Re: Oracle Myths- Tablespace placement answered by Oracle

Alan wrote:

> I have Jonathan's book, and supoprt his rules comlpetely. I also add the
> following:
>
> The only reliable benchmark is how it runs on your system.
>
> Anyway, I posted the tablespace question on Metalink, and here is the
> repsonse:
>
> "Queries are not serial in that one does not read all the relevant index
> block and then start retrieving rows. But, it's not full concurrent either,
> in that it reads 1 index block at a time then we fetch the relevant data
> blocks. i.e. read one index block, retrieve the relevant rows, repeat, etc.
> The only true parallelism would be parallel query.
>
> Even without concurrency in the strictest sense it is still beneficial to
> put the indexes and data on different disks. The above info relates to one
> query. There is nothing to stop multiple queries against the same rows and
> indexes from processing concurrently.
>
> So yes, you can get performance benefit by splitting the data and indexes
> onto different disks."
>
> "Niall Litchfield" <n-litchfield_at_audit-commission.gov.uk> wrote in message
> news:3ce4be26$0$230$ed9e5944_at_reading.news.pipex.net...
> > "Alan" <alanshein_at_erols.com> wrote in message
> > news:ac1304$m75sv$1_at_ID-114862.news.dfncis.de...
> > > Well, I read through the archived messages, and discovered that either
> > half
> > > the Oracle experts don't know what they're talking about, or that half
> the
> > > Oracle experts know what they are talking about. The other half aren't
> > > talking. Anyway, I posted the question to Metalink, so we'll see what
> the
> > > consensus of the Oracle cube-dwellers is. Too bad there's no SQL
> standard
> > > related to this problem- if there was we could count on a definitive
> > answer,
> > > or at least one from Joe Celko.
> >
> > Of course you can ignore this if I don't know what I am talking about! but
> > Jonathan's book has the following lesson drawn from the Cautionary Tale
> > which I consider to be some of the best advice to be found in any Oracle
> > book anywhere.
> >
> > 1. You only know what you have discovered so far
> > 2. What worked last time might not work next time
> > 3. Different isn't necessarily wrong.
> >
> > At least some of the rules I've referred to above as Myths have or had
> some
> > basis in fact. Others of them notably the buffer cache myth have some
> merit
> > but don't actually say what they are widely considered to say. I'm
> > considering working some of these (say the top 5) into a presentation, but
> > it will be interesting to see what comes out of your tar and Mark's offer
> to
> > raise with the devs. (plus I'm hoping to have 9i2 to play with soon
> > bandwidth permitting)
> >
> >
> > --
> > Niall Litchfield
> > Oracle DBA
> > Audit Commission UK
> > *****************************************
> > Please include version and platform
> > and SQL where applicable
> > It makes life easier and increases the
> > likelihood of a good answer
> >
> > ******************************************
> >
> >

Thanks. But I feel like I am trying to walk across quick sand.

Has Oracle support bought into the myth or is it still "generally speaking" good advice?

I am not convinced that striping across multiple disks is the same thing as placing them physically onto separate disks. The former doesn't necessarily balance the I/O. It may just give the illusion by obscuring the location.

Daniel Morgan Received on Fri May 17 2002 - 11:10:05 CDT