数据库服务的过程中，经常有客户因备库服务器宕机导致备库无法同步数据的问题，向我们咨询数据恢复服务，最近遇到有3例。
如果客户主库的归档日志没有删除，那么备库启动后会自动同步最近的日志文件，保持与主库的同步；很明显，上面客户归档日志随着备份完成而清理，导致备库无法自动恢复。
下面模拟该场景的故障恢复。
（一）测试环境主备
# 主、备库版本
SQL> select * from v$version;
BANNER
--------------------------------------------------------------------------------
Oracle Database 11g Enterprise Edition Release 11.2.0.4.0 - 64bit Production
PL/SQL Release 11.2.0.4.0 - Production
CORE 11.2.0.4.0 Production
TNS for Linux: Version 11.2.0.4.0 - Production
NLSRTL Version 11.2.0.4.0 - Production
#主库测试环境，产生较多归档日志
sys@ORCL> create table dgr tablespace tbs_baiyang as select * from all_objects;
sys@ORCL> alter system switch logfile;
#备库同步状态查询
SQL> select archived,max(sequence#),applied from v$archived_log group by archived,applied;
ARC MAX(SEQUENCE#) APPLIED
--- -------------- ---------
YES 81 IN-MEMORY
YES 80 YES
SQLL> select count(*) from dgr;
COUNT(*)
----------
84431
# 目前主备库同步正常（二）模拟故障环境
# 关闭备库
SQL> alter database recover managed standby database cancel;
SQL> shutdown immediate
# 主库执行大量更新操作，以产生大量归档日志
sys@ORCL> archive log list
Database log mode Archive Mode
Automatic archival Enabled
Archive destination /u01/app/oracle/oradata/orcl/archivelog
Oldest online log sequence 83
Next log sequence to archive 85
Current log sequence 85
sys@ORCL> insert into dgr select * from dgr;
84431 rows created.
sys@ORCL> insert into dgr select * from dgr;
168862 rows created.
sys@ORCL> insert into dgr select * from dgr;
337724 rows created.
sys@ORCL> update dgr set object_id = 11;
675448 rows updated.
sys@ORCL> commit;
Commit complete.
sys@ORCL> archive log list;
Database log mode Archive Mode
Automatic archival Enabled
Archive destination /u01/app/oracle/oradata/orcl/archivelog
Oldest online log sequence 93
Next log sequence to archive 95
Current log sequence 95
# 备份数据库
RMAN> backup database;
# 删除新生成归档日志文件
cd /u01/app/oracle/oradata/orcl/archivelog
$mkdir bak
$mv 1_9* bak/
# 打开备库
SQL> startup mount
SQL> select current_scn,database_role,open_mode from v$database;
CURRENT_SCN DATABASE_ROLE OPEN_MODE
----------- ---------------- --------------------
3730534 PHYSICAL STANDBY MOUNTED
# 开启日志应用报错
SQL> alter database recover managed standby database disconnect from session using current logfile;
alter database recover managed standby database disconnect from session using current logfile
*
ERROR at line 1:
ORA-01153: an incompatible media recovery is active
#查看下目前的日志应用状态，仍有新的归档日志传输到备库，但无法应用
SQL> select archived,max(sequence#),applied from v$archived_log group by archived,applied;
ARC MAX(SEQUENCE#) APPLIED
--- -------------- ---------
YES 97 NO
YES 89 YES
# 查看下是否有gap产生，少了5个日志文件，正式刚才删除的
SQL> select * from v$archive_gap;
THREAD# LOW_SEQUENCE# HIGH_SEQUENCE#
---------- ------------- --------------
1 90 94
# 以上就是模拟故障发生的步骤（三）恢复前的准备
以RMAN增量备份的方式恢复备库的过程中，需要重建备库的控制文件，势必需要了解当前备库的数据库文件、日志文件归属；如果主备文件目录保持一致，那么可以跳过这一步
# 日志目录
SQL> set linesize 300
SQL> col MEMBER for a60
SQL> select type,member from v$logfile;
TYPE MEMBER
------- ------------------------------------------------------------
ONLINE /u01/app/oracle/oradata/standby/redo03.log
