比如:memory_target=100G,人为将alter system set sga_max_size=0 scope=spfile;那么数据库启动的时候sga_max_size会被设置为60G,也就是说sga运行期间不会超过60G。如果alter system set sga_max_size=90G scope=spfile;那么虽然数据库启动的时候sga分配成了60G,但是数据库运行期间会自动进行调整,但最高不超过90G
3、内存的查看及优化建议可以通过下面的三个语句进行查询
select * from v$memory_target_advice order by memory_size;
select * from v$pga_target_advice order by pga_target_for_estimate;
select * from v$sga_target_advice order by sga_size;