在oracle中

				--设定STATISTICS_LEVEL=TYPICAL才能监控PGA
				STATISTICS_LEVEL. Set this to TYPICAL (the default) or ALL; setting this
				parameter to BASIC turns off generation of PGA performance advice views.
				--查询
				SELECT round(PGA_TARGET_FOR_ESTIMATE/1024/1024) target_mb,
				   ESTD_PGA_CACHE_HIT_PERCENTAGE cache_hit_perc,
				   ESTD_OVERALLOC_COUNT
				FROM V$PGA_TARGET_ADVICE;