Re: Learn Oracle in three days?

From: Daniel Morgan <dmorgan_at_exesolutions.com>
Date: Mon, 13 May 2002 18:13:21 GMT
Message-ID: <3CE00231.DCCA1822@exesolutions.com>

Pablo Sanchez wrote:

> "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

Thanks. I was hoping I wan't going to find another area of Oracle of which I was going to need to confess total ignorance. In this case it was only syntactic. Likely I can keep feeling good about the state of my knowledge until after lunch when I will get another email from a student. ;-)

Daniel Morgan Received on Mon May 13 2002 - 13:13:21 CDT