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System Global Area (SGA) is a key component of the relational database management system (RDMS). Developed by Oracle Corporation, the SGA memory area is used by Oracle processes to hold shared database instance information critical to proper database functioning, including required incoming data and internal control data.
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Techopedia Explains System Global Area
Oracle uses initialization parameters to control the amount of allocated SGA memory. In Oracle Database 10g, the SGA is configured with the parameters "sga_target" and "sgs_max_size."
Oracle uses the automatic memory management feature to calculate and allocate memory to different SGA areas. Initialization parameters may also be used to manually allocate memory to individual SGA areas.
SGA components are as follows:
- Dictionary cache: Holds data dictionary table information, such as information regarding accounts, segments, data files, tables and privileges
- Redo log buffer: Includes information about committed transactions that have not yet been written to online redo log files
- Buffer_cache: Holds a copy of data blocks read from data files
- Shared pool: Holds a cache of parsed and commonly used Structured Query Language (SQL) statements
- Java pool: Parses Java statements
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