RE: Data Guard

  • From: Carel-Jan Engel <cjpengel.dbalert@xxxxxxxxx>
  • To: mzito@xxxxxxxxxxx
  • Date: Sat, 08 Apr 2006 00:19:37 +0200

I don't understand the 'ease' of DNS-changing. Why hassling with yet
another system (The DNS server) if you can arrange the whole thing
locally on your database server? I use the multiple listener thing,
there's another method using service-registration: let only the services
representing the roles of your database be registered at the listener.
With both methods all of the failover stuff can be handled at DBA level:
no network guys or SA's needed to change the DNS, no flushing of the DNS
cache (or even rebooting?) of potentially tens or hundreds of machines
needed. The less people involved, the easier and smoother a failover
operation will work.

Best regards,

Carel-Jan Engel

If you think education is expensive, try ignorance. (Derek Bok)

On Fri, 2006-04-07 at 13:07 -0400, oracle-l-bounce@xxxxxxxxxxxxx wrote:

> I have no idea if this will work, but many naïve DNS caching systems cache 
> only the first label - that is, if has ip, it'll cache the 
> mapping from> .  If, however, is a CNAME to bar.baz, 
> and bar.baz has the IP, it might only cache the>bar.baz, not 
> the IP itself.  This allows you to change the IP of bar.baz without worrying 
> about the cache expiry.  
> Never having worked with either of these programs, I can't say if they'll 
> work, but I've used this trick before on a very large scale.
> Thanks,
> Matt
> -----Original Message-----
> From: oracle-l-bounce@xxxxxxxxxxxxx [mailto:oracle-l-bounce@xxxxxxxxxxxxx] On 
> Behalf Of JayMiller@xxxxxxxxxxxxxxxx
> Sent: Friday, April 07, 2006 11:48 AM
> To: oracle-l@xxxxxxxxxxxxx
> Subject: RE: Data Guard
> Just an added note if you go the DNS route (which is what we do).
> If you use Websphere or Microsoft Transaction Server (or probably most
> others) as a middle-tier connection manager then it will be necessary to 
> recycle the services after the DNS Name is switched since they "thoughtfully" 
> cache the ip address for you.  I remember the first time we did a 
> primary/standby switch after implementing the middle tier connection pooling 
> many years ago.  I still wake up screaming some nights :)
> Oh, if anyone knows a workaround for that I'd love to hear it.
> Basically all we ever got out of Oracle or IBM was "just recycle the services 
> to clear out the cached ip address".  It was supposed to be so easy to just 
> switch the DNS name...
> Jay Miller

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