导读
本文介绍Oracle 12c dataguard在维护方面的新变化
前提：主库备库的同步是正常的。

1、主库上查看archive Log list

SYS@cdb1> archive log list;
Database log mode              Archive Mode
Automatic archival             Enabled
Archive destination            /oradata/arch
Oldest online log sequence     39
Next log sequence to archive   41
Current log sequence           41
SYS@cdb1>

2、备库上查看archive log list

SYS@cdb1dg> archive log list;
Database log mode              Archive Mode
Automatic archival             Enabled
Archive destination            /oradata/arch
Oldest online log sequence     0
Next log sequence to archive   0
Current log sequence           0
SYS@cdb1dg>

主库和备库同步正常，可以正常切换，切换后，发现新的备库的archive Log list显示全部是0 。

3、解决方法

查看官方文档《Archive Log List Showing 0 At Standby, But Standby Is Completely In Sync With Primary! (文档 ID 2041137.1)》，根据官方文档提示，Oracle12c版本中的dataguard不需要用archive log list查看，要用下面的SQL来查看。

##主库查看：SYS@cdb1> select thread#, max(sequence#) 2  from v$archived_log a, v$database b3  where a.resetlogs_change# = b.resetlogs_change#4  group by thread# order by 1;THREAD# max(sequence#)
---------- --------------------------1                        130SYS@cdb1> select thread#, max(sequence#) 2  from v$archived_log a, v$database b3  where a.resetlogs_change# = b.resetlogs_change#4  and a.applied in ('YES','IN-MEMORY')5  group by thread# order by 1;THREAD# max(sequence#)
---------- ------------------------1                      130SYS@cdb1>

##备库查看：SYS@cdb1dg> select thread#, max(sequence#) 2  from v$archived_log a, v$database b3  where a.resetlogs_change# = b.resetlogs_change#4  group by thread# order by 1;THREAD# max(sequence#)
---------- --------------------------1                        130SYS@cdb1dg> select thread#, max(sequence#) 2  from v$archived_log a, v$database b3  where a.resetlogs_change# = b.resetlogs_change#4  and a.applied in ('YES','IN-MEMORY')5  group by thread# order by 1;THREAD# max(sequence#)
---------- ------------------------1                      130SYS@cdb1dg>

通过v$archive{d}_{l}og与v$database视图联合查询即可查看到主备库是否同步了。