Oracle Enterprise Manager (OEM or EM) is a set of web-based tools aimed at managing software and hardware produced by Oracle Corporation as well as by some non-Oracle entities.

Oracle Enterprise Manager Grid Control is used for managing lots of databases and application servers.
It can manage multiple instances of Oracle deployment platforms; the most recent edition also allows for management and monitoring of other platforms such as Microsoft .NET, Microsoft SQL Server, NetApp Filers, BEA weblogic and others.
Partners and IT organizations can build extensions to Oracle Enterprise Manager, and make them available to other Enterprise Manager users via Oracle Enterprise Manager Grid Control Extensions Exchange.
Oracle Enterprise Manager provides comprehensive, flexible, easy-to-use monitoring functionality that supports the timely detection and notification of impending IT problems to the intended users. It offers the most comprehensive monitoring from Oracle Database instances to Oracle Real Application Clusters to Oracle Application Server Farms and Clusters.
OEM Grid Control comes with a comprehensive set of performance and health metrics that allow monitoring of key components in your environment such as applications, application servers, databases, as well as the back-end components on which they rely, such as hosts, operating systems and storage.
The architecture of the OEM for Grid Control has three distinct components:

  • the collection agent (Oracle Management Agent or OMA)
  • the aggregation agent (Oracle Management Server or OMS)
  • the repository agent (Oracle Management Repository or OMR)
    The OMA runs on the target host and collects information on the hardware, operating system, and applications that run on the target. The OMS runs on one or two servers and collects the data generated by the OMAs. The OMS pulls the information from the OMAs and aggregates the collections into the repository. The OMS also acts as the user-interface — by generating web-pages for database administrators to view the status of systems and services. The OMR comprises an instance of the Oracle database that stores the data collected by the OMS. Installers can make the OMR highly available or fault-tolerant by running it on an Oracle RAC instance across multiple nodes.

    Oracle Enterprise Manager performs much of its activity through intelligent agents which Oracle Corporation refers to as Oracle Management Agents. These run as autonomous proxy processes on a managed node, and perform execution and monitoring tasks for Oracle Enterprise Manager, communicating using the Hypertext Transfer Protocol (HTTP or HTTPS).