With Automatic Shared Memory Management, Oracle will use internal views and statistics to decide on the best way to allocate memory among the SGA components. The new process MMAN constantly monitors the workload of the database and adjusts the size of the individual memory components accordingly.

Note: In Oracle Database 10g, the database enables the Automatic PGA Memory Management feature by default. However, if you set the PGA_AGGREGATE_TARGET parameter to 0 or the WORKAREA_SIZE_POLICY parameter to MANUAL, Oracle doesn’t use Automatic PGA Memory Management.

As in previous version, you use the following parameters to set SGA component sizes:

In Oracle Database 10g, the value of the SHARED_POOL_SIZE parameter includes the internal overhead allocations for metadata such as the various data structures for sessions and processes.

You must, therefore, make sure to increase the size of the SHARED_POOL_SIZE parameter when you are upgrading to Oracle Database 10g. You can find the appropriate value by using the following query:

SGA_TARGET specifies the total size of all SGA components. If SGA_TARGET is specified, then the following memory pools are automatically sized:

o Buffer cache (DB_CACHE_SIZE)

o Shared pool (SHARED_POOL_SIZE)

o Large pool (LARGE_POOL_SIZE)

o Java pool (JAVA_POOL_SIZE)

o Streams pool (STREAMS_POOL_SIZE) in Release 2

If these automatically tuned memory pools are set to non-zero values, then those values are used as minimum levels by Automatic Shared Memory Management.

The following pools are not affected by Automatic Shared Memory Management:

o Log buffer

o Other buffer caches, such as KEEP, RECYCLE, and other block sizes

o Streams pool (in Release 1 only)

o Fixed SGA and other internal allocations

o The new Oracle Storage Management (OSM) buffer cache, which is    meant for the optional ASM instance The memory allocated to these pools    is deducted from the total available for SGA_TARGET when Automatic    Shared Memory Management computes the values of the automatically    tuned memory pools.

Note: If you dynamically set SGA_TARGET to zero, the size of the four auto-tuned shared memory components will remain at their present levels.

Note: The SGA_MAX_SIZE parameter sets an upper bound on the value of the SGA_TARGET parameter.

Note: In order to use Automatic Shared Memory Management, you should make sure that the initialization parameter STATISTICS_LEVEL is set to TYPICAL or ALL.

You can use the V$SGA_DYNAMIC_COMPONENTS view to see the values assigned to the auto-tuned components.

Whereas the V$PARAMETER will display the value you set to the auto-tuned SGA parameter, not the value assigned by the ASMM.

When you restart the instance, by using SPFILE Oracle will start with the values the auto-tuned memory parameters had before you shut down the instance.