环境：Oracle 11.2.0.4 Data Guard

故障现象：
客户在备库告警日志中发现GAP sequence提示信息：

Mon Nov 21 09:53:29 2016
Media Recovery Waiting for thread 1 sequence 12034
Fetching gap sequence in thread 1, gap sequence 12034-12078
Mon Nov 21 09:55:20 2016
FAL[client]: Failed to request gap sequence
 GAP - thread 1 sequence 12034-12078
 DBID 3493955325 branch 881855745
FAL[client]: All defined FAL servers have been attempted.
------------------------------------------------------------
Check that the CONTROL_FILE_RECORD_KEEP_TIME initialization
parameter is defined to a value that's sufficiently large
enough to maintain adequate log switch information to resolve
archivelog gaps.
------------------------------------------------------------

修复过程：

• 1.查询备库SCN
• 2.确定主库是否添加数据文件
• 3.备库停止日志应用
• 4.主库增量备份并传输到备库上
• 5.备库上进行恢复
• 6.主库上创建standby controlfile文件并传输到备库
• 7.备库恢复控制文件
• 8.清空备库日志组
• 9.备库重设flashback
• 10.备库重新接收并应用日志
• 11.备库重新开启read only模式
• 12.验证修复是否成功
• Reference

查询备库当前SCN，如果人为造成控制文件、数据文件、数据文件头的SCN不一致，那么需要根据日志中gap的起始sequence#找出对应的SCN。可以查看文末reference中惜分飞的博客评论部分。

SQL> col CURRENT_SCN for 999999999999999999

SQL> SELECT CURRENT_SCN FROM V$DATABASE;

        CURRENT_SCN

-------------------

     11906842766974

select FILE#,name from v$datafile where CREATION_CHANGE#> =11906842766974;

确定主库在这个scn之后是否有添加数据文件，如果添加文件，需要手工在备库添加。本次没有遇到。

SQL> ALTER DATABASE RECOVER MANAGED STANDBY DATABASE CANCEL;

主库进行增量备份然后传输到备库上

RMAN> backup as compressed backupset INCREMENTAL from scn 11906842766974 database format '/backup/dumpfile/%u.bak';

$ scp *.bak 192.168.56.158:/oradata/rman/

RMAN> CATALOG START WITH '/oradata/rman/';

--注意如果此时库是read only则需要置换为mount后再进行recover操作；
RMAN> RECOVER DATABASE NOREDO;

主库上创建standby controlfile文件并传输到备库

RMAN> BACKUP CURRENT CONTROLFILE FOR STANDBY FORMAT '/home/oracle/std_ctl.bak';

[oracle@localhost ~]$ scp std_ctl.bak 192.168.56.158:/home/oracle/

备库关库，启动到nomount状态后恢复控制文件，最后启动到mount状态

RMAN> shutdown;

RMAN> STARTUP NOMOUNT;

RMAN> RESTORE STANDBY CONTROLFILE FROM '/home/oracle/std_ctl.bak';

RMAN> alter database mount;

本次DG中使用了standby log模式，不需要此步骤。

SQL> ALTER DATABASE CLEAR LOGFILE GROUP 1;

如果配置了physical standby redo log则不需该步骤；

如果没有采用standby log模式，有几组需要清空几组。

备库重设flashback（根据实际情况选做，这里DG环境备库本身就没开启，所以不用操作）

SQL> ALTER DATABASE FLASHBACK OFF;

SQL> ALTER DATABASE FLASHBACK ON;

备库重新接收并应用日志：

SQL> ALTER DATABASE RECOVER MANAGED STANDBY DATABASE using current logfile DISCONNECT FROM SESSION;

恢复过程备库最后的日志（最后需要出现Media Recovery Waiting for 字样）：

Mon Nov 21 17:17:05 2016

Managed Standby Recovery starting Real Time Apply

Parallel Media Recovery started with 32 slaves

Waiting for all non-current ORLs to be archived...

All non-current ORLs have been archived.

Completed: ALTER DATABASE RECOVER MANAGED STANDBY DATABASE using current logfile DISCONNECT FROM SESSION

Media Recovery Log /oradata/arch/1_12131_881855745.dbf

Mon Nov 21 17:18:59 2016

Media Recovery Log /oradata/arch/1_12132_881855745.dbf

Mon Nov 21 17:20:44 2016

Media Recovery Log /oradata/arch/1_12133_881855745.dbf

Mon Nov 21 17:21:02 2016

Media Recovery Log /oradata/arch/1_12134_881855745.dbf

Mon Nov 21 17:22:22 2016

Media Recovery Waiting for thread 1 sequence 12135 (in transit)

根据实际情况，备库重新开启read only模式，本次需求是需要备库read only状态应用日志（11g ADG特性）

SQL> alter database RECOVER MANAGED STANDBY DATABASE CANCEL;

SQL> alter database open;

SQL> ALTER DATABASE RECOVER MANAGED STANDBY DATABASE using current logfile DISCONNECT FROM SESSION;

12.1 对比最大sequence#
不一定准确（比如中间产生过gap，但是后期的归档日志正常传输，那么实际上虽然结果相同，但是还是有gap）

在主库中执行alter system switch logfile;

分别主备库中执行：select max(sequence#) from v$archived_log;

12.2 通过跟踪alert文件

主库告警：

tail -200f /oracle/diag/rdbms/shoucall/shoucall/trace/alert_shoucall.log

备库告警：

tail -200f /u01/app/oracle/diag/rdbms/shoucall_dg/shoucall/trace/alert_shoucall.log

：

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