Re: data guard questions

  • From: "Martin Bach" <development@xxxxxxxxxxxxxxxxx>
  • To: "Don Seiler" <don@xxxxxxxxx>,Brandon.Allen@xxxxxxxxxxx
  • Date: Thu, 17 Feb 2011 08:13:27 +0000

Excellent stuff! 

Going to order some new kit ;)

One more thing to note: cascaded standby is not supported if the primary is a 
RAC database. Even in 11.2. 

Martin Bach

Oracle Certified Master 10g

----- Reply message -----
From: "Don Seiler" <don@xxxxxxxxx>
Date: Thu, Feb 17, 2011 05:36
Subject: data guard questions
To: <Brandon.Allen@xxxxxxxxxxx>
Cc: "Sheehan, Jeremy" <JEREMY.SHEEHAN@xxxxxxxxxxxxxxxxx>, 
"oracle-l@xxxxxxxxxxxxx" <oracle-l@xxxxxxxxxxxxx>

Note that with cascading standbys you can only have 3 levels. Primary A ->
standby B -> standby C. You can have many other standby instances on the
same level as B, and many other instances on the same level as C. But you
can't have a C-level standby cascade any further.

I think prior to 11gR2, that "many other standby instances" was limited to
10, assuming that you are limited by the number of log_archive_dest_N
parameters. In 11gR2 this limit is raised to 31.

So, if you like theories, in theory you could have 10 standby on level B
each with 10 standby on level C for 100 total standby instances. But in
11gR2 you could have 31*31=961 standby instances, unless there is some new
cap on this that I'm not aware of (which is certainly possible).

But most practically you'd have 1 physical standby feeding from the primary,
and then a handful of others feeding off that one. I've only done this with
physical standby, but prior responses seem to indicate that physical to
logical works just fine.


On Wed, Feb 16, 2011 at 3:10 PM, Allen, Brandon

> No, real-time apply isn't another name for physical standby - it's just a
> configuration that enables the standby to apply redo as soon as it is
> received rather than waiting for an entire log file to be completed.  It can
> be implemented for both physical and logical standbys.  For more detail:
> Regards,
> Brandon
> -----Original Message-----
> From: Sheehan, Jeremy [mailto:JEREMY.SHEEHAN@xxxxxxxxxxxxxxxxx]
> Real time apply is another name for a physical standby (I think).
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Don Seiler

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