Newsletters Archive - 2011

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  Using RMAN Incremental Backups to Roll Forward a Physical Standby Database (Oracle 10g) — (03-March-2011)

There are several scenarios that can occur in an Oracle Data Guard 
configuration which renders a physical standby database as either unusable or 
invalid. For example, an extended network failure can occur between the primary 
and standby machines which cause the standby database to fall significantly far 
behind the primary database. If the necessary archived redo log files needed to 
synchronize the physical standby database with the primary database are no 
longer available, log gap resolution will be unable to resolve the gap in the 
redo stream to catch up the standby.

Another popular scenario exists when a DML or DDL operation is performed on the 
primary database using the NOLOGGING or UNRECOVERABLE clause and the FORCE 
LOGGING database option is not enabled on the primary. If the FORCE LOGGING 
database option is not enabled, then Oracle will not log the entire operation 
in the redo log and thus, never send the modified data to the standby database 
for recovery. While this doesn't necessarily render the entire standby database 
as unusable, it does invalidate the standby for those tables affected and may 
require substantial DBA administrative activities to repair. Although you can 
specify the ALTER DATABASE FORCE LOGGING statement on the primary database to 
override the NOLOGGING clause and prevent this type of damage to occur in the 
future, this statement will not repair a standby database that has already been 
invalidated.

In each of the scenarios listed above, one solution would be to simply delete 
and formally re-create the physical standby database to enter it back into the 
Data Guard configuration. Depending on the size of the database, rebuilding the 
standby database could be an expensive operation as it would potentially 
involve a lot of time and resources making this a nonviable option.

The following guide presents a quick and efficient alternative to rebuilding a 
physical standby database in Oracle Database 10g Release 2 by using RMAN 
incremental backups to roll forward and resynchronize a physical standby 
database with the primary database. Using the RMAN BACKUP INCREMENTAL FROM SCN 
command, you can create an incremental backup on the primary database that 
starts at the standby database's current SCN, which can then be used to roll 
the standby database forward in time. 

Using RMAN Incremental Backups to Roll Forward a Physical Standby Database (Oracle 10g)

This guide will provide step-by-step recovery procedures which cover the 
following three scenarios:

o Physical Standby Database Lags Far Behind the Primary Database
o Physical Standby Database Has Nologging Changes On a Subset of Datafiles
o Physical Standby Database Has Widespread Nologging Changes 

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Jeffrey M. Hunter, OCP
Sr. Database Administrator
jhunter@idevelopment.info
http://www.idevelopment.info
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