RE: Common Oracle RDBMS Misconceptions - standby db?

With graceful standby failover (I demo'd it last year at OOW), you can switch back and forth, back and forth as many times as you want without recopying any database.

Basically, when you fail over to a standby, you shut down the primary, apply all the archived redologs to the standby, then copy all the online logs and the controlfile from the primary to the standby. People who use incremental checkpoints (DB_BLOCK_MAX_DIRTY_TARGET) must do a 'create controlfile reuse database <blah> noresetlogs' at this point. Other people don't have to.

Finally, you "recover database" to get the last one or two online logs and open the standby "noresetogs." The standby just picks up the chain of SCNs where the primary left off.

The old primary can be immediately pressed into service as a standby. Just generate a standby controlfile on the new primary, copy it into place on the old primary and start it up as a standby database.

You can go back and forth in this way as many times as you want, and one just picks up the chain of SCNs where the last one left off. You never get a divergence of changes.

I have talked to people who found this out, and looked like they were going to cry, thinking of the countless hours they had spent after every standby failover, recopying to the standby to get it rollong forward again.

In 9i, they have an "automated" graceful failover mechanism for standby database. I haven't taken a look at it yet. Probably it is a massive java-based GUI that instantly consumes 512Mb or RAM.

--
Jeremiah Wilton
http://www.speakeasy.net/~jwilton

On Tue, 26 Jun 2001, Koivu, Lisa wrote:



> OK.  I admit my knowledge on standby is minimal, having only read up on it,

> fiddled with it and used the idea sparingly for migrations.

>

> However, Jeremiah, I'm very curious.  You state that 'Must reinstantiate

> standby after failover by recopying' is a misconception. Yes, like many of

> the things you state below, the documentation does say that - once you open

> a standby db in r/w mode, it is no longer a valid standby after switching

> back to the primary.

>

> Can someone shed some light on why this is not true?  It seemed to make

> complete sense to me.  I can see how opening a database read only will work

> and not invalidate the standby, but r/w?


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Author: Jeremiah Wilton
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