|Oracle9i Real Application Clusters Concepts
Release 1 (9.0.1)
Part Number A89867-02
In the client/server model, the part of the system that performs information preparation and exchange on behalf of a client or server. Especially in the phrase intelligent agent it implies an automatic process that can communicate with other agents to perform some collective tasks on behalf of one or more users.
See archive (ARCH)
The archive background process creates a single file containing one or (usually) more separate files plus information to allow them to be extracted (separated) by Real Application Clusters.
A blocking interrupt is a software synchronization feature that notifies the process holding the access right to a resource that another process needs to access the same resource in an incompatible mode. (The shared (S) mode and exclusive (X) mode, for example, are incompatible). See also acquisition interrupt.
The buffer state is the state of a buffer in the local cache of an instance.
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 also called cache consistency.
A diskless cache coherency mechanism, used in Real Application Clusters, that provides copies of blocks directly from the holding instance's memory cache to the requesting instance's memory cache. Cache Fusion is the collective term for the group of features that were phased in starting with Oracle8i.
A call is to operate a command in order to execute software functionality.
A cluster is a highly available combination of hardware and software. In a cluster, instances typically run on different nodes that coordinate with one another when accessing the shared database residing on disk.
A cluster database is the generic term for a database configured and controlled by the Real Application Clusters product.
The software layer that provides mechanisms for instances to exchange configuration information, interprocess communication (IPC) port identifiers, and other kinds of meta data needed for Real Application Clusters operation. Cluster group services are also known as LMON-provided services.
Cluster Manager is an Operating System-Dependent component that discovers and tracks the membership state of nodes by providing a common view of cluster membership across the cluster. CM monitors process health. The LMON process, a background process that monitors the health of the Global Cache Service (GCS), registers and de-registers from the CM. The CM also manages recovery from any network card or cable failures.
The Global Cache Service (GCS) ensures that a consistent read block (also known as the master copy data block) is maintained. The consistent read block is the master block version that holds all the changes. It is held in at least one System Global Area (SGA) in the cluster if the block is to be changed. If an instance needs to read it, then the current version of the block may reside in many buffer caches as a shared resource. Thus, the most recent copy of the block in all System Global Areas contains all changes made to that block by all instances, regardless of whether any transactions on those instances have committed.
Competition for resources. The term is used in networks to describe a situation where two or more nodes attempt to access the same resource at the same time. Contention is resolved by concurrency control mechanisms.
A cooked partition is a portion of a physical disk where an extended partition is created, logical partitions are assigned, and formatting has been completed. In contrast, a unformatted partitions is called a raw partition.
The part of a computer that controls all the other parts. A parallel computer has several CPUs that can share other resources such as memory and peripheral devices.
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
Abbreviation for disk and execution monitor. A program that is not invoked explicitly, but lies dormant waiting for specific conditions to occur.
An individual responsible for the design and management of the database and for the evaluation, selection and implementation of the database management system. In smaller organizations, the data administrator and database administrator are often the same individual. However, when they are different, the database administrator's function is more technical. The database administrator would implement the database software that meets the requirements outlined by the organization's data administrator and systems analysts. DBA is also an acronym for data block address.
A tool for creating and deleting databases.
The Database Mount Lock shows whether an instance has mounted a particular database in exclusive or shared mode. This lock is only used with Real Application Clusters. The Database Mount Lock is the only multi-instance lock used with Real Application Clusters in exclusive mode. It prevents another instance from mounting the database in shared or exclusive modes.
The database writer (DBWR) is a background process daemon that writes new data (modified blocks) from the System Global Area (SGA) to the datafiles. Each instance has a DBWR. The DBWR is optimized to minimize disk writes. Generally disk writes occur only when more data needs to be read into the SGA and there is not enough free space in the database buffers. The least recently used data is written to the datafiles first.
A language enabling the structure and instances of a database to be defined in a human-readable, and machine-readable form.
The structured query language (SQL) contains DDL commands that can be used either interactively or within programming language source code to define databases and their components, such as the
See dictionary cache
A datafile is a physical operating system file on disk that was created by Oracle. It contains data structures such as tables and indexes. A datafile can only belong to one database.
Software tools that help with decision support.
The data dictionary cache contains information from the data dictionary, the metadata store.
A data block that has been changed.
