alter database recover managed standby database disconnect from session;

--应用备库的归档日志

alter database recover managed standby database using current logfile disconnect from session;

--应用备库的standby redo日志，关机的时候不会归档，重启后实例恢复redo日志会进入数据库

以上两种方式的切换可以通过alter database recover managed standby database cancel来实现

验证：主库备库执行select open_mode,protection_mode,protection_level from v$database查看结果

      备库执行SELECT SEQUENCE#, FIRST_TIME, NEXT_TIME, APPLIED FROM V$ARCHIVED_LOG ORDER BY SEQUENCE#;查看archive log的applied是否yes

DATAGURAD直接startup后，create/alter user和create table都报错如下，alter system是可以的，毕竟是修改参数

ORA-16000: database open for read-only access

一般启动的步骤如下

startup  nomount;

alter database mount standby database;

alter database open read only;

alter database recover managed standby database disconnect from session;

alter database recover managed standby database cancel;

alter database recover managed standby database disconnect from session;

其实可以直接如下(也是最好的一种，毕竟遇到很多归档需要recover时是不能直接open的)

startup mount（默认就是standby database了，因为是restore主库的standby controlfile）

alter database open read only;

alter database recover managed standby database disconnect from session;

alter database recover managed standby database cancel;

alter database recover managed standby database disconnect from session;

其实更可以直接如下

Startup(备库startup后默认就是read only，可以查询select open_mode from v$database，遇到很多归档日志需要recover的时候时会报错需要更多的恢复然后提示只能到mount状态)

alter database recover managed standby database disconnect from session;

alter database recover managed standby database cancel;

alter database recover managed standby database disconnect from session;