开启备库恢复：
数据库启动时，先启动备库，在启动主库
数据库关闭时，先关闭主库，在关闭备库
SYS@ prodstd>recover managed standbydatabase disconnect from session; --只要启动备库就使能recover功能
SYS@ prod>select max(sequence#) from v$archived_log;服务器、数据库环境：
主库服务器hostname：prod1 备库服务器hostname：prod2
主库数据库SID：prod 备库数据库SID：prodstd切换备库前准备，查看主库备库状态：
SYS@ prod>select tablespace_name,file_name from dba_data_files;
SYS@ prod>select max(sequence#) from v$archived_log; --对比主备库日志，同步才能做下一步
SYS@ prod>select username,sid from v$session where username is not null; --切换时要停库，最好没有其他session链接
SYS@ prod>select name,open_mode,database_role,protection_mode,switchover_status from v$database;
NAME OPEN_MODE DATABASE_ROLE PROTECTION_MODE SWITCHOVER_STATUS
--------- -------------------- ------------------------------------ --------------------
PROD READ WRITE PRIMARY MAXIMUM PERFORMANCE TO STANDBY
SYS@ prodstd>select name,database_role,protection_mode,switchover_status from v$database;
NAME DATABASE_ROLE PROTECTION_MODE SWITCHOVER_STATUS
--------- ---------------- ----------------------------------------
PROD PHYSICAL STANDBY MAXIMUM PERFORMANCE NOT ALLOWED主备切换步骤：
主库操作：
SYS@ prod>alter database commit to switchover to standby; 没有其他用户登录
或
SYS@ prod>alter database commit to switchover to standby with session shutdown; 有用户登录，强制切换
SYS@ prod>shutdown --彻底关闭数据库SYS@ prod>startup mount --先启动到mount下
SYS@ prod>select name,open_mode,database_role,protection_mode,switchover_status from v$database;
NAME OPEN_MODE DATABASE_ROLE PROTECTION_MODE SWITCHOVER_STATUS
--------- -------------------- ------------------------------------ --------------------
PROD MOUNTED PHYSICAL STANDBY MAXIMUM PERFORMANCE TO PRIMARY
备库操作：SYS@ prodstd>select name,open_mode,database_role,protection_mode,switchover_status from v$database;
NAME OPEN_MODE DATABASE_ROLE PROTECTION_MODE SWITCHOVER_STATUS
--------- -------------------- ---------------- -------------------- --------------------
PROD READ ONLY PHYSICAL STANDBY MAXIMUM PERFORMANCE TO PRIMARY
SYS@ prodstd>alter database commit to switchover to primary; --备库为主库
SYS@ prodstd>select name,open_mode,database_role,protection_mode,switchover_status from v$database;
NAME OPEN_MODE DATABASE_ROLE PROTECTION_MODE SWITCHOVER_STATUS
--------- -------------------- ---------------- -------------------- --------------------
PROD MOUNTED PRIMARY MAXIMUM PERFORMANCE NOT ALLOWED
SYS@ prodstd>alter database open; --开启备库，此时备库已经成为主库主库操作：
SYS@ prod>alter database open;SYS@ prod>select name,database_role,protection_mode,switchover_status from v$database;
NAME DATABASE_ROLE PROTECTION_MODE SWITCHOVER_STATUS
--------- ---------------- -------------------- --------------------
PROD PHYSICAL STANDBY MAXIMUM PERFORMANCE RECOVERY NEEDED
SYS@ prod>recover managed standby database disconnect from session; --原主库（当前备库）开启恢复。
SYS@ prod>select name,database_role,protection_mode,switchover_status from v$database;
NAME DATABASE_ROLE PROTECTION_MODE SWITCHOVER_STATUS
--------- ---------------- -------------------- --------------------
PROD PHYSICAL STANDBY MAXIMUM PERFORMANCE NOT ALLOWED主备切换成功