Dynamic resource remastering is the ability to move the ownership of a resource between instances of Real Application Clusters. Dynamic resource remastering is used to implement resource affinity for increased performance. Resource remastering is deferred when instances enter or leave the cluster.
Enqueues are shared memory structures that serialize access to database resources. Enqueues are local to one instance if Real Application Clusters is not enabled. When you enable Real Application Clusters, enqueues can be global to a database. (See also: latch, lock, and resource.)
A tool for creating, deleting, and modifying Enterprise Manager configurations and settings.
The buffer state name for an exclusive resource.
An extent is a specific number of contiguous data blocks, obtained in a single allocation, used to store a specific type of information.
The process used to assign a number of contiguous data blocks.
The means of failure recognition and recovery used by Real Application Clusters.
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.
A standard of the American National Standards Institute (ANSI) for a 100 Mb per second local area network architecture. The underlying medium is often optical fiber and the topology is a dual-attached, counter-rotating token ring.
Fibre Channel is the generic term for a high speed serial data transfer architecture recently standardized by the American National Standards Institute (ANSI). The Fibre Channel architecture was developed by the Fibre Channel Industry Association (FCIA), a consortium of computer and mass storage manufacturers. The best-known Fibre Channel standard is the Fibre Channel Arbitrated Loop (FC-AL). (See also: Storage Area Network (SAN).
A colloquial term for 99.999% system availability.
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. If the requesting instance needs the block for modification, then the holding instance's resources on the data block must be converted accordingly. The first instance must write the block to disk before the requesting instance can read it. This constitutes the forced disk write to a block. A forced disk write is also often called a ping. Most forced disk writes have been eliminated by Cache Fusion, because it provides copies of blocks directly from the holding instance's memory cache to the requesting instance's memory cache.
The node where a runs when it its not running on its default (home node). When a pack is running on its foreign (secondary) node, only the IP address is enabled.
A free list group is a set of free lists available for use by one or more instances.
A global cache element is an Oracle-specific data structure representing a Cache Fusion resource. There is a 1:1 corresponding relationship between a global cache element and a Cache Fusion resource in the Global Cache Service (GCS).
The Global Cache Service is the controlling 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).
The Global Cache Service Processes (LMSn) are the processes that handle remote Global Cache Service (GCS) messages. Current Real Application Clusters software provides for up to 10 Global Cache Service Processes. The number of LMSn varies depending on the amount of messaging traffic among nodes in the cluster. The LMSn handle the acquisition interrupt and blocking interrupt requests from the remote instances for Global Cache Service resources. For cross-instance consistent read requests, the LMSn will create a consistent read version of the block and send it to the requesting instance. The LMSn also control the flow of messages to remote instances.
This service coordinates enqueues that are shared globally.
The Global Enqueue Service Daemon (LMD) is the resource agent process that manages Global Enqueue Service (GES) resource requests. The LMD process also handles deadlock detection Global Enqueue Service (GES) requests. Remote resource requests are requests originating from another instance. (See also: daemon.)
The background Global Enqueue Service Monitor (LMON) monitors the entire cluster to manage global resources. LMON manages instance and process expirations and the associated recovery for the Global Cache Service (GCS) and Global Enqueue Service (GES). In particular, LMON handles the part of recovery associated with global resources. LMON-provided services are also known as cluster group services (CGS).
The data structures associated with global resources. It is distributed across all instances in a cluster.
The Global Services Daemon (GSD) is 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 sent back to SRVCTL. The daemon is installed on the nodes by default. It should not be deleted.
Hardware failover refers to failover performed by the platform-specific Cluster Manager (CM). If a node or the instance running on it fails, 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.
High availability refers to 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. 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.
The high water mark is the boundary between used and unused space in a segment.
A configuration in which a single node serves as the secondary node to several primary nodes.
INDX is the default database tablespace that stores indexes associated with the data in the
initsid.ora file is an initialization file that contains parameters unique for an instance and points to
.ora for database parameters.
.ora file is an initialization file that contains database parameters.
For a Real Application Clusters database, each node within the cluster has an instance of the running Oracle software referencing the database.
When a database is started on a database server (regardless of the type of system), 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 process is called an instance. The memory and processes of an instance manage the associated database's data efficiently and serve the one or more users of the database. You can connect to any instance to access any information that resides within a Real Application Clusters database.
