在介绍ORA-20079前我们先简单介绍一下resync catalog：
Using the RESYNC CATALOG Command
Any structural changes to the database cause the control file and recovery catalog to become “out of synch.” The catalog will be synchronized automatically when a BACKUP or COPY command is issued with a connection to the catalog. However, this synchronization can cause a [B]delay[/B] in the backup operation.
在RMAN中使用catalog时，会使用同步命令来保证catalog与目标数据库的controlfile的內容一致。
通常，如果我们一直使用catalog来做backup or restore的话就不需要手工的做同步，因为我们发出的backup or restore命令完成后会自动同步catalog和controlfile中的內容，只有我们有时候用catalog，而有某些时候又不用catalog来做backup or restore的时候才需要发出 resync catalog的命令来手工做同步。Oracle同步catalog时，会先建立个snapshot controlfile并且比较这个文件和catalog，完成比较后，oracle根据这个snapshot controlfile来同步catalog，并使它们保持一致。
公司的某套生产环境库为11.2.0.3RAC+DG（AIX），在备库上作备份。一次发现备份失败，报错如下：
RMAN> RMAN>
ORA-20079: full resync from primary database is not done
doing automatic resync from primary
resyncing from database with DB_UNIQUE_NAME EGMMDB
RMAN-00571: ===========================================================
RMAN-00569: =============== ERROR MESSAGE STACK FOLLOWS ===============
RMAN-00571: ===========================================================
RMAN-03002: failure of configure command at 03/25/2014 04:52:42
RMAN-03014: implicit resync of recovery catalog failed
RMAN-03009: failure of partial resync command on default channel at 03/25/2014 04:52:42
ORA-17629: Cannot connect to the remote database server
ORA-17627: ORA-00942: table or view does not exist
在mos上找到了几个处理方案，可供参考
After new files are added to primary, rman fails at Standby with ORA-20079: Full Resync From Primary Database Is Not Done (Doc ID 1604302.1)
RMAN-06613: Connect identifier for DB_UNIQUE_NAME not configured (Doc ID 1598653.1)