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.

administrator-managed database

A database that you specifically define on which servers it can run, and where services can run within the database.

cache coherency

The synchronization of data in multiple caches so that reading a memory location through any cache will return 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 RAC that provides copies of blocks directly from a holding instance's memory cache to a requesting instance's memory cache.


The number of database instances you want running during normal operations.


A multitenant container database (CDB) is an Oracle database that includes zero, one, or many user-created pluggable databases (PDBs). Every Oracle database is either a CDB or a non-CDB.

client cluster

A cluster that advertises its names with the server cluster.


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

cluster configuration policy

A document that contains exactly one definition for each server pool defined in the system.

cluster configuration policy set

A document that defines the names of all server pools configured in the cluster and contains one or more configuration policies.

cluster database

The generic term for a Oracle RAC 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 Ready Services Daemon (CRSD)

The primary Oracle Clusterware process that performs high availability recovery and management operations, such as maintaining OCR. Also manages application resources and runs as root user (or by a user in the admin group on Mac OS X-based systems) and restarts automatically upon failure.

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. The Global Enqueue Service Monitor (LMON), a background process that monitors the health of the cluster database environment and registers and de-registers from CSS. See also, OCSSD.

Cluster Time Synchronization Service

A time synchronization mechanism that ensures that all internal clocks of all nodes in a cluster are synchronized.

Cluster Verification Utility (CVU)

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

commit outcome

A message sent to the client from the Oracle database after a transaction has been committed. These messages are not durable.

database pool

A set of databases within a database cloud that provide a unique set of global services and belong to a certain administrative domain. Partitioning of cloud databases into multiple pools simplifies service management and provides higher security because each pool can be administered by a different administrator.

Distributed Transaction Processing (DTP)

The paradigm of distributed transactions, including both XA-type externally coordinated transactions, and distributed-SQL-type (database links in Oracle) internally coordinated transactions.

dynamic network

A network that uses DHCP for IPv4 or stateless autoconfiguration (autoconfig) for IPv6.

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.

failure group

A failure group is a subset of the disks in a disk group, which could fail at the same time because they share hardware. Failure groups are used to store mirror copies of data.

Fast Application Notification (FAN)

Applications can 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 Database 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 Database gives the client a connection to an active instance that provides the requested database service.

file system

A file system is a software component providing structured access to disks. File systems present objects, such as files, to application programs. Access to files is generally specified with standard API defining operating system calls such as Open/Close and Read/Write that the application program uses for accessing files. File systems are usually provided as a component of an operating system, but may be provided as an independent software component.

forced disk write

In Oracle RAC, 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.

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)

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: OP.US.FOO.COM

global dynamic performance views (GV$)

Dynamic performance views storing information about all open instances in an Oracle RAC 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 Plug and Play Daemon (GPNPD)

This process provides access to the Grid Plug and Play profile, and coordinates updates to the profile among the nodes of the cluster to ensure that all of the nodes node have the most recent profile.

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).

high availability

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

Hub Node

A node in an Oracle Flex Cluster that is tightly connected with other servers and has direct access to shared storage.


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 Database allocates a memory area called the System Global Area (SGA) and starts one or more Oracle Database processes. This combination of the SGA and the Oracle Database processes is called an instance. Each instance has unique Oracle System Identifier (SID), instance name, rollback segments, and thread ID.

instance caging

A method that uses an initialization parameter to limit the number of CPUs that an instance can use simultaneously for foreground processes.

instance membership recovery

The method used by Oracle RAC guaranteeing that all cluster members are functional or active. instance membership recovery 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 is used to uniquely identify a specific instance when clusters share common services names. The instance name is identified by the INSTANCE_NAME parameter in the instance initialization file, initsid.ora. The instance name is the same as 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 will ensure that it does not use space allocated for other instances.


The communication link between nodes.


A container that stores a Transparent Data Encryption key. In previous releases, this was referred to as a wallet.

Leaf Node

Servers that are loosely coupled with Hub Nodes, which may not have direct access to the shared storage.

Logical Volume Manager (LVM)

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

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.

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 system. The MBR program then transfers control to the boot sector of the startup partition, which continues the startup process.

memory pressure

A state indicating that there is a limited amount of available memory on a server.


The rate of change in a cumulative statistic.

multitenant container database

See CDB.


Non-deterministic functions that can change their results each time they are called. Mutable functions can cause replay to be rejected, if the function results change at replay. Consider sequence.nextval and SYSDATE used in key values. If a primary key is built with values from these function calls, and is used in later foreign keys or other binds, then, at replay the same function result must be returned. Application Continuity provides mutable value replacement at replay for granted Oracle function calls to provide opaque bind-variable consistency.

Network Attached Storage (NAS)

Storage that is attached to a server by way of 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.

Network Interface Card (NIC)

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


A node is a computer system on which Oracle RAC and Oracle Clusterware software are 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.

Oracle Cluster File Systems

Oracle offers two cluster file systems, OCFS2 for Linux and Oracle ASM Cluster File System (Oracle ACFS). While Oracle ACFS is a proprietary file system, the source for OCFS2 for Linux is available to all under GNUs' General Public License (GPL). The two file systems are not compatible.

