what is the difference between pga aggregate limit and pga_aggregate_target?
Before Oracle 12c, PGA_AGGREGATE_TARGET is the most useful parameter to control PGA memory allocated to work areas. However PGA_AGGREGATE_TARGET is a soft target and not a hard limit. ... PGA_AGGREGATE_LIMIT is a new parameter introduced in 12c. It put a hard limit instead of a soft limit on the PGA memory usage.