administrator-managed database

An administrator-managed database is a database created on nodes that are not part of a server pool; the database or clusterware administrator manages these databases.


Any strategy that is expected to increase the probability that an application or client finds the requested data cached in the instance to which the request is routed.

affinity hint

A flag that indicates if affinity is active or inactive for a particular instance and service combination.

all node patching

A method of applying patches to the nodes in a cluster. When using the all node patching method, all the nodes that are part of the Oracle Real Application Clusters database are initially brought down and the patch is applied on all the nodes. After the patch is applied to all nodes, then the nodes are brought back up.

Application Continuity

A feature that can reestablish database sessions and resubmit pending work for recoverable errors, thereby protecting applications from transient failures. When a component fails, the recovery restores the state as it was before the failure. A user request is executed on time and at most once.

Automatic Workload Repository (AWR)

A built-in repository that exists in every Oracle Database. At regular intervals, Oracle Database makes a snapshot of all of its vital statistics and workload information and stores them in the AWR.

cache coherency

The synchronization of data in multiple caches so that reading a memory location through any cache returns the most recent data written to that location through any other cache. Sometimes called cache consistency.

Cache Fusion

A diskless cache coherency mechanism in Oracle Real Application Clusters that provides copies of blocks directly from a holding instance's memory cache to a requesting instance's memory cache.


Multiple interconnected computers or servers that appear as if they are one server to end users and applications.

cluster database

The generic term for an Oracle Real Application Clusters database.

cluster file system

A distributed file system that is a cluster of servers that collaborate to provide high performance service to their clients. Cluster file system software deals with distributing requests to storage cluster components.

Cluster Synchronization Services (CSS)

An Oracle Clusterware component that discovers and tracks the membership state of each node by providing a common view of membership across the cluster. CSS also monitors process health, specifically the health of the database instance. See also OCSSD.

Cluster Verification Utility (CVU)

A tool that verifies a wide range of Oracle RAC-specific components such as shared storage devices, networking configurations, system requirements, Oracle Clusterware, groups, and users.

connect descriptor

A specially formatted description of the destination for a network connection. A connect descriptor contains destination service and network route information. The network route provides, at a minimum, the location of the listener through use of a network address.


A Linux or UNIX process that performs high availability recovery and management operations such as maintaining the OCR. Also manages application resources and runs as root user (or by a user in the admin group on Mac operating system X-based systems) and restarts automatically upon failure.

database services

Entities that you can define in Oracle RAC databases that enable you to group database workloads and route work to the optimal instances that are assigned to offer the service.

Dynamic Host Configuration Protocol (DHCP)

A network application protocol used by devices (DHCP clients) to obtain configuration information for operation in an Internet Protocol network. This protocol reduces system administration workload, enabling devices to be added to the network with little or no manual intervention.

Event Manager (EVM)

The background process that publishes Oracle Clusterware events. EVM scans the designated callout directory and runs all scripts in that directory when an event occurs.

Event Manager Daemon (EVMD)

A Linux or UNIX event manager daemon that starts the racgevt process to manage callouts.

Fast Application Notification (FAN)

Applications use FAN to enable rapid failure detection, balancing of connection pools after failures, and re-balancing of connection pools when failed components are repaired. The FAN notification process uses system events that Oracle publishes when cluster servers become unreachable or if network interfaces fail.

Fast Connection Failover

Fast Connection Failover provides high availability to FAN integrated clients, such as clients that use JDBC, OCI, or ODP.NET. If you configure the client to use fast connection failover, then the client automatically subscribes to FAN events and can react to database UP and DOWN events. In response, Oracle gives the client a connection to an active instance that provides the requested database service.

forced disk write

In Oracle Real Application Clusters, a particular data block can only be modified by one instance at a time. If one instance modifies a data block that another instance needs, then whether a forced disk write is required depends on the type of request submitted for the block.

Free pool

A default server pool used in policy-based cluster and capacity management of Oracle Clusterware resources. The free pool contains servers that are not assigned to any server pool.

General Parallel File System (GPFS)

General Parallel File System (GPFS) is a shared-disk IBM file system product that provides data access from all of the nodes in a homogenous or heterogeneous cluster.

