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Re: Learn Oracle in three days?

From: Pablo Sanchez <pablo_at_dev.null>
Date: Mon, 13 May 2002 10:53:03 -0600
Message-ID: <3cdfedd8$1_12@news.teranews.com>

"Daniel Morgan" <dmorgan_at_exesolutions.com> wrote in message news:3CDFEAF2.653BBB97_at_exesolutions.com...
> Pablo Sanchez wrote:
>
> > * Do you understand the concept of dense versus non-dense indexes?
> > * Do you understand why databases have a 'data' portion and a
'log'
> > portion?
> > * Do you understand why the need for checkpointing?
> > * Do you understand what happens on a DBMS failure and its
recovery
> > from the log perspective?
> > * Do you know how piggybacking off of an index can help you?
(also
> > known as a 'covered query')
> > * Do you know the I/O characteristics of the:
> > - log
> > - data
> >
> > (these kinda just came quickly)
>
>
> I was doing pretty well until I got to "covered query" or
"piggybacking".
> Not only have I not heard these phrases but they are not findable at
> tahiti.oracle.com, technet.oracle.com, etc.
>
> Could you please explain to what you refer.

Sure.

The idea comes from being able to satisfy a query from the index pages rather than the data pages. (That probably is enough for you to say, ah!) Because we have a higher density in indexes than data pages, a query that is satisfied by an index will outperform one that needs to be satisfied off of the data pages. Of course, 'covering your query' can be brittle because if you add another column to the query that is not in the index, your performance goes to 'mere mortal' status. <g>

--
Pablo Sanchez, High-Performance Database Engineering
mailto:pablo_at_hpdbe.com
http://www.hpdbe.com
Available for short-term and long-term contracts
Received on Mon May 13 2002 - 11:53:03 CDT

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