Automatic Shared Memory Management (ASMM)

The commonly tuned System Global Area (SGA) components are the database buffer cache, the shared pool, the large pool, and the Java pool. The ASMM enables Oracle Database 10g to automatically determine the appropriate values of these components within the limits of the total SGA.

In previous versions of Oracle Database, the Oracle server allotted the memory for the fixed SGA and other internal allocations. Under-sizing can lead to poor performance and out-of-memory errors (ORA-4031), while over-sizing can waste memory. In Oracle Database 10g, the DBA can set the total amount of SGA memory available to an instance using the sga_target initialization parameter. Oracle database will automatically distribute this memory among various sub-components to ensure the most effective memory utilization.

The sga_target parameter includes all SGA memory, including automatically sized components, manually sized components, and internal allocations during the database startup. The default value is 0, and ASMM is disabled for this value.

The initialization parameters for the SGA components, db_cache_size (default pool only), shared_pool_size, large_pool_size, and java_pool_size, are still valid in the Oracle Database 10g and are referred to as auto-tuned SGA parameters.