SQL> select switchover_status from v$database;
SWITCHOVER_STATUS
————————————————————
UNRESOLVABLE GAP
standby：
SQL> select switchover_status from v$database;
WITCHOVER_STATUS
————————————————————
not allowed
但是主备库之间是通的，也就是主库切换一个日志可以传输到备库上，但是没有应用
查看日志应用情况
SQL> SELECT SEQUENCE#,APPLIED FROM V$ARCHIVED_LOG ORDER BY SEQUENCE#;