DG由于网络原因或者bug原因经常不同步，有时隔得时间久了，就会丢失归档日志，或者长时间的归档恢复较慢，有一种可以基于scn的方式来恢复DG库，使用基于scn的增量备份来恢复standby库可以节省大量时间，或者进行dg异常的重新同步。
1，查询主库和备库的scn，redo号等信息，选取合适的scn号进行主库的备份
--查询DG端最低的scn，以下查询结果应该相同 select to_char(current_scn) scn from v$database; select min(fhscn) from x$kcvfh; select distinct to_char(checkpoint_change#) from v$datafile_header order by 1; --以归档日志查询相关scn select THREAD#,min(sequence#) from v$archived_log where applied='NO' group by THREAD#; select THREAD#,max(sequence#) from v$archived_log where applied='NO' group by THREAD#; SELECT thread#,SEQUENCE#,to_char(FIRST_CHANGE#) fc,to_char(NEXT_CHANGE#) nc FROM v$archived_log WHERE SEQUENCE# = 32995 ORDER BY 1,2;
2，主库端基于scn的增量备份
RMAN> BACKUP INCREMENTAL FROM SCNDATABASE FORMAT '/tmp/ForStandby_%U' tag 'FORSTANDBY'--or backup device type disk incremental from scn 11125946510 database format'/home/oracle/db_incre%U.bbk'; --orrun {allocate channel t1 type 'sbt_tape' parms 'ENV=(NB_ORA_CLIENT=bossb1)';allocate channel t2 type 'sbt_tape' parms 'ENV=(NB_ORA_CLIENT=bossb1)';allocate channel t3 type 'sbt_tape' parms 'ENV=(NB_ORA_CLIENT=bossb1)';allocate channel t4 type 'sbt_tape' parms 'ENV=(NB_ORA_CLIENT=bossb1)';allocate channel t5 type 'sbt_tape' parms 'ENV=(NB_ORA_CLIENT=bossb1)';allocate channel t6 type 'sbt_tape' parms 'ENV=(NB_ORA_CLIENT=bossb1)';allocate channel t7 type 'sbt_tape' parms 'ENV=(NB_ORA_CLIENT=bossb1)';allocate channel t8 type 'sbt_tape' parms 'ENV=(NB_ORA_CLIENT=bossb1)';backup incremental from scn 12844051683640 database format 'forstandby_%u' tag 'forstandby';backup current controlfile for standby format 'forstandbyctrl.bck' tag 'forstandby_cnt'; release channel t1; release channel t2; release channel t3; release channel t4; release channel t5; release channel t6; release channel t7; release channel t8;} ALTER DATABASE CREATE standby controlfile AS '/home/oracle/standby.ctl';
3，传输文件到dg端，rman catalog start with
4，恢复控制文件，恢复数据库
RMAN>restore controlfile from'/data/oracle/backup/restore/standby.ctl'; --mount databaseRMAN> RECOVER DATABASE NOREDO;
5，启动同步进程，检查同步状态等。