It is a database commonly used for running online transaction processing (OLTP), data warehousing (DW) and mixed (OLTP & DW) database workloads.
The latest generation, Oracle Database 19c, is available on-prem, on-cloud, or in a hybrid-Cloud environment. 19c may also be deployed on Oracle Engineered Systems (e.g. Exadata) on-prem, on Oracle (public) cloud or (private) cloud at customer. At Openworld 2017 in San Francisco, Executive Chairman of the Board and CTO, Larry Ellison announced the next database generation, Oracle Autonomous Database.
Larry Ellison and his two friends and former co-workers, Bob Miner and Ed Oates, started a consultancy called Software Development Laboratories (SDL) in 1977. SDL developed the original version of the Oracle software. The name Oracle comes from the code-name of a CIA-funded project Ellison had worked on while formerly employed by Ampex.
Releases and versions
Oracle products follow a custom release-numbering and -naming convention.
The "c" in the current release, Oracle Database 19c, stands for "Cloud".
Previous releases (e.g. Oracle Database 10g and Oracle9i Database) have used suffixes of "g" and "i" which stand for "Grid" and "Internet" respectively.
Prior to the release of Oracle8i Database, no suffixes featured in Oracle Database naming conventions.
|Oracle Database Version||Initial Release Version||Initial Release Date||Terminal Patchset Version||Terminal Patchset Date||Marquee Features|
|Old version, no longer supported:Oracle v2||2.3||1979||First commercially available SQL-based RDBMS|
|Old version, no longer supported:Oracle v3||3.1.3||1983||Concurrency control, data distribution, andscalability|
|Old version, no longer supported:Oracle v4||184.108.40.206||1984||220.127.116.11||Multiversion read consistency.First version available forMS-DOS.|
|Old version, no longer supported:Oracle v5||5.0.22 (5.1.17)||1985||5.1.22||Support forclient/server computinganddistributed database systems.First version available forOS/2.|
|Old version, no longer supported:Oracle v6||6.0.17||1988||6.0.37||Row-level locking, scalability, online backup and recovery,PL/SQL.First version available forNovell Netware 386.|
|Old version, no longer supported:Oracle 6.2||6.2.0||Oracle Parallel Server|
|Old version, no longer supported:Oracle7||7.0.12||June 1992||PL/SQL stored procedures, Triggers, Distributed 2-phase commit, Shared Cursors, Cost Based Optimizer|
|Old version, no longer supported:Oracle 7.1||7.1.0||May 1994||Parallel SQL Execution|
|Old version, no longer supported:Oracle 7.2||7.2.0||May 1995||Shared Server, XA Transactions, Transparent Application Failover|
|Old version, no longer supported:Oracle 7.3||7.3.0||February 1996||7.3.4||Object-relational database|
|Old version, no longer supported:Oracle8 Database||8.0.3||June 1997||8.0.6||Recovery Manager, Partitioning.First version available for Linux.|
|Old version, no longer supported:Oracle8iDatabase||18.104.22.168||1998||22.214.171.124||August 2000||Native internet protocols and Java, Virtual Private Database|
|Old version, no longer supported:Oracle9iDatabase||126.96.36.199||2001||188.8.131.52||December 2003||Oracle Real Application Clusters (RAC), Oracle XML DB|
|Old version, no longer supported:Oracle9iDatabase Release 2||184.108.40.206||2002||220.127.116.11||April 2007||Advanced Queuing,Data Mining, Streams, Logical Standby|
|Old version, no longer supported:Oracle Database 10gRelease 1||10.1.0.2||2003||10.1.0.5||February 2006||Automated Database Management, Automatic Database Diagnostic Monitor, Grid infrastructure, Oracle ASM, Flashback Database|
|Old version, no longer supported:Oracle Database 10gRelease 2||10.2.0.1||July 2005||10.2.0.5||April 2010||Real Application Testing, Database Vault, Online Indexing, Advanced Compression, Data Guard Fast-Start Failover, Transparent Data Encryption|
|Old version, no longer supported:Oracle Database 11gRelease 1||18.104.22.168||September 2007||22.214.171.124||September 2008||Active Data Guard, Secure Files,Exadata|
|Old version, no longer supported:Oracle Database 11gRelease 2||126.96.36.199||September 2009||188.8.131.52||August 2013||Edition Based Redefinition, Data Redaction, Hybrid Columnar Compression, Cluster File System, Golden Gate Replication,Database Appliance|
|Old version, no longer supported:Oracle Database 12cRelease 1||184.108.40.206||July 2013||220.127.116.11||July 2014||Multitenant architecture, In-MemoryColumn Store, NativeJSON, SQL Pattern Matching, Database Cloud Service|
