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Home -> Community -> Mailing Lists -> Oracle-L -> RE: [Q] what differtent between logical standby database and physical standby DB?
Tanel
Guess, I am not understanding the word "construction" applied towards a
physical standby. Change vectors describe the changes at a lowest
granular level and KCB layer( I think..) has to apply the change vectors
directly to the data block buffer (of course, after reading the buffer
if not present in the cache etc..etc). I don't understand what need to
be constructed for the physical standby application. Are you refering to
redo block checksum verification or something along those lines ? You
also said parsing has to be done for the change vectors. Can you please
help me understand that too ?
I agree completely that lot more need to be done to reconstruct the SQL
in the case of logical standby.
Thanks a lot, Tanel!
Riyaj "Re-yas" Shamsudeen
Certified Oracle DBA
-----Original Message-----
From: oracle-l-bounce_at_freelists.org
[mailto:oracle-l-bounce_at_freelists.org] On Behalf Of Tanel Põder
Sent: Thursday, April 08, 2004 11:41 AM
To: oracle-l_at_freelists.org
Subject: Re: [Q] what differtent between logical standby database and
physical standby DB?
> Um, in the physical standby case, aren't the archivelogs simply =
> transferred to the standby server in their entirety? To the best of
> my = knowledge, physical standby doesn't do logmining, right?
It doesn't do logmining, but however, in both cases the changes have to be constructed from change vectors (and supplemental information) in redo records, the difference is that in logical apply scenario sql statements are constructed and passed to higher layer for sql processing, but in physical apply just datablocks are read and changes are applied to them directly (using kernel cache layer?).
The point I was trying to make was, that in both cases you have to parse the redo records to get the changes, that way you'd detect corruptions equally in both cases as well... yes SQL apply ignores some of the redo vectors in logs but on the other hand, it requires additional, supplemental records for its operations...
Tanel.
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