Global Cache Service (GCS)

A process that implements Cache Fusion. It maintains the block mode for blocks in the global role. It is responsible for block transfers between instances. The Global Cache Service employs various background processes such as the Global Cache Service Processes (LMSn) and Global Enqueue Service Daemon (LMD).

Global Cache Service Processes (LMSn)

Processes that manage remote messages. Oracle RAC provides for up to 10 Global Cache Service Processes.

Global Cache Service (GCS) resources

Global resources that coordinate access to data blocks in the buffer caches of multiple Oracle RAC instances to provide cache coherency.

global database name

The full name of the database that uniquely identifies it from any other database. The global database name is of the form database_name.database_domain—for example: TEST.US.EXAMPLE.COM

global dynamic performance views

Dynamic performance views storing information about all open instances in an Oracle Real Application Clusters cluster. (Not only the local instance.) In contrast, standard dynamic performance views (V$) only store information about the local instance.

Global Enqueue Service (GES)

A service that coordinates enqueues that are shared globally.

Global Enqueue Service Daemon (LMD)

The resource agent process that manages requests for resources to control access to blocks. The LMD process also handles deadlock detection and remote resource requests. Remote resource requests are requests originating from another instance.

Global Enqueue Service Monitor (LMON)

The background LMON process monitors the entire cluster to manage global resources. LMON manages instance deaths and the associated recovery for any failed instance. In particular, LMON handles the part of recovery associated with global resources. LMON-provided services are also known as Cluster Group Services.

Global Services Daemon (GSD)

A component that receives requests from SRVCTL to execute administrative job tasks, such as startup or shutdown. The command is executed locally on each node, and the results are returned to SRVCTL. GSD is installed on the nodes by default.

Grid home

The Oracle Home directory for Oracle Grid Infrastructure for a cluster, which includes Oracle Clusterware and Oracle ASM.

grid infrastructure

The software that provides the infrastructure for an enterprise grid architecture. Oracle Grid Infrastructure for a cluster bundles these infrastructure software products into one product. In an Oracle cluster, Oracle Grid Infrastructure for a cluster includes Oracle Clusterware and Oracle Automatic Storage Management (Oracle ASM). For a standalone Oracle Database server, Oracle Grid Infrastructure for a cluster includes Oracle Restart and Oracle ASM.

Grid Naming Service (GNS)

A generic service which resolves the names of hosts in a delegated normal DNS zone by mapping them to IP addresses within the zone. GNS enables the use of Dynamic Host Configuration Protocol (DHCP) address for Oracle RAC database nodes, simplifying deployment. GNS also resolves host names passed back from a SCAN listener.

high availability

Systems with redundant components that provide consistent and uninterrupted service, even following hardware or software failures. This involves some degree of redundancy.

High Availability Cluster Multi-Processing (HACMP)

High Availability Cluster Multi-Processing is an IBM AIX-based high availability cluster software product. HACMP has two major components: high availability (HA) and cluster multi-processing (CMP).


For an Oracle RAC database, each node in a cluster usually has one instance of the running Oracle software that references the database. When a database is started, Oracle allocates a memory area called the System Global Area (SGA) and starts one or more Oracle processes. This combination of the SGA and the Oracle processes is called an instance. Each instance has unique Oracle System Identifier (SID), instance name, rollback segments, and thread ID.

instance membership recovery

The method used by Oracle RAC guaranteeing that all cluster members are functional or active. IMR polls and arbitrates the membership. Any members that do not show a heartbeat by way of the control file or who do not respond to periodic activity inquiry messages are presumed terminated.

instance name

Represents the name of the instance and uniquely identifies a specific instance when clusters share common services names. The INSTANCE_NAME parameter in the instance initialization file, initsid.ora, identifies the instance name. The instance name equals the Oracle System Identifier (SID).

instance number

A number that associates extents of data blocks with particular instances. The instance number enables you to start an instance and ensure that it uses the extents allocated to it for inserts and updates. This ensures that an instance does not use space allocated for other instances.


The private network communication link used to synchronize the memory cache of the nodes in the cluster.


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

logical transaction ID

A globally unique identifier that defines a transaction from the application perspective.

