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That statement is not correct.
Standby Redo Log must be archived before the redo data can be applied to the standby database.
That statement is not correct either. While Standby can use a process which is like generating archive, archive is really being transported from the Primary database.
If we put our standby database in noarchivelog mode, then standby database does not generate any archive. Because of this Redo data wont apply to the standby database. Right?
Yes. If you switch modes the standby becomes the primary and needs to be in archivelog mode.
Is this the reason why we put standby database in archivelog mode?
If you do a failover there are two main methods for recovery, RMAN and Flashback. You want your Standby database to be ready for use as a Primary, otherwise why have it? So you need to have it ready for anything including recovery.
I debated the archive question with somebody here last year. They claim the Standby produces Archive because such and such a process does this. I disagree. In Standby mode the database is not doing what a Primary mode database does. Those Oracle processes don't create new archive, they complete the transfer of archive from a Primary. The Sequence number was created on the Primary.
From Oracle document
"If all databases in a distributed database operate in ARCHIVELOG mode, you can perform coordinated distributed database recovery. However, if any database in a distributed database is in NOARCHIVELOG mode, recovery of a global distributed database (to make all databases consistent) is limited by the last full backup of any database operating in NOARCHIVELOG mode."
If you search this document
Data Guard Concepts and Administration 11g Release 2 (11.2) E10700-02
For "ARCHIVELOG" you get several hits.
If you search for "NOARCHIVELOG" you get none.
I suppose in theory you could run a Standby in "NOARCHIVELOG" but you gain nothing. If you ever have a switchover or failover you need to fix this ASAP. I see no reason to add that item to my checklist. It just an extra step and in the event of a failover one I could be very unhappy about.
Edited by: mseberg on Mar 15, 2013 1:25 PM