Oracle 11g R2 introduced automatic memory management which takes care of dynamically expanding and shrinking the SGA and PGA based on instance needs. Only two parameters, memory_target and memory_max_target, need to be set. Memory_target sets the initial usable system memory size while memory_max_target defines the maximum amount of memory Oracle can use. For example, memory_max_target could be set to 500MB and memory_target to 350MB initially.