Logical Volume Manager (LVM)

A generic term that describes Linux or UNIX subsystems for online disk storage management.

Inter-Process 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.

Master Boot Record (MBR)

A program that executes when a computer starts. Typically, the MBR resides on the first sector of a local hard disk. The program begins the startup process by examining the partition table to determine which partition to use for starting the computer. The MBR program then transfers control to the boot sector of the startup partition, which continues the startup process.

minimum downtime patching

In minimum downtime patching, the nodes are divided into two sets. The first set is shut down and the patch is applied to it. The second set is then shut down. The first set is brought up and then the patch is applied to the second set. After the patch is applied to the second set, those nodes are also brought up, finishing the patching operation.

multicast Domain Name Server (mDNS)

A part of Zero Configuration Networking (Zeroconf), mDNS provides the ability to address hosts using DNS-like names without the need of an existing, managed DNS server.


Data returned from mutable objects. An example of a mutable is a call to SYSTIMESTAMP function.

mutable objects

A function that obtains a new value every time it is called. Examples of mutable objects are SYSDATE, SYSTIMESTAMP, SYS_GUID, and sequence.NEXTVAL.

net service name

A simple name for a service that resolves to a connect descriptor. Users initiate a connect request by passing a user name and password along with a net service name in a connect string for the database service to which they want to connect.

Network Attached Storage (NAS)

Storage that is attached to a server by way of a network.

Network Interface Card (NIC)

A card that you insert into a computer to connect the computer to a network.

network switch

A hardware device that connects computers within a network.

Network Time Protocol (NTP)

An Internet standard protocol, built on top of TCP/IP, that ensures the accurate synchronization to the millisecond of the computer clock times in a network of computers.


A node is a computer on which the Oracle Clusterware software is installed or will be installed.

Object Link Manager (OLM)

The Oracle interface that maps symbolic links to logical drives and displays them in the OLM graphical user interface.


A Linux or UNIX process that manages the Cluster Synchronization Services (CSS) daemon. Manages cluster node membership and runs as oracle user; failure of this process results in cluster restart.

optimal flexible architecture (OFA)

A set of file naming and configuration guidelines created to ensure reliable Oracle installations that require little maintenance.

Oracle Base directory

The mountpoint for all software installations performed by a particular user. An Oracle base directory can contain multiple Oracle homes for Oracle software products, either of the same or different releases, all installed by the same operating system user. The Oracle Base directory is also the directory where the software parameter files, log files, trace files, and so on, associated with a specific installation owner are located.

Oracle Cluster File System (OCFS)

The Oracle proprietary cluster file system software that is available for Linux platforms.

Oracle Cluster Registry (OCR)

The Oracle RAC configuration information repository that manages information about the cluster node list and instance-to-node mapping information. The OCR also manages information about Oracle Clusterware resource profiles for customized applications.

Oracle Clusterware

This is clusterware that is provided by Oracle to manage cluster database processing including node membership, group services, global resource management, and high availability functions.

Oracle Home directory

The binary location for a particular software installation.

Typically The Oracle Home directory is a subdirectory of the Oracle Base directory for the software installation owner. However, with Oracle Grid Infrastructure for a cluster, the Oracle Home directory (in this case, the Grid home) is located outside of the Oracle Base directory for the Oracle Grid Infrastructure for a cluster installation owner, because the path of the Grid home is changed to root ownership.

Oracle Interface Configuration Tool (OIFCFG)

A command-line tool for both single-instance Oracle databases and Oracle RAC databases that enables you to allocate and de-allocate network interfaces to components, direct components to use specific network interfaces, and retrieve component configuration information. The Oracle Universal Installer (OUI) also uses OIFCFG to identify and display available interfaces.

Oracle Inventory directory

The Oracle Inventory directory is the central inventory location for all Oracle software installed on a server.

Oracle Notification Services (ONS)

A publish and subscribe service for communicating information about all FAN events.

