Oracle Database (commonly referred to as Oracle RDBMS or simply Oracle) is a relational database management system (RDBMS) produced and marketed by Oracle Corporation. As of 2008, Oracle had become a major presence in database computing.
Larry Ellison and his friends and former co-workers Bob Miner and Ed Oates started the consultancy 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 previously employed by Ampex.
Physical and logical structuring in Oracle
An Oracle database system 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).
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 (which hold transactional history). Processes can in turn archive the online redo logs into archive logs (offline redo logs), which provide the basis (if necessary) for data recovery and for some forms of data replication.
The Oracle RDBMS stores data logically in the form of tablespaces and physically in the form of data files. Tablespaces can contain various types of memory segments; for example, 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. At the physical level, data-files comprise one or more data blocks, where the block size can vary between data-files.
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 — and often (by default) 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 which can store space management information in bitmaps in their own headers rather than in the
SYSTEM tablespace (as happens with the default "dictionary-managed" tablespaces).
If the Oracle database administrator has instituted Oracle RAC (Real Application Clusters), then multiple instances, usually on different servers, attach to a central storage array. This scenario offers numerous advantages, most importantly performance, scalability and redundancy. However, support becomes more complex, and many sites do not use RAC. In version 10g, grid computing has introduced shared resources where an instance can use (for example) CPU resources from another node (computer) in the grid.
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.
Oracle database conventions refer to defined groups of ownership (generally associated with a "username") as schemas
Most Oracle database installations traditionally come with a default schema called
SCOTT. After the installation process has set up the sample tables, the user can log 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.
SCOTT schema has seen less use as it uses few of the features of the more recent releases of Oracle. Most recent examples reference the default HR or OE schemas.
Other default schemas include:
(essential core database structures and utilities)
(additional core database structures and utilities, and privileged account)
OUTLN (utilized to store metadata for stored outlines for stable query-optimizer execution plans .
SH (expanded sample schemas containing more data and structures than the older
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:
- the database buffer cache: this stores the most recently-used data blocks. These blocks can contain modified data not yet written to disk (sometimes known as "dirty blocks"), unmodified blocks, or blocks written to disk since modification (sometimes known as clean blocks). Because the buffer cache keeps blocks based on a most-recently-used algorithm, the most active buffers stay in memory to reduce I/O and to improve performance.
- 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 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 in order to parse SQL statements. The operation of Oracle depends on ready access to the data dictionary: performance bottlenecks in the data dictionary affect all Oracle users. Because of this, database administrators should 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 these particular performance problems.
Program Global Area
The Program Global Area or PGA memory-area contains data and control-information for Oracle's server-processes.
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 in the PGA which holds information such as bind-variables and runtime-buffers.
- sorting area: an area in the PGA which holds information on sorts, hash-joins, etc.
The Oracle RDBMS typically relies on a group of processes running simultaneously in the background and interacting to further and monitor database operations. Such processes (and their standard abbreviations) can include:
- archiver processes (ARCn)
- checkpoint process (CKPT)
- database writer processes (DBWn)
- dispatcher processes (Dnnn): multiplex server-processes on behalf of users
- memory-manager process (MMAN): used for internal database tasks such as Automatic Shared Memory Management
- job-queue processes (CJQn)
- log-writer process (LGWR)
- 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-monitor process (MMON)
- memory-monitor light process (MMNL): gathers and stores Automatic Workload Repository (AWR) data
- process-monitor process (PMON)
- process-spawner (PSP0): spawns Oracle processes
- queue-monitor processes (QMNn)
- recoverer process (RECO)
- remote file-server process (RFS)
- shared server processes (Snnn): serve client-requests
- system monitor process (SMON)
User processes, connections and sessions
Oracle Database terminology distinguishes different computer-science terms in describing how end-users interact with the database:
- user processes involve the invocation of application software
- a connection refers to the pathway linking a user process to an Oracle instance
- sessions consist of specific connections to an Oracle instance
Oracle Database software comes in 63 language-versions (including regional variations such as American and British). 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.
- 1979: Larry Ellison and friends founded Software Development Laboratories.
- 1979: SDL changed its company-name to "Relational Software, Inc." (RSI) and introduced its product Oracle V2 as an early commercially-available relational database system. The version did not support transactions, but implemented the basic SQL functionality of queries and joins. (RSI never released a version 1 - instead calling the first version version 2 as a marketing gimmick.)
- 1982: RSI in its turn changed its name, becoming known as "Oracle Corporation", to align itself more closely with its flagship product.
- 1983: The company released Oracle version 3, which it had re-written using the C programming language and which supported
ROLLBACK functionality for transactions. Version 3 extended platform support from the existing Digital VAX/VMS systems to include Unix environments.
- 1984: Oracle Corporation released Oracle version 4, which supported read-consistency.
- 1985: the Oracle RDBMS began supporting the client-server model, with networks becoming more widely available in the mid-1980s. Oracle version 5.0 supported distributed queries.
- 1988: Oracle RDBMS version 6 came out with support for PL/SQL embedded within Oracle Forms v3 (version 6 could not store PL/SQL in the database proper), row-level locking and hot backups.
