System Global Area

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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[edit]

In general, the SGA consists of the following:

  • dictionary cache: information about data dictionary tables, such as information about account, datafile, segment, extent, table and privileges
  • redo log buffer: containing information about committed transactions that the database has not yet written to online redo log files
  • the buffer_cache or "database buffer cache": holds copies of data blocks read from datafiles[1]
  • shared pool, the cache of parsed commonly used SQL statements, and also the data-dictionary cache containing tables, views and triggers
  • Java pool, for parsing Java statements.
  • large pool (including the User Global Area (UGA))

Configuration[edit]

From Oracle Database version 10g, Automatic Memory Management (AMM) allows simplified and dynamic configuration of the SGA.[2]

See also[edit]

Further reading[edit]

References[edit]

  1. ^ "Memory Architecture" in Oracle Database Concepts 11g Release 1 (11.1)
  2. ^ Burleson, Donald K., ed. (2003). Oracle Database 10g New Features: Oracle 10g Reference for Advanced Tuning & Administration. Oracle In-Focus. Rampant TechPress. p. 22. ISBN 9780974071602. Retrieved 2012-11-22. "Oracle Database 10g [...] has Automatic Memory Management (AMM) in the form of the [...] parameter [...] sga_target, which [...] automates the allocation of RAM between the data buffers, shared pool, and log buffers."