Oracle Universal Installer (OUI)

A tool to install Oracle Clusterware, the Oracle relational database software, and the Oracle Real Application Clusters software. You can also use the Oracle Universal Installer to launch the Database Configuration Assistant (DBCA).

policy-managed database

A policy-managed database is created using a server pool. Oracle Clusterware allocates and reassigns capacity based on policies you define, enabling faster resource failover and dynamic capacity assignment.

recoverable error

A class of errors that arise because of an external system failure, independently of the application session logic that is executing. Recoverable errors occur following planned and unplanned outages of networks, nodes, storage, and databases. An example of a nonrecoverable error is submission of invalid data values.

Recovery Manager (RMAN)

An Oracle tool that enables you to back up, copy, restore, and recover data files, control files, and archived redo logs. It is included with the Oracle server and does not require separate installation. You can invoke RMAN as a command line utility from the operating system (O/S) prompt or use the GUI-based Enterprise Manager Backup Manager.

redo thread

The redo generated by a database instance.


A sequence of operations on a database connection that uses client and server non-transactional states. A request may include zero or more database transactions. Global transactions can span requests.

request boundary

The beginning or end of a request. A request begins when a connection is borrowed from the Universal Connection Pool (UCP) or WebLogic Server connection pool, and ends when this connection is returned to the connection pool. A request boundary can also be explicitly defined with application calls such as beginRequest and endRequest. See also request.

rolling patching

In Rolling Patching, one node (or group of nodes) is shutdown, the patch applied and the node brought back up again. This is repeated for each node in the cluster until all the nodes in the Real Application Clusters are patched.

Run-time Connection Load Balancing

Enables Oracle to make intelligent service connection decisions based on the connection pool that provides the optimal service for the requested application based on current workloads. The JDBC, ODP.NET, and OCI clients are integrated with the load balancing advisory; you can use any of these client environments to provide run-time connection load balancing.


The ability to add additional nodes to Oracle Real Application Clusters applications and achieve markedly improved scale-up and speed-up.


A single name, or network alias, for the cluster. Oracle Database 11g database clients use SCAN to connect to the database. SCAN can resolve to multiple IP addresses, reflecting multiple listeners in the cluster handling public client connections.

Secure Shell (SSH)

A program for logging into a remote computer over a network. You can use SSH to execute commands on a remote computer and to move files from one computer to another. SSH uses strong authentication and secure communications over insecure channels.

Server Control (SRVCTL) Utility

Server Management (SRVM) comprises the components required to operate Oracle Enterprise Manager in Oracle Real Application Clusters. The SRVM components, such as the Intelligent Agent, Global Services Daemon, and SRVCTL, enable you to manage cluster databases running in heterogeneous environments through an open client/server architecture using Oracle Enterprise Manager.

server pool

A server pool is a logical division of nodes in a cluster into a group to support policy-managed databases.

shared everything

A database architecture in which all instances share access to all of the data.

singleton services

Services that run on only one instance at any one time.

split brain syndrome

Where two or more instances attempt to control a cluster database. In a two-node environment, for example, one instance attempts to manage updates simultaneously while the other instance attempts to manage updates.

system identifier (SID)

The Oracle system identifier (SID) identifies a specific instance of the running Oracle software. For an Oracle Real Application Clusters database, each node within the cluster has an instance referencing the database.


Each Oracle instance has its own set of online redo log groups. These groups are called a thread of online redo. In non-Oracle Real Application Clusters environments, each database has only one thread that belongs to the instance accessing it. In Oracle Real Application Clusters environments, each instance has a separate thread, that is, each instance has its own online redo log. Each thread has its own current log member.

thread number

An identifier for the redo thread to be used by an instance, specified by the INSTANCE_NUMBER initialization parameter. You can use any available redo thread number but an instance cannot use the same redo thread number as another instance.


A logical unit of work that contains one or more SQL statements. All statements in a transaction commit or roll back together. The use of transactions is one of the most important ways that a database management system differs from a file system.

transaction ID

An identifier that is unique to a transaction and represents the undo segment number, slot, and sequence number.

transaction idempotence

The ability to return a guaranteed outcome for a transaction: whether it committed and whether the call was completed.

transparent application failover (TAF)

A run-time failover for high-availability environments, such as Oracle Real Application Clusters, TAF refers to the failover and re-establishment of application-to-service connections. It enables 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.

voting disk

A file that manages information about node membership.