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Oracle9i Real Application Clusters Real Application Clusters Guard I - Concepts and Administration
Release 2 (9.2)

Part Number A96601-01
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cluster manager

An platform-specific component that discovers and tracks the membership state of each node by providing a common view of cluster membership across the cluster. The cluster manager also monitors process health, specifically the health of the database instance.

customer query

A PL/SQL procedure containing a query that should represent the actual work that must be done in the instance. The purpose of the customer query is to determine whether the primary instance is capable of work. The customer modifies the PL/SQL procedure that is provided in the Oracle Real Application Clusters Guard catpfs.sql script.


The means of failure recognition and recovery used by Real Application Clusters.

fault tolerance

The ability of a system or component to continue normal operation despite the presence of hardware or software faults. This normally involves some degree of redundancy.

foreign node

The node where a pack runs when it is not running on its default (home node). When a pack is running on its foreign node, only the IP address is configured to be up.


See high availability.

hardware failover

A type of failover performed by the platform-specific cluster manager. If a node or the instance running on it fails, then the cluster manager restarts the instance on another node in the cluster. Restarting the Oracle instance requires moving the IP addresses, volumes, and file systems containing the Oracle datafiles. It also requires starting the Oracle server and opening the datafiles on the new node.


A periodic message that shows that an instance is active.

high availability

A type of system with redundant components that provides consistent and uninterrupted service, even when hardware or software fails. Availability is often expressed as a percentage of time that the database is available over the period of a year, such as 99.95%. It can also be expressed as the number of hours times the number of days in the week that the system is expected to run, such as 24 hours a day and 7 days a week. High availability can be defined to exclude unplanned downtime only or both planned and unplanned downtime.

home node

The default node for a specific pack. At initial startup, each pack runs on its home node. See also foreign node.

hub configuration

A configuration in which a single node serves as the secondary node to several primary nodes.


The combination of the System Global Area (SGA) and each process for the Oracle database. The memory and processes of an instance manage the associated database's data and serve the database users. Each instance has unique system identifier (SID), instance name, rollback segments, and thread ID.


The communication link between the nodes.

interprocess communication (IPC)

A high-speed operating system-dependent transport component. The IPC transfers messages between instances on different nodes. Also referred to as the interconnect.


See interprocess communication (IPC).


A process that resides on the server to listen for incoming client connection requests and manage the traffic to the server. When a client requests a network session with a server, a listener receives the request. If the client information matches the listener information, then the listener grants a connection to the server.


A listener configuration file that identifies the following for a listener:

The listener.ora file typically resides in $ORACLE_HOME/network/admin on UNIX platforms. Oracle9i does not require identification of the database service because of service registration. However, static service configuration is required for Oracle Enterprise Manager.

mean time between failures (MTBF)

The average time (usually expressed in hours) that a component works without failure. It is calculated by dividing the total number of failures into the total number of operating hours observed. The term can also mean the length of time a user can reasonably expect a device or system to work before an failure occurs.

mean time to failure (MTTF)

The average period of time that a component will work until failure.

mean time to recover (MTTR)

The average time that it takes to get a failed piece of hardware back online. Outside the context of Real Application Clusters, the acronym MTTR is also used for mean time to repair.


See mean time between failures (MTBF).


See mean time to failure (MTTF).


See mean time to recover (MTTR).


A node is a machine on which an instance resides.

Oracle Net

A software component that enables connectivity. It includes a core communication layer called the Oracle Net foundation layer and network protocol support. Oracle Net allows services and their applications to reside on different computers and communicate as peer applications. The main function of Oracle Net is to establish network sessions and transfer data between a client machine and a server or between two servers. After a network session has been established, Oracle Net acts as a data courier for the client and the server.

Oracle Real Application Clusters

A breakthrough architecture that allows clusters to access a shared database. Real Application Clusters includes the software component that provides the necessary Real Application Clusters scripts, initialization files, and datafiles to make the Oracle9i Enterprise Edition an Oracle9i Real Application Clusters database.