|Older version, yet still supported:Oracle Database 12cRelease 2||18.104.22.168||September 2016 (cloud) March 2017 (on-prem)||Native Sharding, Zero Data Loss Recovery Appliance, Exadata Cloud Service, Cloud at Customer|
|Older version, yet still supported:Oracle Database 18c||18.1.0||February 2018 (cloud: 18.1.0)July 2018 (on-prem: 18.3.0)||Polymorphic Table Functions, Active Directory Integration|
|Current stable version:Oracle Database 19c||19.0.0||February 2019 (Exadata) April 2019 (Linux and other platforms) June 2019 (cloud) August 2019 (most recent patch set)||Active Data Guard DML Redirection, Automatic Index Creation, Real-Time Statistics Maintenance, SQL Queries on Object Stores, In-Memory for IoT Data Streams, and many more.|
Patch updates and security alerts
Oracle Database deployment
Oracle Database may be licensed and deployed on-premises on a choice of platforms including Oracle Engineered Systems, and on-Cloud with a choice of services running on general purpose hardware or Exadata. The various editions and Cloud services provide different levels of database functionality for different use cases (e.g. dev/test, departmental and non-critical apps, mission-critical workloads) with different levels of performance, availability, etc. service levels.
Oracle Database Cloud Services: for on-Cloud and Cloud at Customer deployments
Oracle Database editions: mainly for on-prem deployments
Engineered systems such as Oracle Exadata specifically built for Oracle Database deployment (on-prem, on-Cloud, Cloud at Customer)
Database Cloud Services
Oracle Corporation provides a range of database cloud services on its Oracle Cloud platform that are designed for different database use cases; from test/dev deployments to small and medium sized workloads to large mission-critical workloads. Oracle Database Cloud Services are available on a choice of general purpose hardware and Exadata engineered systems, in either virtual machines environments or 'bare metal' infrastructure (now known as Oracle Cloud Infrastructure).
As of 2017, the latest Oracle Database version (22.214.171.124) comes in three editions for on-premises deployments:
Oracle Database Enterprise Edition (EE): offers industry-leading scalability and reliability in both clustered and single system configurations and imposes no limitation on server resources available to the database.
Oracle Database Standard Edition 2 (SE2): intended for small- to medium-sized implementations, SE2 includes Real Application Clusters and may be deployed on servers or clusters with a maximum of 2 sockets total and capped to use a maximum of 16 concurrent user threads. SE2 uses the same code base as EE, and therefore upwardly compatible and simple to upgrade to EE.
Oracle Database Personal Edition (PE): A single-user, single-machine development and deployment license that allows use of all database features. PE is upwardly compatible to SE2 and EE.
Oracle Corporation also makes the following edition available:
Oracle Database Express Edition (XE) , a free-to-use entry-level version of Oracle Database available for Windows and Linux platforms. The current version, Oracle Database 18c XE is automatically resource limited up to 2 CPUs, up to 2 GB of RAM and storing up to 12 GB of user data. It provides a subset of EE functionality (not including features such as managed backup and recovery, high availability and replication), is community-supported and comes with its own license terms. XE was first introduced in 2005 with Oracle Database 10g Release 2 with a limitation to a maximum of 1 CPU, 1 GB of RAM and 4 GB of user data. Oracle Database 11g XE was released on 24 September 2011, and increased user data capacity to 11 GB. Oracle Database 18c XE was released on the 20th of October 2018, increasing capacity to 2 CPUs, 2 GB of RAM and 12 GB of user data.
Up to (and including) Oracle Database 12c release 126.96.36.199, Oracle also offered the following:
Oracle Database Standard Edition (SE) for single or clustered servers with a maximum capacity of 4 CPU sockets.
It was largely the same as the current SE2 edition and included Real Application Clusters for use on server clusters with a maximum of 4 CPU sockets.
Oracle Standard Edition One (SE1), was first introduced with Oracle Database 10g. It offered the same features as SE and was licensed to run on single servers with a maximum of 2 CPU sockets.
