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RE: DataGuard

From: Carel-Jan Engel <>
Date: Tue, 16 Jan 2007 08:41:17 +0100
Message-Id: <>


Read Expert Oracle Database Architecture, and/or Effective Oracle by design, both by Tom Kyte. And require your developers to read them too. Examine their knowledge after they told you they've read it. You're lucky. Your app hasn't been written yet.

Recently I got called in to a hosting center, to tune a database supporting an application that had to run 1.8 million transactions. Small transactions, roughly consisting of filling up a new table with 1.8 million rows. No big deal, I guessed/assumed. However, it turned out the Java guys screwed up the thing so badly that it couldn't complete more than 10.000 a day(!), producing over 60 GB of redo. They heavily used their version of temporary tables, shifting the data through the database many times. Everything was performed on a row by row basis, with tons of commits. This app appeared to be not optimized for minimum redo generation. Of course the bad performance was all to be blamed to the DBA's. Than it turned out that the owner of the development company was related to some director of the customer, and by definition their software was declared perfect. It was a snakepit full of politics. I gave up and withdrew.

Bottomline, to answer your question:

On Tue, 2007-01-16 at 14:20 +1300, Borrill, Christopher wrote:
> I have been following this discussion with interest, as I know our
> customer is concidering a solution similar to this for a new database
> and application we are about to write, but I have one question.
> How do you optimise an application for minimum redo generation?

By design!

Best regards,

Carel-Jan Engel

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

> ______________________________________________________________________
> From:
> [] On Behalf Of Carel-Jan Engel
> Sent: Tuesday, 16 January 2007 1:23 p.m.
> To:
> Cc:;
> Subject: RE: DataGuard
> Brandon,
> If the system is important for the business, they (the business)
> should provide enough (budget for enough) bandwidth. If they can
> afford the money for an extra server, with extra Oracle EE licenses,
> having a proper line with enough bw. shouldn't be a very difficult
> business case.
> If you follow the suggestion to use the local standby as a buffer for
> redo forwarding, be aware that an unknown amount of redo is not sent
> to the DR site at any given point in time. If at that point the
> disaster strikes, you will loose transactions. If the business is
> aware of that risk, and made the trade-off, fine! Let them confirm
> that to you in writing. Too often they are unaware, and the
> technicians get blamed in the event of a failover to the DR-site,
> loosing important transactions. Just because the techies were
> responible for the HA solution. Wrong. Management doesn't make
> housekeeping responsible for insuring the building either.
> Consider using hardware line cards to compress the redo traffic. Use
> QOS on the routers to prioritize the data sent on the portnumber you
> choose for redo transport. People might come up with the suggestion of
> using ssh tunneling with compression. IMHO: Too cumbersome for HA. You
> need an extra process, it will consume CPU, it can fail, needs
> monitoring, etc. James Morle used Cisco line cards at a DG site we set
> up and they got typically 4:1 compression. They were appr. $1000 each.
> No setup, no worries, no monitoring.
> Finally: is the application optimized for minimized redo generation?
> Best regards,
> Carel-Jan Engel
> ===
> If you think education is expensive, try ignorance. (Derek Bok)
> ===
> On Mon, 2007-01-15 at 16:48 -0700, Allen, Brandon wrote:
> > I'm not questioning Carel-Jan's recommendation at all - I think he
> > has more DG knowledge in his pinky than I'll ever have, but just
> > passing on a case where cascading setup might be
> > appropriate/necessary:
> > We have been struggling to get a standard (single standby) DG setup
> > working for the last few months because our network connection isn't
> > sufficient to keep up with the rate of our redo generation and when
> > the transfer of archived logs falls behind far enough, it eventually
> > freezes the production database. We're using ARCH to transfer the
> > logs and already tried upgrading to and setting the hidden
> > parameter _log_archive_callout='LOCAL_FIRST=true', but we still see
> > this behavior. Oracle Support's recommendation is to implement a
> > cascading standby where we ship the logs to a local standby first
> > and then go from the local to the remote so that the local standby
> > operates as a buffer to keep the slow network from halting our
> > primary. We are considering their recommendation, but going to try
> > everything else we can think of to avoid it first, which will
> > probably include upgrading to 10.2 because supposedly this problem
> > no longer occurs in 10g, but that's the same thing we were told
> > about with the local_first=true setting (Metalink 260040.1)
> > and we're not very confident based on our experience with that
> > config.
> > Of course another option that we're considering is increasing the
> > network bandwidth to the remote destination, but we would really
> > like to have dataguard configured such that it will absolutely never
> > impair production performance because even with the increased
> > bandwidth, there is always the possibility of WAN problems, someone
> > accidentally clogging the pipe with other large files, etc.
> > Carel-Jan, if you have any recommendations, we'd love to hear them!
> > Thanks,
> > Brandon
> >
> >
> > ____________________________________________________________________
> >
> > From:
> > [] On Behalf Of Carel-Jan Engel
> > Sent: Monday, January 15, 2007 4:12 PM
> >
> >
> > Stay away from cascaded redo transport as far as you can. You simply
> > don't want that in HA environments. As states:
> > '..Complexity is the enemy of availability...' (and I'd like to add:
> > '.. but the friend of consultancy...' J). Imagine a switchover with
> > cascaded transport. The whole redo transport stack has to be
> > reinvented. A star-configuration (primary points to both standbys)
> > is much easier to setup.
> >
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Received on Tue Jan 16 2007 - 01:41:17 CST

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