ONLINE /u01/app/oracle/oradata/standby/redo02.log
ONLINE /u01/app/oracle/oradata/standby/redo01.log
STANDBY /u01/app/oracle/oradata/standby/standbylog/redo11.log
STANDBY /u01/app/oracle/oradata/standby/standbylog/redo12.log
STANDBY /u01/app/oracle/oradata/standby/standbylog/redo13.log
STANDBY /u01/app/oracle/oradata/standby/standbylog/redo14.log
# 数据文件目录
SQL> select name from v$datafile;
NAME
--------------------------------------------------------------------------------
/u01/app/oracle/oradata/standby/datafile/system01.dbf
/u01/app/oracle/oradata/standby/datafile/sysaux01.dbf
/u01/app/oracle/oradata/standby/datafile/undotbs01.dbf
/u01/app/oracle/oradata/standby/datafile/users01.dbf
/u01/app/oracle/oradata/standby/datafile/tbs_baiyang.dbf
/u01/app/oracle/oradata/standby/datafile/lxx2.dbf
# 查询当前备库的SCN
SQL> select current_scn,database_role,open_mode from v$database;
CURRENT_SCN DATABASE_ROLE OPEN_MODE
----------- ---------------- --------------------
3730534 PHYSICAL STANDBY MOUNTED
# 主库再进行一些更新操作
sys@ORCL> update dgr set object_id = 11;
675448 rows updated.
sys@ORCL> commit;
Commit complete.
（四）增量备份主库，及备份主库控制文件
# 增量备份
RMAN> run{
allocate channel c1 device type disk;
backup incremental from scn 3730534 database format '/oradata/ora_scn_%U.bak';
release channel c1;
}
RMAN> BACKUP CURRENT CONTROLFILE FOR STANDBY FORMAT '/oradata/ctl_20181213.bak';
# 将备份集传到备库
scp *.bak 172.16.8.123:/oradata/（五）恢复备库
# 首先使用增量备份恢复数据库
RMAN> catalog start with '/oradata/';
RMAN> recover database noredo;
……
channel ORA_DISK_1: restored backup piece 1
channel ORA_DISK_1: restore complete, elapsed time: 00:00:07
Finished recover at 13-DEC-18
# 关闭并重新备库至nomount状态，此时控制文件需要恢复（为什么）
SQL> startup nomount
# 使用主库控制文件备份恢复备库控制文件
RMAN> RESTORE STANDBY CONTROLFILE FROM '/oradata/ctl_20181213.bak';
Starting restore at 13-DEC-18
using channel ORA_DISK_1
channel ORA_DISK_1: restoring control file
channel ORA_DISK_1: restore complete, elapsed time: 00:00:01
output file name=/u01/app/oracle/oradata/standby/control01.ctl
output file name=/u01/app/oracle/fast_recovery_area/standby/control02.ctl
Finished restore at 13-DEC-18
#启动数据库到mount状态
SQL> alter database mount;（六）控制文件恢复后，数据和日志文件路径要是和备库现有不同，可以使用在线命令rename数据文件，重建日志文件，主要是standby 日志
……
ALTER DATABASE RENAME file '/u01/app/oracle/oradata/orcl/datafile/tbs_baiyang.dbf' to '/u01/app/oracle/oradata/standby/datafile/tbs_baiyang.dbf';
……
SQL> alter database add standby logfile group 24 '/u01/app/oracle/oradata/standby/standby24.log' size 50m;
……
SQL> alter database drop standby logfile group 14;
……（七）这时打开数据库、打开日志实时应用进程
SQL> alter database open;
SQL> alter database recover managed standby database disconnect from session using current logfile;
SQL> select archived,max(sequence#),applied from v$archived_log group by archived,applied;
ARC MAX(SEQUENCE#) APPLIED
--- -------------- ---------
YES 102 IN-MEMORY
YES 101 YES
SQL> select count(*) from dgr;
COUNT(*)
----------
675448
SQL> select count(*) from dgr where object_id=11 ;
COUNT(*)
----------
675448
为避免发生类似情况，（1）归档文件保留策略要尽可能的长，最好不要随着备份完成而删除（2）可以配置归档的备份策略，备份后可以删除归档，有需要从备份归档中还原
