【分享】Oracle ADG 切换的几个场景和具体的切换步骤总结

计划内切换

-（1）检查主库

select switchover_status from v$database;

SWITCHOVER_STATUS

SESSIONS ACTIVE

if [ switchover_status = "SESSIONS ACTIVE" | switchover_status = "TO STANDBY" ];
then { go to next step }
else { cancel switchover and check database }

-（2）主库切为备库

alter database commit to switchover to physical standby with session shutdown;
shutdown immediate;
startup mount;

-（3）检查备库

select switchover_status from v$database;

SWITCHOVER_STATUS

TO PRIMARY

if [ switchover_status = "SESSIONS ACTIVE" | switchover_status = "TO PRIMARY" ];
then { go to next step }
else { cancel switchover and check database }

-（4）备库切为主库

alter database commit to switchover to PRIMARY with session shutdown;

-（5）原主库恢复日志应用

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

计划外切换

一、主备库日志没有缺口的场景

-（1）备库检查日志缺口

select thread#,low_sequence#,high_sequence# from v$archive_gap;
未选定行

-（2）备库停止日志接受并完成已收日志应用

alter database recover managed standby database cancel;
alter database recover managed standby database finish;

-（3）检查备库状态

select switchover_status from v$database;

SWITCHOVER_STATUS

TO PRIMARY

if [ switchover_status = "SESSIONS ACTIVE" | switchover_status = "TO PRIMARY" ];
then { go to next step }
else { cancel switchover and check database }

-（4）备库切为主库

alter database commit to switchover to PRIMARY with session shutdown;
alter database open;

二、主库可以打开到 mount 状态

-（1）将主库日志刷到备库

alter system flush redo to target_db_name;

-（2）备库停止日志接受并完成已收日志应用

alter database recover managed standby database cancel;
alter database recover managed standby database finish;

-（3）检查备库状态

select switchover_status from v$database;

SWITCHOVER_STATUS

TO PRIMARY

if [ switchover_status = "SESSIONS ACTIVE" | switchover_status = "TO PRIMARY" ];
then { go to next step }
else { cancel switchover and check database }

-（4）备库切为主库

alter database commit to switchover to PRIMARY with session shutdown;
alter database open;

三、主备库间日志缺口无法纠正。

-（1）强制激活备库

alter database activate physical standby database;
alter database open;