Oracle Corporation discontinued SE and SE1 with the 188.8.131.52 release, and stopped offering new licenses for these editions on December 1, 2015.
Oracle Database 12c is supported on the following OS and architecture combinations:
In 2008, Oracle Corporation announced the availability of Oracle Exadata Database Machine (V1), the first generation of Engineered Systems specifically designed for Oracle Database workloads.
In 2011, Oracle Corporation announced the availability of Oracle Database Appliance, a pre-built, pre-tuned, highly available clustered database server built using two SunFire X86 servers and direct attached storage.
Database options and features
The Oracle Database offers a wide range of options and features in the areas of Availability, Scalability, Analytics, Performance, Security, Management, Developers and Integration.
These aim to enhance and complement existing database functionality to meet customer-specific requirements. All Database Options are only available for Enterprise Edition and offered for an extra cost. An exception to these two rules is Oracle Real Application Clusters option, which comes included with Oracle Database 12c Standard Edition 2 at no additional cost.
Oracle Active Data Guard  extends Oracle Data Guard functionality with advanced features, allowing read-only access to data in a physical standby database to offload primary of such tasks as reporting, ad-hoc queries, data extraction and backup, offloading redo transport and minimizing standby impact on commit response times (using Far Sync feature), providing option for rolling upgrades for non-RAC customers, managing clients workload across replicated database and improving automated service failover (using Global Data Services), etc.
Oracle Real Application Clusters (RAC) is the computer cluster version of Oracle Database.
Oracle RAC One Node  is a one-node version of Oracle Real Application Clusters, providing capabilities for database failover and high availability in the form of rolling upgrades, online instance migration, application continuity and automated quality of service management.
Oracle Advanced Analytics  allows access to in-database data mining algorithms and use of Oracle R Enterprise functionality, an integration with open-source R statistical programming language and environment.
Oracle Partitioning  allows partitioning of tables and indices, where large objects are stored in database as a collection of individual smaller pieces at the same time appearing on application level as a uniform data object.
Oracle On-Line Analytical Processing (OLAP)  is Oracle implementation of online analytical processing.
Oracle data models: pre-built data models with database analytics and business intelligence capabilities for specific industries including Retail Data Model Communications Data Model Airlines Data Model Utilities Data Model
Oracle Advanced Compression  complements Enterprise Edition basic table compression feature with comprehensive data compression and Information Lifecycle Management capabilities, including those specifically tailored to Oracle's engineered systems, like Oracle Exadata.
Oracle Database In-Memory , an in-memory, column-oriented data store, has been seamlessly integrated into the Oracle Database. This technology aims to improve the performance of analytic workloads without impacting the performance of transactions that continue to use Oracle's traditional row format in memory. The product's performance comes through the in-memory, columnar compressed format and through the use of SIMD vector processing (Single Instruction processing Multiple Data values). In-Memory Aggregation improves performance of typical analytic queries using efficient in-memory arrays for joins and aggregation.
Oracle Real Application Testing enable testing of system changes in a simulation of production-level workload and use.
Oracle TimesTen Application-Tier Database Cache  allows caching subsets of a database in the application tier for improved response time.
It is built using Oracle TimesTen In-Memory Database.
Oracle Advanced Security  provides Transparent Data Encryption and Data Redaction security features, the former allowing encryption of data stored in a database (all or a subset of it), exported using Data Pump, or backed up using Oracle Recovery Manager, and the latter allowing redaction of sensitive database data (e.g., credit card or social security numbers) returned to database applications.
Oracle Database Vault  enforces segregation of duties, principle of least privilege and other data access controls, allowing protection of application data from access by privileged database users.
Oracle Label Security  is a sophisticated and flexible framework for a fine-grained label based access control (LBAC) implementation.
Oracle Multitenant  is the capability that allows database consolidation and provides additional abstraction layer. In a Multitenant configuration, one Oracle database instance known as "container database" (CDB) acts as a federated database system for a collection of up to 252 distinct portable collections of database objects, referred to as "pluggable databases" (PDB), each appearing to an outside client as a regular non-CDB Oracle database.