Oracle Cluster Registry (OCR)

The Oracle RAC configuration information repository that manages information about the cluster node list and instance-to-node mapping information. 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 Extended Cluster

A cluster consist of nodes that are located in multiple locations called sites.

Oracle Flex Cluster

Large clusters that are made of up of two types of nodes: Hub Nodes and Leaf Nodes, where the Hub Nodes form a cluster using current membership algorithms and Leaf Nodes connect for membership to a single Hub Node.

Oracle Grid Infrastructure

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

Oracle Grid Naming Service Daemon (GNSD)

The Oracle Grid Naming Service is a gateway between the cluster mDNS and external DNS servers. The gnsd process performs name resolution within the cluster.

Oracle High Availability Services Daemon (OHASD)

This process anchors the lower part of the Oracle Clusterware stack, which consists of processes that facilitate cluster operations.

Oracle Interface Configuration Tool (OIFCFG)

A command-line tool for both noncluster 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 also uses OIFCFG to identify and display available interfaces.

Oracle Managed Files

A service that automates naming, location, creation, and deletion of database files such as control files, redo log files, data files and others, based on a few initialization parameters. You can use Oracle Managed Files on top of a traditional file system supported by the host operating system, for example, VxFS or ODM. It can simplify many aspects of the database administration by eliminating the need to devise your own policies for such details.

Oracle Notification Service

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

Oracle Universal Installer

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

Oracle XA

An external interface that allows global transactions to be coordinated by a transaction manager other than Oracle Database.


In a multitenant container database (CDB), a portable collection of schemas, schema objects, and nonschema objects that appears to an Oracle Net client as a non-CDB.

pluggable database

See PDB.

policy-managed database

A database that you define as a cluster resource. Management of the database is defined by how you configure the resource, including on which servers the database can run and how many instances of the database are necessary to support the expected workload.

raw device

A disk drive that does not yet have a file system set up. Raw devices are used for Oracle RAC because they enable the sharing of disks. See also raw partition.

raw partition

A portion of a physical disk that is accessed at the lowest possible level. A raw partition is created when an extended partition is created and logical partitions are assigned to it without any formatting. Once formatting is complete, it is called a cooked partition. See also raw device.

recoverable error

A class of errors that arise due to an external system failure, independent of the application session logic that is executing. Recoverable errors occur following planned and unplanned outages of foregrounds, networks, nodes, storage, and databases. The application receives an error code that can leave the application not knowing the status of the last operation submitted.

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 run RMAN as a command line utility from the operating system (O/S) prompt or use the GUI-based Oracle Enterprise Manager Backup Manager.


A logical boundary that contains database clients and servers that are considered to be close to each other.


A unit of work submitted from the application. A request typically corresponds to the SQL and PL/SQL, and other database calls of a single web request, on a single database connection, and generally is demarcated by the calls made to check-out and check-in the database connection from a connection pool.

result cache

A result cache is an area of memory, either in the SGA or client application memory, that stores the result of a database query or query block for reuse. The cached rows are shared across statements and sessions unless they become stale.

Runtime Connection Load Balancing

Enables Oracle Database 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 runtime connection load balancing.


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

Secure Shell (SSH)

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

Server Control Utility (SRVCTL)

Server Management (SRVM) comprises the components required to operate Oracle Enterprise Manager in Oracle RAC. 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.


A computer system that has no Oracle software installed upon it.

server cluster

The cluster in which the shared GNS server is running.

server group

A logical partition of nodes in a cluster into a group that hosts applications, databases, or both. Server groups can be members of other server groups.

service level

A measure of the performance of a system.


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.

session state consistency

After a COMMIT has executed, if the state was changed in that transaction, then it is not possible to replay the transaction to reestablish that state if the session is lost. When configuring Application Continuity, the applications are categorized depending on whether the session state after the initial setup is dynamic or static, and then whether it is correct to continue past a COMMIT operation within a request.

  • Dynamic: (default) A session has dynamic state if the session state changes are not fully encapsulated by the initialization, and cannot be fully captured in a callback at failover. Once the first transaction in a request commits, failover is internally disabled until the next request begins. This is the default mode that most applications should use for requests.

  • Static: (special—on request) A session has a static state if all session state changes, such as NLS settings and PL/SQL package state, can be repeated in an initialization callback. This setting is used only for database diagnostic applications that do not change session state inside requests. Do not set STATIC mode if there are any non-transactional state changes in the request that cannot be reestablished by a callback. If you are unsure, use DYNAMIC mode.

shared everything

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

single client access name (SCAN)

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.

singleton services

Services that run on only one instance at any one time. By defining the Distributed Transaction Property (DTP) property of a service, you can force the service to be a singleton service.

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.

SQL translation profile

A SQL translation profile is a database schema object that directs how SQL statements in non-Oracle databases are translated to Oracle, and how Oracle error codes and ANSI SQLSTATES are translated into other vendors' equivalents.

system identifier (SID)

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

transparent application failover (TAF)

A runtime failover for high-availability environments, such as Oracle RAC and Oracle RAC Guard, 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 library.

Virtual Internet Protocol (VIP)

An IP address assigned to multiple applications residing on a single server, multiple domain names, or multiple servers, rather than being assigned to a specific single server or network interface card (NIC).

volume manager

A volume manager is a software component that manages the mapping of the collection of the pieces of the disks into a volume.

voting disk

A file that manages information about node membership.