Oracle

From RemObjects Software

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Oracle is a relational database management system (RDBMS) produced by the Oracle Corporation. The Oracle database server allows you to store and retrieve data in a multiuser environment.

Basic concepts

• An Oracle Server allows clients and administrators to connect to one or more instances. A Database instance is composed of the SGA (the System Global Area) and various background processes that Oracle uses to serve the database. The System Global Area (SGA) is a memory area that contains data shared between all database users such as the buffer cache and a shared pool of SQL statements. The memory and processes of an instance manage the associated database's data efficiently and serve the one or multiple users of the database.

• The RAM memory associated with the server is known as PGA (or the Program Global Area). The PGA is a memory buffer that is allocated for each individual database session and it contains session specific information such as SQL statement data or buffers used for sorting. The value specifies the total memory allocated by all sessions, and changes will take effect as new sessions are started.

• Oracle database conventions refer to defined groups of ownership (generally associated with a "username") as schemas. Each user owns a single schema. Schema objects can be created and manipulated with SQL and include: tables, views, and other types of data objects.

• The Oracle RDBMS stores data logically in the form of tablespaces and physically in the form of data files.

• The parse tree and the execution plan for every unique SQL statement are cached in the library cache. If multiple applications issue the same SQL statement, this area can be accessed by each to reduce the amount of memory needed and to reduce the processing time used for parsing and execution planning.

• Oracle stores information about the logical and physical structure of the database (user information, integrity constraints defined for tables in the database, names and data types of all columns in database tables, information on space allocated and used for schema objects) in the data-dictionary cache.

Supported platforms

• Linux x86, x86_64, zSeries, Itanium, POWER
• Microsoft Windows x86, NT (x64), NT (x64 Itanium)
• Solaris x86, AMD64/EM64T, SPARC (64-бит)
• AIX5L
• HP-UX PA-RISC, Itanium
• HP Tru64 UNIX
• HP OpenVMS Alpha
• IBM z/OS
• Mac OS X Server

See Also

• Data Abstract Drivers
• Connect to Oracle Server (AnyDAC)