RE: standbys and unrecoverable operations

  • From: "Bobak, Mark" <Mark.Bobak@xxxxxxxxxxxxxxx>
  • To: <Josh.Collier@xxxxxxxxxxxx>, <oracle-l@xxxxxxxxxxxxx>
  • Date: Tue, 15 Nov 2005 16:59:14 -0500

Josh,
 
I'm not a standby or DataGuard expert, but, think about what the
unrecoverable change # represents.  It's the SCN at which  the last
unrecoverable operation occurred on that datafile.  So, if the primary
is ahead of the standby, that means there are operations which have
occurred on the primary which did not propogate to the standby.  This is
a corruption waiting to happen.  If you activate the standby and a
datablock is accessed that was loaded unrecoverable on the primary,
you'll encounter an ORA-26040.
 
So, I assume (don't have a standby setup handy to confirm it) that the
default safe position is that they are equal, since, when you clone from
the primary to initially create the standby, they'd (presumably) be
equal.  At that point, the only way for them to get out of sync is if
you do an unrecoverable (aka nologging) load in the primary database.
 
Corrections welcome from those with actual DG and standby experience!
;-)
 
Hope that helps,
 
-Mark
 
PS  Note that in 9i (can't remember if it was 9.0.1 or 9.2.0
intorduction) you can do ALTER DATABASE FORCE_LOGGING=TRUE; and
everything will log, even if people try to do nologging loads.

________________________________

From: oracle-l-bounce@xxxxxxxxxxxxx
[mailto:oracle-l-bounce@xxxxxxxxxxxxx] On Behalf Of Josh Collier
Sent: Tuesday, November 15, 2005 4:52 PM
To: oracle-l@xxxxxxxxxxxxx
Subject: standbys and unrecoverable operations


Greetings,
 
The Oracle documentation says that if the unrecoverable_change# for a
datafile reported (v$datafile) by the primary is greater than that
reported by the standby then you will need to recover that datafile (by
copying it over from the primary) in order to avoid block corruption
errors if the standby is activated. 
 
Does this also hold if the unrecoverable_change# are identical? 
 
have a good day,
 
Josh C. 

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