Management Packs: integrated set of Oracle Enterprise Manager tools for maintaining various aspects of Oracle Database including: Diagnostics Pack Tuning Pack Database Lifecycle Management Pack Data Masking and Subsetting Pack Cloud Management Pack for Oracle Database
Oracle GoldenGate 11g  (distributed real-time data acquisition)
Apart from the clearly defined database options, Oracle databases may include many semi-autonomous software sub-systems, which Oracle Corporation sometimes refers to as "features" in a sense subtly different from the normal use of the word.
For example, Oracle Data Guard counts officially as a feature, but the command-stack within SQL*Plus, though a usability feature, does not appear in the list of "features" in Oracle's list . Such "features" may include (for example):
Automatic Storage Management
Data Aggregation and Consolidation 
Data Guard  for high availability
Generic Connectivity  for connecting to non-Oracle systems.
Fast-start parallel rollback
Flashback for selective data recovery and reconstruction
Heterogeneous Services (HS), providing connectivity to non-Oracle systems and code.
Oracle Data Access Components (ODAC), tools that consist of: Oracle Data Provider for.NET
(ODP.NET) Oracle Developer Tools (ODT) for Visual Studio Oracle Providers for ASP.NET
Oracle Database Extensions for.NET Oracle
Provider for OLE DB Oracle Services for Microsoft Transaction Server
Oracle-managed files  (OMF) – a feature allowing automated naming, creation and deletion of datafiles at the operating-system level.
Recovery Manager  (RMAN) for database backup, restoration and recovery
SQLPlus, a program that allows users to interact with Oracle database(s) via SQL and PL/SQL commands on a command-line. Compare iSQLPlus
SQLcl, a command-line interface for queries, developed on the basis of Oracle SQL Developer
Universal Connection Pool (UCP), a connection pool based on Java and supporting JDBC, LDAP, and JCA
Oracle Application Express, a no-cost environment for database-oriented software-development
Oracle Text uses standard SQL to index, search, and analyze text and documents stored in the Oracle database.
Oracle database provides a long list of supported data models that can be used and managed inside Oracle database:
Simple Oracle Document Access (SODA)  offers a set of NoSQL-style APIs to store, query and index JSON documents in the database, without needing to know Structure Query Language (SQL) or how Document Collections are stored in the database.
Oracle Spatial and Graph Oracle Database provides native support for managing spatial and location data Oracle Locator – a freely-available subset of Oracle Spatial and Graph
Oracle Text, a no-cost component in each edition of the database.
It provides native support for managing free text, in multiple languages inside the database.
Oracle Multimedia (known as "Oracle interMedia" before Oracle 11g) for storing and integrating multimedia data within a database
Object-relational database support, a no-cost component in each edition of the database. It provides native support for objects inside the database.
Oracle Corporation classifies as "utilities" bundled software supporting data transfer, data maintenance and database administration.
Utilities included in Oracle database distributions include:
As of 2007 Oracle Corporation had started a drive toward "wizard"-driven environments with a view to enabling non-programmers to produce simple data-driven applications.
The most popular application development tool that ships with Oracle Database is Oracle Application Express (APEX), a browser-based tool that allows developers to build responsive, database-driven applications, leveraging their SQL and PL/SQL skills.
Oracle SQL Developer, a free graphical tool for database development, allows developers to browse database objects, to run SQL statements and SQL scripts, and to edit and debug PL/SQL statements. It incorporates standard and customized reporting.
Users can also develop their own applications in Java and in PL/SQL, optionally using tools such as:
JAccelerator (NCOMP) – a native-compilation Java "accelerator", integrates hardware-optimized Java code into an Oracle 10g database.
Oracle Live SQL makes available a test environment for Oracle Database users.
Programming language APIs
Oracle Database can be accessed from many programming languages and environments.
Java via JDBC, SQLJ 
Node.js via node-oracledb 
Python via cx_Oracle 
PHP via PHP OCI8, PDO_OCI
R via ROracle 
Erlang via erloci 
COBOL via Pro*COBOL 
SAS via SAS/ACCESS(R) for Relational Databases 
Java based languages like Scala can use JDBC to access Oracle Database.
Database support options
Users who have Oracle support contracts can use Oracle's "My Oracle Support" or "MOS" web site – known as "MetaLink" until a re-branding exercise completed in October 2010.
The support site provides users of Oracle Corporation products with a repository of reported problems, diagnostic scripts and solutions.
It also integrates with the provision of support tools, patches and upgrades.