- 1989: Oracle Corporation entered the application products market and developed its ERP product, (later to become part of the Oracle E-Business Suite), based on the Oracle relational database.
- 1990: the release of Oracle Applications release 8
- 1992: Oracle version 7 appeared with support for referential integrity, stored procedures and triggers.
- 1997: Oracle Corporation released version 8, which supported object-oriented development and multimedia applications.
- 1999: The release of Oracle8i aimed to provide a database inter-operating better with the Internet (the i in the name stands for "Internet"). The Oracle 8i database incorporated a native Java virtual machine (Oracle JVM).
- 2000: Oracle E-Business Suite 11i pioneers integrated enterprise application software
- 2001: Oracle9i went into release with 400 new features, including the ability to read and write XML documents. 9i also provided an option for Oracle RAC, or "Real Application Clusters", a computer-cluster database, as a replacement for the Oracle Parallel Server (OPS) option.
- 2003: Oracle Corporation released Oracle Database 10g. (The g stands for "grid"; emphasizing a marketing thrust of presenting 10g as "grid-computing ready".)
- 2005: Oracle Database 10.2.0.1 — also known as Oracle Database 10g Release 2 (10gR2) — appeared.
- 2006: Oracle Corporation announces Unbreakable Linux
- 2007: Oracle Database 10g Release 2 Sets New World Record TPC-H 3000 GB Benchmark Result
- 2007: Oracle Corporation released Oracle Database 11g for Linux and for Microsoft Windows.
- 2008: Oracle Corporation acquires BEA Systems.
Oracle products have historically followed their own release-numbering and naming conventions. With the Oracle RDBMS 10g release, Oracle Corporation started standardizing all current versions of its major products using the "10g" label, although some sources continued to refer to Oracle Applications Release 11i as Oracle 11i
. Major database-related products and some of their versions include:
Since version 7, Oracle's RDBMS release numbering has used the following codes:
- Oracle7: 7.0.16 — 7.3.4
- Oracle8 Database: 8.0.3 — 8.0.6
- Oracle8i Database Release 1: 184.108.40.206 — 220.127.116.11
- Oracle8i Database Release 2: 18.104.22.168 — 22.214.171.124
- Oracle8i Database Release 3: 126.96.36.199 — 188.8.131.52
- Oracle9i Database Release 1: 184.108.40.206 — 220.127.116.11 (patchset as of December 2003)
- Oracle9i Database Release 2: 18.104.22.168 — 22.214.171.124 (patchset as of April 2007)
- Oracle Database 10g Release 1: 10.1.0.2 — 10.1.0.5 (patchset as of February 2006)
- Oracle Database 10g Release 2: 10.2.0.1 — 10.2.0.4 (patchset as of April 2008)
- Oracle Database 11g Release 1: 126.96.36.199 — 188.8.131.52 (patchset as of September 2008)
The version-numbering syntax within each release follows the pattern: major.maintenance.application-server.component-specific.platform-specific.
For example, "10.2.0.1 for 64-bit Solaris" means: 10th major version of Oracle, maintenance level 2, Oracle Application Server (OracleAS) 0, level 1 for Solaris 64-bit.
The Oracle Administrator's Guide offers further information on Oracle release numbers. Oracle Corporation provides a table showing the latest patch-set releases by major release, operating-system, and hardware-architecture.
List of claimed firsts
Oracle Corporation claims to have provided:
Over and above the different versions of the Oracle database management software, Oracle Corporation subdivides its product into varying "editions" - apparently for marketing and license-tracking reasons. In approximate order of decreasing scale, we find:
- Enterprise Edition (EE) includes more features than the 'Standard Edition', especially in the areas of performance and security. Oracle Corporation licenses this product on the basis of users or of processors, typically for servers running 4 or more CPUs. EE has no memory limits, and can utilize clustering using Oracle RAC software.
- Standard Edition (SE) contains base database functionality. Oracle Corporation licenses this product on the basis of users or of processors, typically for servers running from one to four CPUs. If the number of CPUs exceeds 4 CPUs, the user must convert to an Enterprise license. SE has no memory limits, and can utilize clustering with Oracle RAC at no additional charge.
- Standard Edition One, introduced with Oracle 10g, has some additional feature-restrictions. Oracle Corporation markets it for use on systems with one or two CPUs. It has no memory limitations.
- Express Edition ('Oracle Database XE'), introduced in 2005, offers Oracle 10g free to distribute on Windows and Linux platforms (with a footprint of only 150 MB and restricted to the use of a single CPU, a maximum of 4 GB of user data and 1 GB of memory). Support for this version comes exclusively through on-line forums and not through Oracle support.
- Oracle Personal Edition provides the functionality of the "high end" Enterprise Edition but marketed to (and licensed for) single-user developers working on personal workstations.
- Oracle Database Lite, intended to run on mobile devices. The database, partially located on the mobile device, can synchronize with a server-based installation.
Prior to releasing Oracle9i, Oracle Corporation ported the database engine to a wide variety of platforms. More recently, Oracle Corporation has consolidated on a smaller range of operating system platforms.
