如何利用闪回数据库特性恢复failover后的dataguar

如何利用闪回数据库特性恢复failover后的dataguard环境？

11g dataguard standby 切成主库，测试完成后恢复为原standby 环境


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概述：
11204 单机对单机实施dg，因局方要求需要（读写模式）打开standby ；而这时原生产环境不能有任何影响动，依然对外服务；
采用的思路是：standby 直接failover 为primary db；这时原有dg关系被破坏，互不影响；


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思路概要：
1.确认主库归档日志存放空间是否足够？（需考虑归档保留删除策略？）；关闭主库到备库的日志传输
2.备库确认是否开启flashback database，以及闪回日志存放空间是否充足？
3.备库failover to primary （切换前确认是否日志延迟传输？手工注册）
4.业务测试
5.恢复failover 备库
6.确认dg 环境恢复是否正常（日志自动传输和应用？）？



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具体实施步骤：

------主库defer 日志传输
alter system set log_archive_dest_2=defer;

---enable 日志传输：
alter system set log_archive_dest_2=enable；

-----备库(mount)配置 flashback database：
STANDBY DATABASE: Stop redo apply, configure flashback retention,
start flashback database, open the database and start redo apply (Is active DG).

---检查备库是否启用flashback database:
select flashback_on from v$database;


注意这里需要确认下备库打开模式： mount？readonly with apply？
在11g 环境下备库可能启用了 ADG 特性 备库日志处于实时应用，数据库模式为 readonly with apply
这时需要重启数据库到mount状态修改flashback database 模式；


如果备库处于mount 状态，可以先取消日志apply ，直接打开闪回数据库特性；


---取消备库日志应用：
ALTER DATABASE RECOVER MANAGED STANDBY DATABASE CANCEL;


---需要配置一下两个参数来打开flashback database 特性：
ALTER SYSTEM SET db_recover_file_dest='/lixora/lixora/lixora/';
ALTER SYSTEM SET db_recover_file_dest_size=100G;

ALTER SYSTEM SET DB_FLASHBACK_RETENTION_TARGET=240; ---4hours
ALTER DATABASE FLASHBACK ON;

--手工创建还原点（该步骤没有测试过）：
Creating Restore point in Physical Standby：
CREATE RESTORE POINT before_damage GUARANTEE FLASHBACK DATABASE


-------备库failover to primary db 应急切换步骤：
（注：模拟主库由于故障无法正常switchover，需要执行failover，强制备库->pridb并接管业务）

1.备库：
由于是failover，所以理解主库这时候已经无法正常使用，只需备库切换至pridb

【前提主库还是可用的：可选】查询没有应用的日志：
SELECT THREAD#, LOW_SEQUENCE#, HIGH_SEQUENCE# FROM V$ARCHIVE_GAP;

select distinct thread#,max(sequence#) over(partition by thread#) a from v$archived_log;
该语句取得当前数据库各线程已归档文件最大序号，如果primary 与standby 最大序号不相同，
必须将多出的序号对应的归档文件复制到待转换的standby服务器。


Cp过来并register
ALTER DATABASE REGISTER PHYSICAL LOGFILE 'filespec1'

停止应用恢复模式
alter database recover managed standby database finish;
or
ALTER DATABASE RECOVER MANAGED STANDBY DATABASE FINISH FORCE;

转换standbydb为primary db
alter database commit to switchover to primary;


重启数据库，恢复正常业务
alter database open；


数据库角色查看：
select open_mode,database_role from v$database;
OPEN_MODE DATABASE_ROLE
---------- ----------------
OPEN PRIMARY


------恢复failover 的备库：
C. Using SQL*PLUS
Step 1 Determine the Standby Became Primary SCN.
Step 2 Flashback the Failed Primary Database.
Step 3 Convert to physical standby database.
Step 4 Restart Redo Transport.
Step 5 Start Redo Apply.


Step 1 Determine the SCN at which the old standby database became the primary database.
SQL> SELECT TO_CHAR(STANDBY_BECAME_PRIMARY_SCN) FROM V$DATABASE;


Step 2 Flashback the Failed Primary Database to SCN standby_became_primary_scn.
SQL> SHUTDOWN IMMEDIATE;
SQL> startup mount
SQL> FLASHBACK DATABASE TO SCN ;

Step 3 Convert the database to a physical standby database and Restart database in mount stage.
SQL> ALTER DATABASE CONVERT TO PHYSICAL STANDBY;
SQL> SHUTDOWN IMMEDIATE;
SQL> STARTUP MOUNT;


Step 4 Restart Redo Transport to the New Physical Standby Database.
1. If you have not set the remote archive destination on current primary then set remote archive destination:
SQL>ALTER SYSTEM SET LOG_ARCHIVE_DEST_2 = 'SERVICE=lixora VALID_FOR=(ONLINE_LOGFILES,PRIMARY_ROLE) DB_UNIQUE_NAME=lixora' SCOPE=BOTH;

2. Enable the destination
SQL>ALTER SYSTEM SET LOG_ARCHIVE_DEST_STATE_2=ENABLE;

3. Perform a log switch to ensure that standby database begins receiving redo data from the new primary database
SQL> ALTER SYSTEM SWITCH LOGFILE;
SQL> SELECT DEST_ID, STATUS, ERROR FROM V$ARCHIVE_DEST WHERE DEST_ID=2;


--确认日志是否都apply了？
select applied from v$archived_log;

select message from v$dataguard_status;


Step 5 Start Redo Apply.
SQL> ALTER DATABASE RECOVER MANAGED STANDBY DATABASE DISCONNECT FROM SESSION;
Please see also fallowing docu:


TIPS：
Oracle? Data Guard Concepts and Administration
11g Release 2 (11.2)
13.2 Converting a Failed Primary Into a Standby Database Using Flashback Database