Re: Availability during software/hardware upgrade.

Hi Howard-

Just wanted to add a few minor clarifications. Dataguard 3.0.2 for Oracle 8i fully supports "switchover" - i.e. graceful switching back and forth between primary and standby without ever needing to rebuild the standby. This has been available for 8i for some time now. For more information please see:

http://otn.oracle.com/docs/deploy/availability/pdf/A95293_01.pdf

... particularly the section on p. 3-34.

Also, in most cases minor patch differences between the two hosts are acceptable. The main concern is the same OS version and release. So using Dataguard to apply a patch to the standby and then "roll onto" it via graceful switchover is possible and not necessarily unsupported, though your mileage may vary.

As far as I know, Transparent Application Failover works just fine with a standby environment (i.e. you don't necessarily need RAC for TAF - you can have the "failover" TAF connection point to a standby database), though I have no direct experience with this.

Finally, as far as cost and complexity go, Dataguard certainly does add to the overall operational cost and upkeep. But for what it provides, the price is quite reasonable IMHO when compared with 3rd party remote disk mirroring solutions, and Dataguard definitely simplifies the care and feeding.

Regards,
Sean M

"Howard J. Rogers" wrote:
>
> Another flurry of useful replies, I see!
>
> Yes, what you ask for is possible, provided you have version 9i, and
> provided you implement something called Data Guard (ie, Standby Database on
> steroids).
>
> You have a requirement to switchover to Database 2, and then back again to
> Database 1: that's not possible with any version of Standby Database before
> 9i. You *could* "failover" to Database 2 in previous versions, but that
> caused Database 2 to receive a resetlogs, meaning it was in a new
> incarnation compared to Database 1, and meaning that you couldn't failover
> back to Database 1, until Database 1 had been completely blown away,
> re-cloned from Database 2, and the standby re-initialised.
>
> Havng said that, any and all versions of Standby, including Data Guard,
> require both Databases to be running on the same operating system, so it's
> not possible to use this mechanism to do a rolling upgrade from, say,
> Windows to Unix. And the doco. states that each O/S must be at the same
> patch release, so point upgrades of the same O/S are theoretically not
> possible either.
>
> The costs of Data Guard are considerable. Not only must you be running the
> Enterprise Edition, but to satisfy your requirement to lose no records,
> you'll have to be running in one of the three higher modes of protection
> which make LGWR do the transmission of redo from one Database to the other.
> And that has significant performance implications (nothing that some
> expensive kit won't fix!!).
>
> Another idea would be to use RAC (Real Application Clusters). You could
> have a two node RAC, take one of the nodes offline to patch it/upgrade
> it/whatever, and then bring it back into the cluster. Do the same on the
> other node, and you achieve truly non-zero downtime for the cluster as a
> whole. Again, however, you can't cluster a Windows box with a Unix one, so
> O/S changes are out of the question. Point release upgrades of the same O/S
> shouldn't necessarily be a problem, however.
>
> Also, I note you require no 'broken' transactions. Data Guard requires that
> you ask your users to get off the database nicely, so in theory you
> shouldn't break anything there. But RAC cannot failover DML (it can
> transparently failover selects, but not inserts, updates or deletes). So
> anyone connected to a RAC node that you cause to leave the cluster would
> lose any DML they were in the middle of.
>
> Anyway: that's two things for you to investigate: Data Guard and RAC. Both
> require the Enterprise Edition; both are expensive; both require good
> hardware; both are quite tricky maintenance prospects for the DBA.
>
> HTH
> Regards
> HJR
>
> "Andre Sluiter" <A.Sluiter_at_gesloten.nl> wrote in message
> news:3db50850.3320984_at_news.nl.uu.net...
> > Is it possible to change over from
> > hardware, OS version, Oracle version
> > without going off line ?
> >
> > I am thinking in the line of two (or more)
> > servers where server 1 is online, server 2 gets
> > upgraded, then a switch over from 1 to 2
> > server 1 get's upgraded and then a change back
> > to server 1.
> >
> > The switchover should be done without dataloss
> > or broken transactions.
> >
> > Is this possible ?
> > What is required for this ?
> > (If you can put a price on this please do,
> > or point me to a website or more info, thanks).
> >
> > Just checking if we should be looking into this.
> > (I have always claimed that if feasable this is
> > going to be to expensive for us, but have no
> > solid arguments).
> >
> >
> > Andre Sluiter
Received on Mon Oct 28 2002 - 21:05:08 CST