1、在备库中发现日志的归档日志不同步，内容如下：
MRP0: Background Media Recovery process shutdown (strac)
Managed Standby Recovery Canceled (strac)
Completed: alter database recover managed standby database cancel
Sun Mar 04 16:35:33 2018
Archived Log entry 96 added for thread 2 sequence 130 ID 0x971d6184 dest 1:
Sun Mar 04 16:35:33 2018
RFS[5]: Selected log 11 for thread 2 sequence 131 dbid -1759711868 branch 947273412
Sun Mar 04 16:35:34 2018
Archived Log entry 97 added for thread 2 sequence 131 ID 0x971d6184 dest 1:
RFS[5]: Selected log 11 for thread 2 sequence 132 dbid -1759711868 branch 947273412
Sun Mar 04 16:35:36 2018
Archived Log entry 98 added for thread 2 sequence 132 ID 0x971d6184 dest 1:
RFS[5]: Selected log 11 for thread 2 sequence 133 dbid -1759711868 branch 947273412
Sun Mar 04 16:39:32 2018
2、当在主库节点1中做切换时，备库中日志并不打印相关的日志进程信息，如果在主库节点2中做日志切换时，备库中是有打印日志的信息内容，内容见第一步中信息
3、通过第二步中的现象描述，可以先大概判断为是主库节点1中DG信息可能有问题导致归档日志无法同步过去
4、查询主库中配置归档位置配置的是否有错误信息，查询的结果如下：
SQL> select error from v$archive_dest where target=‘STANDBY‘
2 ;
ORA-12154: TNS:could not resolve the connect identifier specified
SQL> select error from v$archive_dest ;
ORA-12154: TNS:could not resolve the connect identifier specified
31 rows selected.
5、通过第4步中的结果，可以判断大概一个方向 ，可能是主库连接到备中监听有问题导致报错，先先TNS配置中查找原因
6、在主库节点1中tnsping 备库配置的服务名看是否报错，操作如下：
[oracle@rac1:/home/oracle]$tnsping strac
TNS Ping Utility for Linux: Version 11.2.0.4.0 - Production on 04-MAR-2018 16:57:32
Copyright (c) 1997, 2013, Oracle. All rights reserved.
Used parameter files:
Used TNSNAMES adapter to resolve the alias
Attempting to contact (DESCRIPTION = (ADDRESS_LIST = (ADDRESS = (PROTOCOL = TCP)(HOST = 192.168.1.103)(PORT = 1521))) (CONNECT_DATA = (SERVICE_NAME = strac)))rac =
TNS-12533: TNS:illegal ADDRESS parameters
7、此时在主库节点2中tnsping 备库服务名发现是可以正常解析过来的
[oracle@rac2:/home/oracle]$tnsping strac
TNS Ping Utility for Linux: Version 11.2.0.4.0 - Production on 04-MAR-2018 16:58:17
Copyright (c) 1997, 2013, Oracle. All rights reserved.
Used parameter files:
Used TNSNAMES adapter to resolve the alias
Attempting to contact (DESCRIPTION = (ADDRESS_LIST = (ADDRESS = (PROTOCOL = TCP)(HOST = 192.168.1.103)(PORT = 1521))) (CONNECT_DATA = (SERVICE_NAME = strac)))
OK (50 msec)
8、检查主库节点1中的TNS文件配置，经发现主库节点1中的TNS有很多的重复项，从而导致备库不能同步归档日志
9、从主库节点2中把TNS文件copy到主库节点1中，此时观察备库中的日志可以正常打印归档日志同步信息，详细内容如下：
Media Recovery Log /archlog/STRAC/archivelog/2018_03_04/o1_mf_1_175f9q9vwo0.arc
Media Recovery Log /archlog/STRAC/archivelog/2018_03_04/o1_mf_2_110f9q9qlco.arc
Media Recovery Waiting for thread 1 sequence 176
Fetching gap sequence in thread 1, gap sequence 176-176
Sun Mar 04 16:00:09 2018
RFS[6]: Opened log for thread 1 sequence 176 dbid -1759711868 branch 947273412
Archived Log entry 78 added for thread 1 sequence 176 rlc 947273412 ID 0x971d6184 dest 2:
Sun Mar 04 16:00:21 2018
Media Recovery Log /archlog/STRAC/archivelog/2018_03_04/o1_mf_1_176f9q9w9h5.arc
Media Recovery Log /archlog/STRAC/archivelog/2018_03_04/o1_mf_2_111f9q9qmng.arc
Media Recovery Waiting for thread 1 sequence 177
Fetching gap sequence in thread 1, gap sequence 177-177
Sun Mar 04 16:00:41 2018
RFS[6]: Opened log for thread 1 sequence 177 dbid -1759711868 branch 947273412
Archived Log entry 79 added for thread 1 sequence 177 rlc 947273412 ID 0x971d6184 dest 2:
Sun Mar 04 16:00:51 2018
Media Recovery Log /archlog/STRAC/archivelog/2018_03_04/o1_mf_1_177f9q9x92z.arc
Media Recovery Waiting for thread 1 sequence 178
Fetching gap sequence in thread 1, gap sequence 178-178
Sun Mar 04 16:00:51 2018
RFS[6]: Opened log for thread 1 sequence 178 dbid -1759711868 branch 947273412
Archived Log entry 80 added for thread 1 sequence 178 rlc 947273412 ID 0x971d6184 dest 2:
Sun Mar 04 16:01:01 2018
Media Recovery Log /archlog/STRAC/archivelog/2018_03_04/o1_mf_1_178f9q9xmc8.arc
Media Recovery Waiting for thread 1 sequence 179
Fetching gap sequence in thread 1, gap sequence 179-179
Sun Mar 04 16:01:01 2018
RFS[6]: Opened log for thread 1 sequence 179 dbid -1759711868 branch 947273412
Archived Log entry 81 added for thread 1 sequence 179 rlc 947273412 ID 0x971d6184 dest 2:
Sun Mar 04 16:01:11 2018
Media Recovery Log /archlog/STRAC/archivelog/2018_03_04/o1_mf_1_179f9q9xxgx.arc
Media Recovery Log /archlog/STRAC/archivelog/2018_03_04/o1_mf_2_112f9q9qmwy.arc
Media Recovery Log /archlog/STRAC/archivelog/2018_03_04/o1_mf_2_113f9q9qmyd.arc
Media Recovery Log /archlog/STRAC/archivelog/2018_03_04/o1_mf_2_114f9q9qncn.arc
Media Recovery Waiting for thread 1 sequence 180
Fetching gap sequence in thread 1, gap sequence 180-180
Sun Mar 04 16:01:11 2018
RFS[6]: Opened log for thread 1 sequence 180 dbid -1759711868 branch 947273412
Archived Log entry 82 added for thread 1 sequence 180 rlc 947273412 ID 0x971d6184 dest 2:
Media Recovery Log /archlog/STRAC/archivelog/2018_03_04/o1_mf_1_180f9q9y7sn.arc
Media Recovery Log /archlog/STRAC/archivelog/2018_03_04/o1_mf_2_115f9q9qncr.arc
Media Recovery Waiting for thread 1 sequence 181
总结说明：
1、当发现备库中有日志不同步时，可以先从判断配置DG配置项着手，然后通过v$archive_dest 表可以查看当前的归档状态是否正常，本环境中由于原来的DG环境是正常的，后面出现的问题，可以判断初步搭建环境是Ok的。
2、通过v$archive_dest 查询当前的DG的归档日志信息，如果里面有报错信息，可以提供一个大概的参考范围，方便我们定位问题
原文地址：http://blog.51cto.com/xiaocao13140/2082846