Instance membership recovery (IMR) is the method used by Real Application Clusters guaranteeing that all cluster members are functional or active. IMR polls and arbitrates the membership. Any members that do not show a heartbeat in the control file record or who do not respond to periodic status queries are presumed to have expired. The Instance Membership Recovery arbiter settles the membership votes of nodes in a cluster, and creates a control file voting results record (CFVRR).
The instance name represents the name of the instance and is used to uniquely identify a specific instance when multiple instances share common services names. The instance name is identified by the
INSTANCE_NAME parameter in the initsid.ora file.
The instance name is the same as the system identifier (SID).
You can use various structured query language (SQL) options with the
INSTANCE_NUMBER initialization parameter to associate extents of data blocks with instances.
The instance number is depicted by the
INSTANCE_NUMBER parameter in the instance initialization file,
The communication link between the nodes.
Interprocess communication (IPC) is a high speed Operating System-Dependent transport component. IPC reliably transfers messages between instances on different nodes.
In the context of Real Application Clusters, I/O is an Operating System-Dependent component that provides I/O to access shared disks.
In the context of databases: The set of foreground and background processes that implement a database.
In the context of languages: An essential subset of a programming language, where other constructs are (or could be) defined. Also known as a core language.
In the context of operating systems: The essential part of Unix or other operating systems, responsible for resource allocation, low-level hardware interfaces, security, and so on.
A latch is a simple, low-level serialization mechanism that protect in-memory data structures in the System Global Area (SGA). Latches do not protect datafiles, are automatic, and are held for a very short time in exclusive mode. Because latches are synchronized within a node, they do not facilitate internode synchronization. (See also: enqueue, lock, and resource.)
The LCK process manages instance global enqueue requests and cross-instance call operations. Workload is automatically shared and balanced when there are multiple Global Cache Service Processes (LMSn).
Objects in the library cache can become invalid due to object dependencies. The object is recompiled on its next use.
The listener is a separate process that resides on the server whose responsibility is to listen for incoming client connection requests and manage the traffic to the server.
The listener brokers the client request, handing off the request to the server. Every time a client (or server acting as a client) requests a network session with a server, a listener receives the actual request. If the client's information matches the listener's information, then the listener grants a connection to the server.
A configuration file for the listener that identifies the listener name, protocol addresses that it is accepting connection requests on, and Services it is listening for.
listener.ora file typically resides in the
$ORACLE_HOME/network/admin directory on UNIX platforms and the
ORACLE_HOME\network\admin directory on Windows NT.
Oracle databases do not require identification of the database service in listener.ora because of service registration. However, static service configuration is required for an Oracle databases if you plan to use a listener.
Synchronization mechanisms utilized to coordinate concurrent access to shared data structures in cluster databases. Local enqueues are called local locks in single instance Oracle. (See also: enqueue.)
Computing that uses many separate CPUs running in parallel to execute a single program.
A list of blocks containing available space drawn from any extent in a table.
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.
The average period of time that a component will work until failure.
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.
The storage component used for programmatic execution and the buffering of data.
See shared server
See null (N) mode
Obsolete term. See Oracle Net
A node is a machine where an instance resides.
A memory architecture used in multiprocessors where the access time depends on the memory location. A processor can access its local memory faster than non-local memory. (Memory that is local to another processor or shared between processors.) (See also: uniform memory access (UMA))
This term is used interchangeably with Relational Database Management System (RDBMS).
The processing of transactions by computers in real time. (See also: transaction systems.)
The low-level software that handles the interface to peripheral hardware, schedules tasks, allocates storage, and presents a default interface to the user when no application program is running.
The Operating System can be split into a kernel that is always present and various system programs that use facilities provided by the kernel to perform higher-level house-keeping tasks, often acting as servers in a client/server relationship.
Operating System-Dependent (OSD) layers are software layers tailored for various operating systems. OSD clusterware provides communication links between the Operating System and Real Application Clusters software.
Obsolete acronym. See Oracle Real Application Clusters Guard
Obsolete program. See SRVCTL
An Application Programming Interface (API) that allows applications written in C or C++ to interact with one or more Oracle servers.
