RE: Manual Standby as alternative to dataguard
- From: "Ric Van Dyke" <ric.van.dyke@xxxxxxxxxx>
- To: "Mathias Magnusson" <mathias.magnusson@xxxxxxxxx>, "sanjeev m" <sanjeevorcle@xxxxxxxxx>
- Date: Wed, 17 Jun 2009 06:31:22 -0500
I believe that the original problem is that the business folks are under
the impression that NOLOGGING does something that it doesn't.
The bottom line is that once an object has the NOLOGGING attribute
turned on, the only things that are not logged are actions that involve
the direct load code. So actions like a direct load via SQL Loader, or
an append insert. Other then that all actions are still logged even
with NOLOGGING turned on. So unless the business it doing a lot of
direct load type work, turning on FORCE LOGGING will likely not change
the way the application works at all. If it does do a lot of direct load
work then yes it will be affected. How much would need to be tested to
see, but yes the direct loads will slow down because they are now being
logged with FORCE LOGGING turned on. There are some other nuances to
having it off, like if you create it with it set to off then the objects
creation isn't logged, so the object would get created on the standby,
the apply process will need to skip any actions on that object if they
appear in the redo stream.
As to the argument about can you have a DR solution with FORCE LOGGING
off, I believe that it's creating a lot more work to have it turned off
then its worth. To make it work you have to be able to now manually do
the action that wasn't logged on the primary. Maybe thru RMAN backups,
or recreating the standby once and a while, or keeping track of all the
direct path operations and applying them just after activating the
standby but before you allow users to connect, any choice you pick is
not going to be easy and has a possibility for a mistake which leaves
you with inconsistent or flat out wrong data. If you're serious about
having a DR site then FORCE LOGGING turned on isn't optional. From a
technical point of view, yes the apply process will run just fine with
it on or off, but from a business and logical point of view it is very
important which setting FORCE LOGGING is set to.
-----------------------
Ric Van Dyke
Hotsos Enterprises
-----------------------
Hotsos Symposium
March 7 - 11, 2010
Be there.
________________________________
From: mathiasmag@xxxxxxxxx [mailto:mathiasmag@xxxxxxxxx] On Behalf Of
Mathias Magnusson
Sent: Wednesday, June 17, 2009 12:35 AM
To: sanjeev m
Cc: Jurijs Velikanovs; niall.litchfield@xxxxxxxxx; Ric Van Dyke;
oracle-l@xxxxxxxxxxxxx
Subject: Re: Manual Standby as alternative to dataguard
Let's go back to the actual problem. What do you do in the transactions
that causes this to be a problem? No-logging and forcing it only affects
a limited number of operations. Could it be that it is not clearly
understood by the business users when this actually would have an effect
on the performance?
And by the way, I believe posting data recieved in MetaLink of cound in
articles there is not allowed and could cause your support contract to
be revoked.
Mathias
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