需关闭所有实例，再重新启动db服务生效：
10g:
alter system set "_gc_affinity_time"=0 scope=spfile;
alter system set "_gc_undo_affinity"=false scope=spfile;
11g:
alter system set "_gc_policy_time"=0 scope=spfile sid='*';
alter system set "_gc_undo_affinity"=false scope=spfile sid='*';
12c:
alter system set "_lm_drm_disable"=7 scope=both sid='*';