SGA

SGA:
The SGA is Oracle's structural memory area that facilitates the transfer of data and information between clients and the Oracle database.

sql>SHOW SGA



Total System Global Area 168783792 bytes
Fixed Size 737200 bytes
Variable Size 134217728 bytes
Database Buffers 33554432 bytes
Redo Buffers 274432 bytes

Total System Global Area : - Total in bytes of all the sub-divisions that makes up the SGA.

Fixed Size: Fixed size contains general information about the state of the database and the instance, which the background processes need to access. This does not store user data. Usually this area is less than 100k in size.

Variable Size: This part is influenced by the following init.ora parameters. shared_pool_size large_pool_size java_pool_size Database Buffers:

This holds data blocks copies that are read from datafiles and can be calculated by using following formula. size = db_block_buffers * block size Redo Buffers: This is another buffer in the SGA that holds information about changes made to the database.

Approximating size calculation of the SGA

Oracle 9i: To approximate size of the SGA (Shared Global Area), use following formula: db_cache_size + db_keep_cache_size + db_recycle_cache_size + db_nk_cache_size + shared_pool_size + large_pool_size + java_pool_size + log_buffers + 1mb