The Remote Diagnostic Agent or RDA  can operate as a command-line diagnostic tool executing a script. The data captured provides an overview of the Oracle Database environment intended for diagnostic and trouble-shooting. Within RDA, the HCVE (Health Check Validation Engine) can verify and isolate host system environmental issues that may affect the performance of Oracle software.
Oracle Corporation also endorses certain practices and conventions as enhancing the use of its database products.
Oracle Maximum Availability Architecture (MAA) guidelines on developing high-availability systems
Optimal Flexible Architecture (OFA), blueprints for mapping Oracle-database objects to file-systems
Oracle Certification Program
The Oracle Certification Program, a professional certification program, includes the administration of Oracle Databases as one of its main certification paths. It contains three levels:
Oracle Certified Associate (OCA)
Oracle Certified Professional (OCP)
Oracle Certified Master (OCM)
A large number of User Groups for Oracle Database administrators, developers and users has been established on geographical/region, industry and product basis, including:
In the market for relational databases, Oracle Database competes against commercial products such as IBM's DB2 UDB and Microsoft SQL Server. Oracle and IBM tend to battle for the mid-range database market on Unix and Linux platforms, while Microsoft dominates the mid-range database market on Microsoft Windows platforms. However, since they share many of the same customers, Oracle and IBM tend to support each other's products in many middleware and application categories (for example: WebSphere, PeopleSoft, and Siebel Systems CRM), and IBM's hardware divisions work closely with Oracle on performance-optimizing server-technologies (for example, Linux on z Systems). Niche commercial competitors include Teradata (in data warehousing and business intelligence), Software AG's ADABAS, Sybase, and IBM's Informix, among many others.
Increasingly, the Oracle database products compete against such open-source software relational database systems as PostgreSQL, MongoDB, and Couchbase. Oracle acquired Innobase, supplier of the InnoDB codebase to MySQL, in part to compete better against open source alternatives, and acquired Sun Microsystems, owner of MySQL, in 2010. Database products licensed as open source are, by the legal terms of the Open Source Definition, free to distribute and free of royalty or other licensing fees.
Oracle Database Cloud Services
- Customers can choose from a wide range of database services on Oracle Cloud that are available as 'pay as you go' hourly and monthly rates, and also have the option to re-use existing on-prem licenses on Oracle Cloud via a Bring Your Own License (BYOL) program.
Oracle Database On-Premise Licensing
- Prospective purchasers can obtain licenses for on-prem deployment based either on the number of processors in their target machines or on the("named users").The term "per processor" for Oracle Database Enterprise Edition is defined with respect to physical cores and a processor core multiplier (common processors = 0.5*cores). e.g. An 8-processor, 32-core server using Intel Xeon 56XX CPUs would require 16 processor licenses.:The low entry cost, Oracle Database Standard Edition 2 (SE2), includes Real Application Clusters and may be deployed on servers or clusters with a maximum of 2 sockets total and capped to use a maximum of 16.Oracle Database Express Edition (XE)(version released in 2005, production version released in February 2006), offers a free version of the Oracle RDBMS, but one limited to 11 GB of user data and to 1 GB of memory used by the database (SGA+PGA).XE uses no more than one CPU and lacks an internal.XE runs on 32-bit and 64-bit Windows and 64-bit Linux, but not on AIX, Solaris, HP-UX and the other operating systems available for other editions.Support is via a free Oracle Discussion Forumonly.
Physical and logical structures
An Oracle database system—identified by an alphanumeric system identifier or SID—comprises at least one instance of the application, along with data storage. An instance—identified persistently by an instantiation number (or activation id: SYS.V_$DATABASE.ACTIVATION#)—comprises a set of operating-system processes and memory-structures that interact with the storage. Typical processes include PMON (the process monitor) and SMON (the system monitor). Oracle documentation can refer to an active database instance as a "shared memory realm".
Users of Oracle databases refer to the server-side memory-structure as the SGA (System Global Area).
The SGA typically holds cache information such as data-buffers, SQL commands, and user information. In addition to storage, the database consists of online redo logs (or logs), which hold transactional history. Processes can in turn archive the online redo logs into archive logs (offline redo logs), which provide the basis for data recovery and for the physical-standby forms of data replication using Oracle Data Guard.
The Oracle RAC (Real Application Clusters) option uses multiple instances attached to a central storage array. In version 10g, grid computing introduced shared resources where an instance can use CPU resources from another node in the grid. The advantage of Oracle RAC is that the resources on both nodes are used by the database, and each node uses its own memory and CPU. Information is shared between nodes through the interconnect—the virtual private network.
