简介
SWITCHOVERS主要是在计划停机维护时用来降低DOWNTIME，如硬件维护、操作系统升级或是数据库rolling upgrade,
也可用来进行特殊情况下的数据库迁移。
SWITCHOVERS主要分为两个阶段，阶段1：主库转换为备库角色；阶段2：备库转换为主库角色
环境：
switchover 前
db_unique_name : ogg: primary
db_unique_name : tgg: physical standby
前提条件检查
1. standby log /redo log 在主备库都存在
select * from V$STANDBY_LOG;
select * from v$log
2. 确认主备处于归档模式
archive log list
3. 确认redo传输无错误、无GAP
SQL> SELECT STATUS, GAP_STATUS FROM V$ARCHIVE_DEST_STATUS WHERE DEST_ID = 2;
STATUS GAP_STATUS
--------- ------------------------
VALID NO GAP
4.确认主备库temprory file一样
SQL> select file_name from dba_temp_files;
FILE_NAME
--------------------------------------------------------------------------------
/u01/oradata/ogg/temp01.dbf
5.确认log_archive_dest_n参数设置正确
show parameter log_archive_dest_2
主库
SQL> show parameter log_archive_dest_2
NAME TYPE VALUE
------------------------------------ ----------- ------------------------------
log_archive_dest_2 string SERVICE=tgg LGWR SYNC VALID_FOR=(ONLINE_LOGFILES,PRIMARY_ROLE) DB_UNIQUE_NAME=tgg
备库
SQL> show parameter log_archive_dest_2
NAME TYPE VALUE
------------------------------------ ----------- ------------------------------
log_archive_dest_2 string service=ogg ASYNC valid_for=(ONLINE_LOGFILE,PRIMARY_ROLE) db_unique_name=ogg
开始SWITCHOVER
将主库ogg switchover to 备库
检查主库是否准备好进行角色转换
SQL> SELECT SWITCHOVER_STATUS FROM V$DATABASE;
SWITCHOVER_STATUS
--------------------
SESSIONS ACTIVE
SWITCHOVER_STATUS为SESSIONS ACTIVE，是因为还有有SESSION 连接到数据库，断开连接SESSION在查询如下
SQL> SELECT SWITCHOVER_STATUS FROM V$DATABASE;
SWITCHOVER_STATUS
--------------------
TO STANDBY
状态在SESSIONS ACTIVE 或者 TO STANDBY 都可以进行switchover操作
进行switchover
SQL> ALTER DATABASE COMMIT TO SWITCHOVER TO PRIMARY WITH SESSION SHUTDOWN;
Database altered.
将数据库重启到mount状态
SQL> shutdown immediate;
Database closed.
Database dismounted.
ORACLE instance shut down.
SQL> startup mount;
ORACLE instance started.
SQL> alter database open;
Database altered.
SQL> select database_role,db_unique_name,open_mode from v$database;
DATABASE_ROLE DB_UNIQUE_NAME OPEN_MODE
---------------- ------------------------------ --------------------
PRIMARY tgg READ WRITE
SQL> alter database open;
Database altered.
SQL> alter database recover managed standby database using current logfile disconnect from session;
Database altered.
SQL> select database_role,db_unique_name,open_mode from v$database;
DATABASE_ROLE DB_UNIQUE_NAME OPEN_MODE
---------------- ------------------------------ --------------------
PHYSICAL STANDBY ogg READ ONLY WITH APPLY
将备库tgg switchover to 主库
检查主库是否准备好进行角色转换
SQL> SELECT SWITCHOVER_STATUS FROM V$DATABASE;
SWITCHOVER_STATUS
--------------------
TO PRIMARY
进行switchover 操作
SQL> ALTER DATABASE COMMIT TO SWITCHOVER TO PRIMARY WITH SESSION SHUTDOWN;
Database altered.
开启新主库
SQL> alter database open;
Database altered.
检查角色转换结果
SQL> select database_role,db_unique_name,open_mode from v$database;
DATABASE_ROLE DB_UNIQUE_NAME OPEN_MODE
---------------- ------------------------------ --------------------
PRIMARY tgg READ WRITE
将新备库ogg 开启为read only --real time apply
SQL> alter database open;
Database altered.
SQL> alter database recover managed standby database using current logfile disconnect from session;
Database altered.
SQL> select database_role,db_unique_name,open_mode from v$database;
DATABASE_ROLE DB_UNIQUE_NAME OPEN_MODE
---------------- ------------------------------ --------------------
PHYSICAL STANDBY ogg READ ONLY WITH APPLY