The instance PGA memory is the collection of memory
allocations for all individual PGAs.
Beginning with Oracle Database 11g release 1 (11.1), you can let the database manage
the SGA memory and instance PGA memory completely. You designate only the total
memory size to be used by the instance, and Oracle Database dynamically exchanges
memory between the SGA and the instance PGA as needed to meet processing
demands. This capability is referred to as automatic memory management. In this
memory management mode, the database also dynamically tunes the sizes of the
individual SGA components and the sizes of the individual PGAs.
To have more direct control over the sizes of the SGA and instance PGA, use the
Memory Advisors page of Database Control to disable automatic memory
management and enable automatic shared memory management.