The Oracle DBMS can store and execute stored procedures and functions within itself. PL/SQL (Oracle Corporation's proprietary procedural extension to SQL), or the object-oriented language Java can invoke such code objects and/or provide the programming structures for writing them.
The Oracle RDBMS stores data logically in the form of tablespaces and physically in the form of data files ("datafiles"). Tablespaces can contain various types of memory segments, such as Data Segments, Index Segments, etc. Segments in turn comprise one or more extents. Extents comprise groups of contiguous data blocks. Data blocks form the basic units of data storage.
The partitioning feature was introduced in Oracle 8. This allows the partitioning of tables based on different set of keys. Specific partitions can then be added or dropped to help manage large data sets.
Oracle database management tracks its computer data storage with the help of information stored in the SYSTEM tablespace. The SYSTEM tablespace contains the data dictionary, indexes and clusters. A data dictionary consists of a special collection of tables that contains information about all user-objects in the database. Since version 8i, the Oracle RDBMS also supports "locally managed" tablespaces that store space management information in bitmaps in their own headers rather than in the SYSTEM tablespace (as happens with the default "dictionary-managed" tablespaces). Version 10g and later introduced the SYSAUX tablespace, which contains some of the tables formerly stored in the SYSTEM tablespace, along with objects for other tools such as OEM, which previously required its own tablespace.
Disk files primarily represent one of the following structures:
Data and index files: These files provide the physical storage of data, which can consist of the data-dictionary data (associated with the tablespace SYSTEM), user data, or index data.
DBAs can manage these files manually or leave their administration to Oracle itself.
Note that a datafile has to belong to exactly one tablespace, whereas a tablespace can consist of multiple datafiles.
Redo log files, recording all changes to the database – used to recover from an instance failure.
Often, a database stores these files multiple times for extra security in case of disk failure.
Identical redo log files are associated in a "group".
Undo files: These special datafiles, which can only contain undo information, aid in recovery, rollbacks, and read-consistency.
Archive log files: These files, copies of the redo log files, are usually stored at different locations.
They are necessary (for example) when applying changes to a standby database, or when performing recovery after a media failure. One can store identical archive logs in multiple locations.
Tempfiles: These special datafiles serve exclusively for temporary storage data (used for example during large sorts or for global temporary tables)
Control files, necessary for database startup.
Oracle Corporation defines a control file as "[a] binary file that records the physical structure of a database and contains the names and locations of redo log files, the time stamp of the database creation, the current log sequence number, checkpoint information, and so on".
At the physical level, data files comprise one or more data blocks, where the block size can vary between data files.
Most Oracle database installations come with a default schema called SCOTT. After the installation process sets up sample tables, the user logs into the database with the username scott and the password tiger. The name of the SCOTT schema originated with Bruce Scott, one of the first employees at Oracle (then Software Development Laboratories), who had a cat named Tiger.
Oracle Corporation now de-emphasizes the SCOTT schema, as it uses few features of more recent Oracle releases.
Most recent examples supplied by Oracle Corporation reference the default HR or OE schemas.
SYS (essential core database structures and utilities)
SYSTEM (additional core database structures and utilities, and privileged account)
OUTLN (used to store metadata for stored outlines for stable query-optimizer execution plans.)
BI, IX, HR, OE, PM, and SH (expanded sample schemas containing more data and structures than the older SCOTT schema).
System Global Area
Each Oracle instance uses a System Global Area or SGA—a shared-memory area—to store its data and control-information.
Each Oracle instance allocates itself an SGA when it starts and de-allocates it at shut-down time.
The information in the SGA consists of the following elements, each of which has a fixed size, established at instance startup:
Every Oracle database has one or more physical datafiles, which contain all the database data.
The data of logical database structures, such as tables and indexes, is physically stored in the datafiles allocated for a database.
Datafiles have the following characteristics:
One or more datafiles form a logical unit of database storage called a tablespace.
A datafile can be associated with only one tablespace.
Datafiles can be defined to extend automatically when they are full.
Data in a datafile is read, as needed, during normal database operation and stored in the memory cache of Oracle Database.
For example, if a user wants to access some data in a table of a database, and if the requested information is not already in the memory cache for the database, then it is read from the appropriate datafiles and stored in memory.
