Re: Histograms Used to Select Best Index, or Only Between Index and FTS?

Hi Herman,

I generally don't like generalisations :)

IMHO, whether on not you generate histograms depends not so much on the environment (OLTP, DSS, Hybrid, whatever) but more so on whether the histograms offer any benefit. If they offer a benefit, use them if they don't, well don't.

In OLTP environments it's less likely they'll be useful as accesses are often through PKs, queries are smaller and bind variables are the norm.

In DSS the reverse is often the case.

However, if a column is *not* used in a where clause or the column has *even distribution* of values, then histograms are redundant (no matter the environment) And as well as the issues raised by JL, the gathering of these statistics is expensive.

So I always question the generating of histograms if there is no justification for doing so.

Richard
"Herman de Boer" <h.de.boer_at_itcg.nl> wrote in message news:ah6ao4$21k$1_at_news1.xs4all.nl...
> I should have been more specific.
>
> For DSS kind-of-databases, histograms on all columns
> for OLTP kind-oif databases: only if necessary. Agree with mr. Lewis.
>
> Kind Regards,
>
> Herman de Boer
> sr consultant
> IT Consultancy Group bv.
>
> Jonathan Lewis wrote:
>
> >
> >In general I advise quite strongly against having
> >histograms on all columns.
> >
>
Received on Thu Jul 18 2002 - 22:49:58 CDT