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.
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.
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.
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.
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.
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.
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 OS X-based systems) and restarts automatically upon failure.
The paradigm of distributed transactions, including both XA-type externally coordinated transactions, and distributed-SQL-type (database links in Oracle) internally coordinated transactions.
A graphical user interface-based configuration assistant that you can use to configure Oracle Enterprise Manager features.
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.
A Linux or UNIX event manager daemon that starts the
racgevt process to manage callouts.
A cluster where the nodes in the cluster are separated by greater distances from two buildings across the street, to across a campus or across a city. For availability reasons, the data needs to be located at both sites, and therefore one needs to look at alternatives for mirroring the storage.
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 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
DOWN events. In response, Oracle Database gives the client a connection to an active instance that provides the requested database service.
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.
In 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.
Process that implement 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).
Processes that manage remote messages. Oracle RAC provides for up to 10 Global Cache Service Processes.
Global resources that coordinate access to data blocks in the buffer caches of multiple Oracle RAC instances to provide cache coherency.
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.ORACLE.COM
Dynamic performance views storing information about all open instances in a Real Application Clusters cluster. (Not only the local instance.) In contrast, standard dynamic performance views (
V$) only store information about the local instance.
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.
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.
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 by default.
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).
The Oracle Hardware Assisted Resilient Data (HARD) Initiative prevents data corruptions. The HARD initiative uses Oracle data validation algorithms inside storage devices to prevent writing corrupted data to permanent storage.
Systems with redundant components that provide consistent and uninterrupted service, even in the event of hardware or software failures. This involves some degree of redundancy.
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.
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.
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).
A number that associates extents of data blocks with particular instances. The instance number enables you to start up 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.
A generic term that describes Linux or UNIX subsystems for online disk storage management.
A high-speed operating system-dependent transport component. The IPC transfers messages between instances on different nodes. Also referred to as the interconnect.
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.
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 card that you insert into a computer to connect the computer to a network.
Oracle offers two cluster file systems, OCFS for Windows and OCFS2 for Linux. While OCFS for Windows 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.
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.
The Oracle interface that maps symbolic links to logical drives and displays them in the OLM graphical user interface.
A process that runs on nodes in Oracle RAC environments.
OCLSOMON monitors CSS hangs that result from load or scheduling issues. If
OCLSOMON detects either of these, the process shuts down the affected node to prevent database corruption.
OCLSVMON is a process that runs when vendor clusterware is installed. Basically due to the existence of this process, the Oracle Clusterware can delay log flushes. This delay is useful in diagnosing problems because the vendor clusterware allows a delay of eviction processing until after log files have flushed.
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.
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 also uses OIFCFG to identify and display available interfaces.
A publish and subscribe service for communicating information about all FAN events.
A Linux or UNIX process monitor for a cluster. Note that this process will only appear on platforms that do not use vendor clusterware with 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.
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).
A disk drive that does not yet have a file system set up. Raw devices are used for Oracle Real Application Clusters because they enable the sharing of disks. See also 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.
An Oracle tool that enables you to back up, copy, restore, and recover datafiles, 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 Oracle Enterprise Manager Backup Manager.
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 Real Application Clusters applications and achieve markedly improved scale-up and speed-up.
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 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.
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.
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.
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.
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.
A runtime failover for high-availability environments, such as Oracle Real Application Clusters and Oracle Real Application Clusters 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.