standbys and unrecoverable operations 2005-11-15 - By Bobak, Mark
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 (See ORA-26040.ora-code.com).
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@(protected)
[mailto:oracle-l-bounce@(protected)] On Behalf Of Josh Collier
Sent: Tuesday, November 15, 2005 4:52 PM
To: oracle-l@(protected)
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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<DIV dir=ltr align=left><SPAN class=375435221-15112005><FONT face=Arial
color=#0000ff size=2>Josh,</FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=375435221-15112005><FONT face=Arial
color=#0000ff size=2></FONT></SPAN> </DIV>
<DIV dir=ltr align=left><SPAN class=375435221-15112005><FONT face=Arial
color=#0000ff size=2>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 (See ORA-26040.ora-code.com).</FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=375435221-15112005><FONT face=Arial
color=#0000ff size=2></FONT></SPAN> </DIV>
<DIV dir=ltr align=left><SPAN class=375435221-15112005><FONT face=Arial
color=#0000ff size=2>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.</FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=375435221-15112005><FONT face=Arial
color=#0000ff size=2></FONT></SPAN> </DIV>
<DIV dir=ltr align=left><SPAN class=375435221-15112005><FONT face=Arial
color=#0000ff size=2>Corrections welcome from those with actual DG and standby
experience! ;-)</FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=375435221-15112005><FONT face=Arial
color=#0000ff size=2></FONT></SPAN> </DIV>
<DIV dir=ltr align=left><SPAN class=375435221-15112005><FONT face=Arial
color=#0000ff size=2>Hope that helps,</FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=375435221-15112005><FONT face=Arial
color=#0000ff size=2></FONT></SPAN> </DIV>
<DIV dir=ltr align=left><SPAN class=375435221-15112005><FONT face=Arial
color=#0000ff size=2>-Mark</FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=375435221-15112005><FONT face=Arial
color=#0000ff size=2></FONT></SPAN> </DIV>
<DIV dir=ltr align=left><SPAN class=375435221-15112005><FONT face=Arial
color=#0000ff size=2>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.</FONT></SPAN></DIV><BR>
<DIV class=OutlookMessageHeader lang=en-us dir=ltr align=left>
<HR tabIndex=-1>
<FONT face=Tahoma size=2><B>From:</B> oracle-l-bounce@(protected)
[mailto:oracle-l-bounce@(protected)] <B>On Behalf Of </B>Josh
Collier<BR><B>Sent:</B> Tuesday, November 15, 2005 4:52 PM<BR><B>To:</B>
oracle-l@(protected)<BR><B>Subject:</B> standbys and unrecoverable
operations<BR></FONT><BR></DIV>
<DIV></DIV>
<DIV><SPAN class=513324921-15112005><FONT face=Arial
size=2>Greetings,</FONT></SPAN></DIV>
<DIV><SPAN class=513324921-15112005><FONT face=Arial
size=2></FONT></SPAN> </DIV>
<DIV><SPAN class=513324921-15112005><FONT face=Arial size=2>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.
</FONT></SPAN></DIV>
<DIV><SPAN class=513324921-15112005><FONT face=Arial
size=2></FONT></SPAN> </DIV>
<DIV><SPAN class=513324921-15112005><FONT face=Arial size=2>Does this also hold
if the unrecoverable_change# are identical? </FONT></SPAN></DIV>
<DIV><SPAN class=513324921-15112005><FONT face=Arial
size=2></FONT></SPAN> </DIV>
<DIV><SPAN class=513324921-15112005><FONT face=Arial size=2>have a good
day,</FONT></SPAN></DIV>
<DIV><SPAN class=513324921-15112005><FONT face=Arial
size=2></FONT></SPAN> </DIV>
<DIV><SPAN class=513324921-15112005><FONT face=Arial size=2>Josh C.
</FONT></SPAN></DIV></BODY></HTML>
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