middle tier, and the end tier or the target
tier. The target tier can consist of multiple databases servers, application servers, and web servers across one or
more locations that the EM Cloud Control will monitor and manage. A single EM Cloud Control configuration can
administer and manage several targets across different operating systems, and with the recent Oracle acquisitions,
it can administer and manage several types of applications using appropriate plug-ins.