A system management tool that provides an integrated solution for centrally managing your heterogeneous environment. Oracle Enterprise Manager combines a graphical console, management server, Oracle Intelligent Agent, repository database, and tools to provide an integrated, comprehensive systems management platform for managing Oracle products.
A product family consists of system management tools designed to efficiently manage the complete Oracle environment.
Oracle Net is a software component that enables connectivity. It includes a core communication layer called the Oracle Net foundation layer and network protocol support. Oracle Net is the foundation of Oracle's family of networking products, allowing 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. Once a network session is established, Oracle Net acts as a data courier for the client and the server. Oracle Net was formerly called Net8. (See also: Oracle Net Services and Oracle Net Configuration Assistant.)
A post-installation tool that configures basic network components after installation, including:
Oracle Net Services is the term that encompasses all of the Oracle networking components, including: Oracle Net, the listener, Oracle Connection Manager, Oracle Names, Oracle Net Configuration Assistant, and Oracle Net Manager.
Obsolete product. See Oracle Real Application Clusters
An query coordinating option that enables you to make structured query language (SQL) statements parallel so that they can run on different processors in a parallel environments. When a instance is started, the Oracle database server creates a pool of query server processes. This pool is available for Oracle Parallel Query. Typically, Oracle Parallel Query is used for full table scans, sorts, subqueries, data loading, and so forth to improve performance. It is commonly used in Decision Support System (DSS) and data warehousing applications. (See also: Oracle parallel execution.)
An add-on application for Oracle Enterprise Manager that offers a variety of tabular and graphic performance statistics for Real Application Clusters. The statistics represent the aggregate performance for all instances running on Real Application Clusters.
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:
A pack is a piece or suite of 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. In the context of Real Application Clusters and Oracle Real Application Clusters Guard, Packs were formerly called PFS packs.
A file used by an Oracle server that provides specific values and configuration settings that are used at database startup. The keyword
PFILE is used in the startup command.
A file created by the
ORAPWD command. A database must use password files if you want to connect as
SYSDBA over a network.
A past image is a copy of dirty block that is used by the Global Cache Service (GCS). Past images of blocks are maintained until writes covering those versions are recorded. Past images are used in failure recovery.
A storage parameter file that defines the percentage of space to leave in an extent.
Obsolete term. See pack.
See past image (PI)
A synonymous term for a forced disk write.
Includes routine operations, maintenance, and upgrades that cause the system to be unavailable to users. (See also: unplanned downtime.)
PL/SQL is Oracle's procedural extension to the structured query language (SQL). SQL is the industry-standard database access language. An advanced 4GL (fourth-generation programming language), PL/SQL offers seamless SQL access, tight integration with the Oracle server and tools, portability, security, and modern software engineering features such as data encapsulation, overloading, exception handling, and information hiding.
In a primary/secondary configuration, 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.)
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.)
A rollback segment that is acquired exclusively by an instance when the instance opens a database.
An Oracle instance has two types of processes: User processes and Oracle processes.
A process monitor database process that performs process recovery when a user process fails. PMON is responsible for cleaning up the cache and freeing resources that the process was using. PMON also checks on dispatcher and server processes and restarts them if they have failed. As a part of service registration, PMON registers instance information with the listener.
A rollback segment that is available to any instance that requires a rollback segment.
A raw device is a disk drive that does not yet have a file system set up. Raw devices are used for Real Application Clusters since they enable the sharing of disks. See also raw partition.
A raw partition is 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 cooked partition. See also raw device.
In Real Application Clusters, if a session (reader) needs to read a data block that has been recently modified by another session in a different instance (writer), a concurrency control mechanism takes place to ensure read consistency. The contention resolution mechanism involves Cache Fusion.
An architecture that allows multiple instances to access a shared database of datafiles. Real Application Clusters is also a software component that provides the necessary cluster database scripts, initialization files, and datafiles needed for the Oracle Enterprise Edition and Real Application Clusters.
The Recovery Manager is 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 prompt or use the graphical user interface-based Oracle Enterprise Manager Backup Manager.
Redo files contain records of all changes made to data in the database buffer cache. Every Oracle database has a set of two or more redo log files. The set of redo log files for a database is collectively known as the database's redo log. A redo log is made up of redo entries (also called redo records). Each of these is a group of change vectors describing a single atomic change to the database. The primary function of the redo log is to record all changes made to data. Should a failure prevent modified data from being permanently written to the datafiles, the changes can be obtained from the redo log and work is never lost. Redo log files are critical in protecting a database against failures. To protect against a failure involving the redo log itself, Oracle allows a multiplexed redo log so that two or more copies of the redo log can be maintained on different disks.
