Explain SGA memory structures. SGA (System Global Area) is a dynamic memory area of an Oracle Server. In SGA,the allocation is done in granuels. The size of the SGA is dependent on SGA_MAX_SIZE parameter.
The memory structures contained by SGA are:-
Shared Pool -
this memory structure is divided into two sub-structures which are Library Cache and Data Dictionary Cache for storing recently used PL/SQL statements and the recent data definitions. The maximum size of the Shared Pool depends on the SHARED_POOL_SIZE parameter.
Database Buffer Cache -
This memory structure improves the performance while fetching or updating the recently used data as it stores the recently used datafiles. The size of this block is decided by DB_BLOCK_SIZE.
Redo Log Buffer -
This memory structure is used to store all the changes made to the database and it's primarily used for the data recovery purposes. The size of this block is decided by LOG_BUFFER.
Java Pool -
This memory structure is used when Java is installed on the Oracle server. Size that can be used is stored in parameter named JAVA_POOL_SIZE.
Large Pool -
This memory structure is used to reduce the burden of the Shared Pool, as the Session memory for the Shared Server, as the temporary storage for the I/O and for the backup and restore operations or RMAN. Parameter that stores the maximum size is LARGE_POOL_SIZE