How to Check Oracle Instance Size
Instance Size=SGA_TARGET+PGA_AGGREGATE_TARGET.
Generally, Oracle MEMORY_TARGET parameter defines the total instance size.
Example, If MEMORY_TARGET is set to 10 GB, oracle will manage PGA + SGA within 10 GB
Show parameter memory_target;The MEMORY_MAX_TARGET parameter defines the maximum RAM that Oracle can use in case of heavy workloads. Example, if MEMORY_TARGET is set to 10 GB and MEMORY_MAX_TARGET is set to 20 GB, then during heavy workloads, Oracle instance can max take upto 20 GB RAM
show parameter memory_max_target;
The SGA_TARGET defines the SGA size and SGA_MAX_SIZE defines the maximum RAM SGA can take during heavy workloads.
show parameter sga_target; show parameter sga_max_size;
The PGA_AGGREGATE_TARGET defines the PGA size and PGA_AGGREGATE_LIMIT is set to (2 * PGA_AGGREGATE_TARGET).
show parameter pga_aggregate_target; show parameter pga_aggregate_limit; so, Instance Size=SGA_TARGET+PGA_AGGREGATE_TARGET