As of October 2006, Oracle Corporation supported the following operating systems and hardware platforms for Oracle Database 10g:
- Apple Mac OS X Server: PowerPC
- HP HP-UX: PA-RISC, Itanium
- HP Tru64 UNIX: Alpha
- HP OpenVMS: Alpha, Itanium
- IBM AIX5L: IBM POWER
- IBM z/OS: zSeries
- Linux: x86, x86-64, PowerPC, zSeries, Itanium
- Microsoft Windows: x86, x86-64, Itanium
- Sun Solaris: SPARC, x86, x86-64
For links to some of Oracle Corporation's software which integrates with Oracle databases, see the Oracle Corporation
and the Oracle software
Oracle Corporation refers to some extensions to the core functionality of the Oracle database as "database options".
As of 2008
such options include:
In most cases, using these options entails extra licensing costs.
In addition to its RDBMS
, Oracle Corporation has released several related suites of tools and applications relating to implementations of Oracle databases. For example:
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 usage of the word.
Such "features" may include (for example):
Various tools address specific environments or specific market requirements.
Development of applications commonly takes place in Java (using Oracle JDeveloper) or through PL/SQL (using, for example, Oracle Forms and Oracle Reports). Oracle Corporation has started a drive toward 'wizard'-driven environments with a view to enabling non-programmers to produce simple data-driven applications.
Oracle SQL Developer, a free graphical tool for database development, allows developers to browse database objects, run SQL statements and SQL scripts, and edit and debug PL/SQL statements. It incorporates standard and customized reporting.
The Oracle GUI Oracle GUI site offers free downloads of Navicat Oracle GUI Lite software.
A list of some of the binaries and scripts supplied by Oracle Corporation to operate with/alongside Oracle databases and associated software appears on the Oracle executables web-page.
Other databases marketed by Oracle Corporation
By aquiring other technology in the database field, Oracle Corporation has taken over:
Using Oracle Database software
Users of Oracle databases may access the online documentation
, the Oracle Technology Network site, and the comp.databases.oracle Usenet
discussion group. The Oracle Technet
site offers downloads of full-featured evaluation software. Users can also check the Oracle FAQ
site before posting questions to forums, mailing lists, etc. They can also log on to http://asktom.oracle.com/ to post questions to and get answers from Tom Kyte
, a Vice-President of Oracle Corporation and the author of several Oracle books including Expert One-On-One Oracle
The Oracle RDBMS has had a reputation among novice users as difficult to install on Linux systems. Oracle Corporation has packaged recent versions for several popular Linux distributions in an attempt to minimize installation challenges beyond the level of technical expertise required to install a database server.
Users who have Oracle support contracts should turn to Oracle's MetaLink web site (password required). MetaLink 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.
Oracle Corporation also endorses certain practices and conventions as enhancing the use of its database products. These include:
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 variety of official (Oracle-sponsored)
and unofficial user groups has grown up of users and developers of Oracle databases. They include:
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 zSeries). The two companies have a relationship perhaps best described as "coopetition". 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 open-source relational database systems, particularly PostgreSQL, Firebird, and MySQL. Oracle acquired Innobase, supplier of the InnoDB codebase to MySQL, in part to compete better in the open source market. Database products developed on the basis of the open-source model generally cost significantly less to acquire than Oracle systems.
In 2007, competition with SAP AG occasioned litigation from Oracle Corporation.
Oracle Corporation offers term licensing for all Oracle products. It bases the list price for a term-license on a specific percentage of the perpetual license price. As of March 2006
, the "Enterprise Edition" of the Oracle database costs the most per machine-processor among Oracle database engines. Standard Edition comes cheaper: it can run on up to 4 processors but has fewer features than Enterprise Edition — it lacks proper parallelization, etc; but remains quite suitable for running medium-sized applications). Standard ONE edition sells even more cheaply, but remains limited to 2 CPUs. Standard Edition ONE sells on a per-seat basis with a 5-user minimum. Oracle Corporation usually sells the licenses with an extra 22% cost for support and upgrades (access to MetaLink - Oracle Corporation's support site) which customers need to renew annually.
Oracle Express Edition (Oracle XE), an addition to the Oracle database product family (beta
version released in 2005, production version released in February 2006), offers a free version of the Oracle RDBMS, but one limited to 4 GB of user data and to 1 GB of RAM. XE will use no more than one CPU and lacks an internal JVM
As computers running Oracle often have eight or more processors, the software price can rise into the hundreds of thousands of dollars. The total cost of ownership
exceeds this, as Oracle databases usually require experienced and trained database administrators
to do the set-up properly. Because of the product's large installed base and available training courses, Oracle specialists in some areas have become a more abundant resource than those for more exotic databases. Oracle frequently provides special training offers for database-administrators.
On Linux, Oracle's certified configurations
include mostly commercial Linux distributions
(RedHat Enterprise Linux 3 and 4, SuSE SLES8
and 9, Asianux
) which can cost in a range from a few hundred to a few thousand USD per year (depending on processor architecture and the support package purchased). One can avoid paying for those distros
by using free alternatives such as any Red Hat Enterprise Linux derivatives
(such as CentOS
or White Box Linux
). Oracle also runs stable on unsupported distributions.