In the

database management system In computing, a database is an organized collection of data or a type of data store based on the use of a database management system (DBMS), the software that interacts with end users, applications, and the database itself to capture and an ...

s developed by the

Oracle Corporation Oracle Corporation is an American Multinational corporation, multinational computer technology company headquartered in Austin, Texas. Co-founded in 1977 in Santa Clara, California, by Larry Ellison, who remains executive chairman, Oracle was ...

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

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) 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 proprietary multi-model database management system produced and marketed by Oracle Corporation. It is a database commonly used for ru ...

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

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: 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 Corporation, ...

table Table may refer to: * Table (database), how the table data arrangement is used within the databases * Table (furniture), a piece of furniture with a flat surface and one or more legs * Table (information), a data arrangement with rows and column ...

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 In the Oracle RDBMS environment, redo logs comprise files in a proprietary format which log a history of all changes made to the database. Each redo log file consists of redo records. A redo record, also called a redo entry, holds a group of chang ...

* 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 proprietary multi-model database management system produced and marketed by Oracle Corporation. It is a database commonly used for ru ...

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

Granules

In the

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

, 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 In the Oracle RDBMS environment, redo logs comprise files in a proprietary format which log a history of all changes made to the database. Each redo log file consists of redo records. A redo record, also called a redo entry, holds a group of cha ...

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