Oracle Real Application Clusters Guard

A failover protection feature. Oracle Real Application Clusters Guard is an integral component of Real Application Clusters. Oracle Real Application Clusters Guard provides the following functions:


Software that ensures the availability of the set of resources required to run an Oracle instance. The pack controls the startup, shutdown, and restarting of Oracle processes. There is one pack for each instance.

planned downtime

Includes routine operations, maintenance, and upgrades that cause the system to be unavailable to users. See also unplanned downtime.

preferred primary node

The node where the pack with the primary role resides by default at startup. See also preferred secondary node.

preferred secondary node

The node where the pack with the secondary role resides by default at startup. See also preferred primary node.

primary instance

In primary/secondary configurations, the instance through which all clients access the database. See also secondary instance.

primary instance role

In primary/secondary configurations, the instance that mounts the database first assumes the primary role. It performs the work requested by application sessions. If the primary instance fails or is shut down, then failover occurs, and another instance assumes the primary instance role. See also primary/secondary configuration and secondary instance role.

primary/secondary configuration

A configuration in which the primary instance is the instance where all clients access the database. The secondary instance provides backup services to the primary instance in case the primary instance fails. See also primary instance, primary instance role, secondary instance, and secondary instance role.

Real Application Clusters

See Oracle Real Application Clusters.

relocatable IP address

A public IP address that is configured to be up or down by the Oracle Real Application Clusters Guard pack.


A two-node cluster is resilient if both nodes have instances that are active. If the primary node has an instance that is active but the instance on the secondary node is down, the cluster is in a nonresilient state.

ring configuration

A configuration in which each node serves as a primary node and also as a secondary node for another node, forming a closed ring.


The ability to add additional nodes to Real Application Clusters environments and achieve markedly improved performance.

secondary instance

In a primary/secondary configuration, the instance that provides backup services to the primary instance in case the primary instance fails.

secondary instance role

In a primary/secondary configuration, the second instance to mount the database assumes the secondary role. The instance with the primary role performs the work that is requested by application sessions, but selected tasks such as reporting and planned operations can be performed by the instance with the secondary instance role. See also primary instance, primary instance role, and secondary instance.

service name

A logical representation of a database. This is the way a database is presented to clients. A database can be presented as multiple services and a service can be implemented as multiple database instances. The service name is a string that includes:

The service name is entered during installation or database creation.

If you are not sure what the global database name is, you can obtain it from the combined values of the SERVICE_NAMES parameter in the common database initialization file.

The service name is included in the CONNECT_DATA part of the connect descriptor.

service registration

A feature whereby PMON, the process monitor, automatically registers information with a listener. Because this information is registered with the listener, the listener.ora file does not need to be configured with this static information.

Service registration provides the listener with the following information:

System Global Area (SGA)

A group of shared memory structures that contain data and control information for one Oracle database instance. The SGA and Oracle processes constitute an Oracle instance. Oracle automatically allocates memory for an SGA whenever you start an instance and the operating system reclaims the memory when you shut down the instance. Each instance has only one SGA.


See Transparent Application Failover (TAF).


Occurs when the secondary node executes failover of the primary instance role to itself. Occurs only when the primary instance is unavailable and the primary instance role has not resumed normal function on a new node. See also primary instance, primary instance role, primary/secondary configuration, secondary instance, and secondary instance role.


See Transport Network Substrate (TNS).


A file that contains net service names. This file is needed on clients, nodes, the console, and the Oracle Performance Manager machine.


An action is transparent if it takes place without any effect that is visible to users.

Transparent Application Failover (TAF)

A runtime failover for high availability environments, such as Real Application Clusters and Oracle Real Application Clusters Guard. TAF refers to the failover and reestablishment of application-to-service connections. It allows client applications to automatically reconnect to the database if the connection fails, and optionally resume a SELECT statement that was in progress. This reconnect happens automatically from within the Oracle Call Interface (OCI) library.

Transport Network Substrate (TNS)

A foundation technology, built into the Oracle Net foundation layer that works with any standard network transport protocol.

unplanned downtime

System downtime that includes system faults, data and media errors, and site outages that cause the system to be unavailable to users. See also planned downtime.

warming the library cache

The process of transferring information about parsed SQL statements and compiled PL/SQL units from the library cache on the primary instance to the library cache on the secondary instance. Warming the cache improves performance after failover because the library cache is already populated.

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