System Global Area
shared memory structure that is created by Oracle databases at instance startup
In the database management systems developed by the Oracle Corporation, the System Global Area (SGA) forms the part of the system memory (RAM) shared by all the processes belonging to a single Oracle database 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: holds information about data dictionary tables, 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 Java statements.
large pool: including the User Global Area (UGA))
stream pool:this is remote connectivity for the database.
Configuration
From Oracle Database 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.
Begin with the source’s own compact description: “System Global Area” is shared memory structure that is created by Oracle databases at instance startup. The dossier treats that line as a proposition to test through System, Global and Area, not as a finished interpretation.
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The phrase “shared memory structure that is created by Oracle databases at instance startup” supplies a clear boundary for inquiry. It also exposes the unanswered questions: who defined that boundary, when it became stable and which sources sit outside it.
The citation trail is more important than the brevity of the summary: it shows where individual claims can be examined in context. The source revision retrieved here is dated May 18, 2026. The linked authority identifier is Q997772. None of the 0 selected statements returned an explicit reference.
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This entry incorporates text from “System Global Area” on English Wikipedia. Contributors are listed in the page history. Text is available under the Creative Commons Attribution-ShareAlike 4.0 License. Selected authority identifiers and statements are retrieved from Wikidata under CC0; their references and qualifiers remain part of the verification path.