A hardware architecture that combines multiple hard disk drives to allow rapid access to a large volume of stored data.
A database based on the relational model developed by E.F. Codd. A relational database allows the definition of data structures, storage and retrieval operations and integrity constraints. In such a database the data and relations between them are organized in tables. A table is a collection of records and each record in a table contains the same fields. Certain fields can be designated as keys. This means that searches for specific values of that field will use indexing to speed them up.
A public IP address that is started by a Oracle Real Application Clusters Guard pack. A relocatable IP address can be moved among nodes to ensure that it is always available. This eliminates TCP/IP timeouts for new connections after a failover.
A repository database is a set of tables in an Oracle database that stores data required by Oracle Enterprise Manager. This database is separate from the database on the nodes.
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.
Resource affinity is the use of dynamic resource remastering to move the location of the resource masters for a database file to the instance where block operations are most frequently occurring. This optimizes the system in situations where update transactions are being executed on one instance. When activity shifts to another instance the resource affinity will correspondingly move to the new instance. If activity is not localized, then the resource ownership is hashed to the instances.
A concurrency control that defines global access rights for instances in a cluster.
A concurrency control that defines whether a data block is cached in only one instance (local) or if it cached in multiple instances (global).
A configuration in which each node serves as a primary node and also as a secondary node for another node, forming a closed ring.
Rollback segments are records of old values of data that were changed by each transaction (whether committed or not committed). Rollback segments are used to provide read consistency, to roll back transactions, and to recover the database. Each node typically has two rollback segments, that are identified with a naming convention of RBSthread_id_rollback_number by the
ROLLBACK_SEGMENTS parameter in the initsid.ora file.
A synonym for record. One row of data in a database table, having values for one or more columns. Outside the context of this manual, the term row is also defined as one set of field values in the output of query.
The memory that stores recently accessed data for an individual record (or row). Row caches are used so that subsequent requests for the data held in the same row can be processed more quickly.
See shared (S) mode.
Scalability is the ability to add additional nodes to Real Application Clusters applications and achieve markedly improved performance.
The factor that expresses how much more work can be done in the same time period by a larger system. the factor that expresses how much more work can be done in the same time period by a larger system. (See also: speed up.)
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.)
An enqueue utilized by a session when it needs a sequence value.
Server Management (SRVM) is a component of Oracle Enterprise Manager. It is a comprehensive and integrated system management solution for Real Application Clusters. SRVM enables you to manage multiinstance databases that run in heterogeneous environments through an open client/server architecture.
In addition to managing cluster databases, SRVM enables you to schedule jobs, perform event management, monitor performance, and obtain statistics to tune cluster databases. Note that SRVM is not a separate product. It is an integral part of Oracle Enterprise Manager.
A service name is 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, initdbname.ora.
The service name is included in the
CONNECT_DATA part of the connect descriptor.
A feature whereby the process monitor (PMON) 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:
The session address (Saddr) is the dotted notation locator for a current session. The Saddr number is displayed in both the Cluster Database Session Chart and in the
V$SESSION dynamic performance view.
SETLINKS is a utility used to map symbolic links to raw devices for Windows NT and Windows 2000.
The buffer state name for a shared resource.
Shared is a protected read resource mode. No writes are allowed in shared mode. In shared mode, any number of users can have simultaneous read access to a resource. (See also: exclusive (X) mode and null (N) mode.)
The aggregation of the buffer caches of all instances in a cluster database.
A server that is configured to allow many user processes to share very few server processes, so that the number of users that can be supported is increased. With shared server configuration, many user processes connect to a dispatcher. The dispatcher directs multiple incoming network session requests to a common queue. An idle shared server process from a shared pool of server processes picks up a request from the queue. This means a small pool of server processes can serve a large amount of clients. A shared server is in contrast with a dedicated server.
The concept that more hardware can perform the same task in less time than the original system. With added hardware, speed up holds the task constant and measures time savings. (See also: scale up.)
