Dynamic SGA provides external controls for increasing and decreasing Oracle's use of physical memory. Together with the dynamic buffer cache, shared pool, and large pool, dynamic SGA allows the following:
The SGA can grow in response to a database administrator statement, up to an operating system specified maximum and the SGA_MAX_SIZE specification.
The SGA can shrink in response to a database administrator statement, to an Oracle prescribed minimum, usually an operating system preferred limit.
Both the buffer cache and the SGA pools can grow and shrink at runtime according to some internal, Oracle-managed policy.