Re: index

"David BL" <davidbl_at_iinet.net.au> wrote in message news:f08bba46-7bd1-443e-97fd-fe07a9ec1a3f_at_25g2000hsx.googlegroups.com...
> On Jul 29, 10:45 am, "Brian Selzer" <br..._at_selzer-software.com> wrote:
> > "David BL" <davi..._at_iinet.net.au> wrote in message

> > > Physical duplication of data can be appropriate to increase read
> > > performance at the expense of write performance. Indeed any secondary
> > > index is a form of redundancy that hurts write performance.
> >
> > Boosting read performance can be accomplished just as well with a
> > covering
> > non-clustered index as with a clustered index.
>
> That is not always true. There could be an application involving a
> query that uses the non-clustered index and also needs *all* the
> additional data in the record. The additional seeks could mean the
> read performance doesn’t meet the requirements.

If the index is a /covering/ index, then there is no need for the additional read. Received on Tue Jul 29 2008 - 07:18:02 CEST