Real Application Clusters can use the Service Control (SRVCTL) utility to manage instances. SRVCTL is installed on each node. The SRVCTL utility gathers information about all the instances for Oracle Enterprise Manager. SRVCTL acts as a single point of control between the Oracle Intelligent Agent and the nodes. Only one node's Oracle Intelligent Agent is used to communicate to SRVCTL. SRVCTL on that node then communicates to the other nodes through Java Remote Method Invocation (RMI).
See Oracle9i Data Guard.
Startup is an Operating System-Dependent component that provides one-time configuration to startup functionality.
A memory device that stores data. Usually a persistent storage that must be accessed by read/write transactions to alter its contents.
A high speed network of shared storage devices. Typically, SAN architecture allows access to all storage devices by all servers on a local area network (LAN) or wide are network (WAN). Most SANs conform to Fibre Channel standards.
SQL is an industry-standard language for creating, updating, and querying relational database management systems. The acronym SQL is spoken "sequel".
Two or more similar processors connected through a high-bandwidth link and managed by one operating system, where each processor has equal access to I/O devices. (See also: uniform memory access (UMA)
A logical time stamp that defines a committed version of a database at one point in time. Oracle assigns every committed transaction a unique SCN.
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.
The Oracle system identifier (SID) identifies a specific instance of the running Oracle software. For a Real Application Clusters database, each node within the cluster has an instance referencing the database.
The database name, specified by the
DB_NAME parameter in the
INITDB_NAME.ORA file, and unique thread ID make up each node's SID. The thread ID starts at 1 for the first instance in the cluster, and is incremented by 1 for the next instance, and so on.
The system monitor performs crash recovery when a failed instance starts up again. In Real Application Clusters, the SMON process of one instance can perform instance recovery for other instances that have failed. SMON also cleans up temporary segments that are no longer in use and recovers expired transactions that were skipped during crash and instance recovery because of file-read or offline errors. These transactions are eventually recovered by SMON when the tablespace or file is brought back online. SMON also coalesces free extents within the database's dictionary-managed tablespaces to make free space contiguous and easier to allocate.
Table locks are Database Mount Locks that protect entire tables. A transaction acquires a table resource when a table is modified by one of the following statements:
SELECT (with the
FOR UPDATE clause), and
LOCK TABLE. A table lock can be held in any of three modes: null (N) mode, shared (S) mode, and exclusive (X) mode.
A logical portion of an Oracle database used to allocate storage for data. Each tablespace corresponds to one or more physical datafiles. Every Oracle database has a tablespace called
SYSTEM and can have additional tablespaces. A tablespace is used to group related logical structures together. For example, tablespaces commonly group all of an application's objects to simplify certain administrative operations.
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.)
The tablespace of temporary tables or indexes created during the processing of an structured query language (SQL) statement.
Each Oracle instance has its own set of online redo log groups. These groups are called a thread of online redo. In non-Real Application Clusters environments, each database has only one thread that belongs to the instance accessing it. In 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.
A colloquial term for 99.9% system availability.
A file that contains net service names. This file is needed on clients, nodes, the Console, and the Oracle Performance Manager machine.
A list of blocks freed by uncommitted transactions.
Transaction systems are application systems that are characterized by updates to the database. Examples of transaction systems include e-business systems and ERP applications. More specialized examples include telephone call and billing systems, credit card transactions, and airline reservation systems. Transaction systems are also known as Online Transaction Processing (OLTP) systems.
In computer software, an action is transparent if it takes place without any effect visible to the user. Transparency is considered a good system characteristic because it shields the user from the system's complexity.
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.
TNS is a foundational technology, part of Oracle Names. TNS works with any standard network transport protocol. In other contexts, TNS is also used as an acronym for Transparent Network Services.
In uniform memory access configurations, or UMA, all processors can access main memory at the same speed. In this configuration, memory access is uniform. This configuration is also known as Symmetric Multi-Processor (SMP). (See also: non-uniform memory access (NUMA)
A computer with a single CPU.
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.)
Software that provides storage management for a Storage Area Network (SAN). Usually host-based Redundant Array of Independent Disks (RAID) software. Most volume managers use a graphical user interface (GUI) console to show the partitioning and status of storage volumes. Volume managers can create volumes from various disks, and those volumes can encompass multiple disks. (See also: raw partition.)
The process of transferring information about parsed structured query language (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.
See exclusive (X) mode.