In the

database management system In computing, a database is an organized collection of data stored and accessed electronically. Small databases can be stored on a file system, while large databases are hosted on computer clusters or cloud storage. The design of databases span ...

s developed by the

Oracle Corporation Oracle Corporation is an American multinational computer technology corporation headquartered in Austin, Texas. In 2020, Oracle was the third-largest software company in the world by revenue and market capitalization. The company sells da ...

, the System Global Area (SGA) forms the part of the system memory (

RAM Ram, ram, or RAM may refer to: Animals * A male sheep * Ram cichlid, a freshwater tropical fish People * Ram (given name) * Ram (surname) * Ram (director) (Ramsubramaniam), an Indian Tamil film director * RAM (musician) (born 1974), Dutch * ...

) shared by all the processes belonging to a single

Oracle database Oracle Database (commonly referred to as Oracle DBMS, Oracle Autonomous Database, or simply as Oracle) is a multi-model database management system produced and marketed by Oracle Corporation. It is a database commonly used for running online t ...

instance. The SGA contains all information necessary for the instance operation.

Components

In general, the SGA consists of the following: * buffer cache: holds copies of data blocks read from datafiles * dictionary

cache Cache, caching, or caché may refer to: Places United States * Cache, Idaho, an unincorporated community * Cache, Illinois, an unincorporated community * Cache, Oklahoma, a city in Comanche County * Cache, Utah, Cache County, Utah * Cache County ...

: holds information about

data dictionary A data dictionary, or metadata repository, as defined in the ''IBM Dictionary of Computing'', is a "centralized repository of information about data such as meaning, relationships to other data, origin, usage, and format". ''Oracle'' defines it ...

table Table may refer to: * Table (furniture), a piece of furniture with a flat surface and one or more legs * Table (landform), a flat area of land * Table (information), a data arrangement with rows and columns * Table (database), how the table data ...

s, such as information about account, datafile, segment, extent, table and privileges * redo log buffer: contains information about database transactions, both committed and uncommitted, in preparation for writing to online redo log files * shared pool: holds the dictionary or row cache, the library cache, cursor definitions and shared SQL. * Java pool: holds information for parsing

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statements. * large pool: including the User Global Area (UGA)) * stream pool:this is remote connectivity for the database.

Configuration

From

Oracle Database Oracle Database (commonly referred to as Oracle DBMS, Oracle Autonomous Database, or simply as Oracle) is a multi-model database management system produced and marketed by Oracle Corporation. It is a database commonly used for running online t ...

version 10g, Automatic Memory Management (AMM) allows simplified and dynamic configuration of the SGA.

Granules

In the Oracle DBMS, the Oracle server allocates the system global area (SGA) in granule units at the time of instance startup. During the startup, each component acquires as many granules as it requires. The SGA can be said to consist of linked granules. The granule size depends on the database version and sometimes on the operating system. In Oracle 9i and earlier, it is 4 MB if the SGA size is less than 128 MB, and 16 MB otherwise. For later releases, it is typically 4 MB if the SGA size is less than 1 GB, and 16 MB otherwise. There must be at least 3 granules in the SGA: one for the Database Buffer Cache, one for the Shared Pool Area and one for the

Redo Log Undo is an interaction technique which is implemented in many computer programs. It erases the last change done to the document, reverting it to an older state. In some more advanced programs, such as graphic processing, undo will negate the las ...

Buffer. It is possible to retrieve information about the current granule size at any time by querying the dynamic view V$SGAINFO.

References

Oracle software {{database-software-stub.

Components

Configuration

Granules

See also

Further reading

References