I cannot stop myself to share a few great views which provide excellent information

V$SGA :
We can get information about the system global area (SGA)

V$SGA_DYNAMIC_COMPONENTS:
Can get information about the dynamic SGA components. This summy provides details based on all completed SGA resize operations since instance startup. All sizes are expressed in bytes.

V$SGAINFO:

Can get information about the SGA, including the sizes of different SGA components, the granule size, and free memory.

V$SGASTAT

We can get detailed information on the system global area (SGA).

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