Modified or new data is not necessarily written to a datafile immediately.
To reduce the amount of disk access and to increase performance, data is pooled in memory and written to the appropriate datafiles all at once.
the redo log buffer: this stores redo entries—a log of changes made to the database.
The instance writes redo log buffers to the redo log as quickly and efficiently as possible.
The redo log aids in instance recovery in the event of a system failure.
the shared pool: this area of the SGA stores shared-memory structures such as shared SQL areas in the library cache and internal information in the data dictionary.
An insufficient amount of memory allocated to the shared pool can cause performance degradation.
the Large pool Optional area that provides large memory allocations for certain large processes, such as Oracle backup and recovery operations, and I/O server processes
Database buffer cache: Caches blocks of data retrieved from the database
KEEP buffer pool: A specialized type of database buffer cache that is tuned to retain blocks of data in memory for long periods of time
RECYCLE buffer pool: A specialized type of database buffer cache that is tuned to recycle or remove block from memory quickly
nK buffer cache: One of several specialized database buffer caches designed to hold block sizes different from the default database block size
Java pool:Used for all session-specific Java code and data in the Java Virtual Machine (JVM)
Streams pool: Used by Oracle Streams to store information required by capture and apply
The library cache stores shared SQL, caching the parse tree and the execution plan for every unique SQL statement.
If multiple applications issue the same SQL statement, each application can access the shared SQL area.
This reduces the amount of memory needed and reduces the processing-time used for parsing and execution planning.
Data dictionary cache
The data dictionary comprises a set of tables and views that map the structure of the database.
Oracle databases store information here about the logical and physical structure of the database.
The data dictionary contains information such as:
user information, such as user privileges
integrity constraints defined for tables in the database
names and datatypes of all columns in database tables
information on space allocated and used for schema objects
The Oracle instance frequently accesses the data dictionary to parse SQL statements. Oracle operation depends on ready access to the data dictionary—performance bottlenecks in the data dictionary affect all Oracle users. Because of this, database administrators must make sure that the data dictionary cache has sufficient capacity to cache this data. Without enough memory for the data-dictionary cache, users see a severe performance degradation. Allocating sufficient memory to the shared pool where the data dictionary cache resides precludes this particular performance problem.
Program Global Area
The size and content of the PGA depends on the Oracle-server options installed.
This area consists of the following components:
stack-space: the memory that holds the session's variables, arrays, and so on
session-information: unless using the multithreaded server, the instance stores its session-information in the PGA.
In a multithreaded server, the session-information goes in the SGA.
private SQL-area: an area that holds information such as bind-variables and runtime-buffers
sorting area: an area in the PGA that holds information on sorts, hash-joins, etc.
DBAs can monitor PGA usage via the system view.
Dynamic performance views
The dynamic performance views (also known as "fixed views") within an Oracle database present information from virtual tables (X$ tables) built on the basis of database memory. Database users can access the V$ views (named after the prefix of their synonyms) to obtain information on database structures and performance.
The Oracle RDBMS typically relies on a group of processes running simultaneously in the background and interacting to monitor and expedite database operations. Typical operating environments might include – temporarily or permanently – some of the following individual processes (shown along with their abbreviated nomenclature):
advanced queueing processes (Qnnn)
archiver processes (ARCn)
checkpoint process (CKPT) REQUIRED
coordinator-of-job-queues process (CJQn): dynamically spawns slave processes for job-queues
database writer processes (DBWn) REQUIRED
Data Pump master process (DMnn)
Data Pump worker processes (DWnn)
dispatcher processes (Dnnn): multiplex server-processes on behalf of users
main Data Guard Broker monitor process (DMON)
job-queue slave processes (Jnnn)
log-writer process (LGWR) REQUIRED
log-write network-server (LNSn): transmits redo logs in Data Guard environments
logical standby coordinator process (LSP0): controls Data Guard log-application
media-recovery process (MRP): detached recovery-server process
memory-manager process (MMAN): used for internal database tasks such as Automatic Shared Memory Management (ASMM)
memory-monitor process (MMON): process for automatic problem-detection, self-tuning and statistics-gathering
memory-monitor light process (MMNL): gathers and stores Automatic Workload Repository (AWR) data
mmon slaves (Mnnnn—M0000, M0001, etc.): background slaves of the MMON process
netslave processes (NSVn): Data Guard Broker inter-database communication processes
parallel query execution servers (Pnnn)
process-monitor process (PMON) REQUIRED
process-spawner process (PSP0): spawns Oracle background processes after initial instance startup
queue-monitor coordinator process (QMNC): dynamically spawns queue monitor slaves
queue-monitor processes (QMNn)
recoverer process (RECO)
remote file-server process (RFS): in Oracle Data Guard, a standby recipient of primary redo-logs
monitor for Data Guard management (RSM0): Data Guard Broker Worker process
shared server processes (Snnn): serve client-requests
space-management coordinator process (SMCO): coordinates space management (from release 11g)
system monitor process (SMON) REQUIRED
User processes, connections and sessions
Oracle Database terminology distinguishes different computer-science terms in describing how end-users interact with the database:
Concurrency and locking
DML locks (or data locks) protect data
System locks (including latches, mutexes and internal locks) protect internal database structures like data files.
DDL locks (or data dictionary locks) protect the structure of schema objects.
Note: over the course of multiple releases Oracle has reduced the number of instances where an exclusive DDL lock is required when making changes to schema objects.
Non-blocking ddl's added as of 11.2
CREATE INDEX online
ALTER INDEX rebuild online
ALTER TABLE add column not null with default value
ALTER TABLE add constraint enable no validate
ALTER TABLE modify constraint validate
ALTER TABLE add column (without any default)
ALTER INDEX visible / invisible
ALTER INDEX parallel / no parallel
Non-blocking ddl's added to the list in 12.1
DROP INDEX online (backported to 11.2)
ALTER TABLE set unused column online
ALTER TABLE drop constraint online
ALTER INDEX unusable online
ALTER TABLE modify column visible / invisible
ALTER TABLE move partition / sub-partition online
ALTER TABLE add nullable column with default value
Non-blocking ddl's added to the list in 12.2
ALTER TABLE split partition [sub-partition] online
ALTER TABLE move online (move of a non-partitioned table)
ALTER TABLEe modify partition by.. online (to convert a non-partitioned table to partitioned state)
Non-blocking ddl's added to the list in 18.1
ALTER TABLE merge partition online
ALTER TABLE modify partition by.. online (to change the partitioning schema of a table)
Database administrators control many of the tunable variations in an Oracle instance by means of values in a parameter file.
This file in its ASCII default form ("pfile") normally has a name of the format init
The default binary equivalent server parameter file ("spfile") (dynamically reconfigurable to some extent)
defaults to the format spfile
The Oracle DBMS kernel code depends on C programming. Database administrators have limited access to Oracle-internal C structures via V$ views and their underlying X$ "tables".
The "Scheduler" (DBMS_SCHEDULER package, available from Oracle 10g onwards) and the "Job" subsystems (DBMS_JOB package) permit the automation of predictable processing.
Oracle Corporation has stated in product announcements that manageability for DBAs improved from Oracle9i to 10g.
Lungu and Vătuiu (2008) assessed relative manageability by performing common DBA tasks and measuring timings.
 They performed their tests on a single Pentium CPU (1.7 GHz) with 512 MB RAM, running Windows Server 2000.
From Oracle9i to 10g, installation improved 36%, day-to-day administration 63%, backup and recovery 63%, and performance diagnostics and tuning 74%, for a weighted total improvement of 56%.
The researchers concluded that "Oracle10g represents a giant step forward from Oracle9i in making the database easier to use and manage".
Logging and tracing
Various file-system structures hold logs and trace files, which record different aspects of database activity. Configurable destinations for such records can include:
Oracle Net Services allow client or remote applications to access Oracle databases via network sessions using various protocols.
Oracle Database software comes in 63 language-versions (including regional variations such as British English and American English).
Variations between versions cover the names of days and months, abbreviations, time-symbols (such as A.M. and A.D.), and sorting.
Oracle Corporation has translated Oracle Database error-messages into Arabic, Catalan, Chinese, Czech, Danish, Dutch, English, Finnish, French, German, Greek, Hebrew, Hungarian, Italian, Japanese, Korean, Norwegian, Polish, Portuguese, Romanian, Russian, Slovak, Spanish, Swedish, Thai and Turkish.
Comparison of relational database management systems
Comparison of object-relational database management systems
Database management system
List of relational database management systems
List of databases using MVCC