Re: About Access paths

On Sun, Mar 06, 2005 at 11:39:05PM +0200, Ioannis Theoharis wrote:
> > > As far as i can see, postgresql select a simple "INDEX SCAN using index"
> > > on table.
> >
> > That's because the index does not hold all the information. So INDEX
> > ONLY is impossible.
> >
>
> Thank you for your quick answer, but there is something a don't
> understand:
>
> the index holds all attributes' values (one index entry/one table entry).
> Right?
> given a query with only this attribute on SELECT clause, which is the
> missing information, that do not exist in index?

Visibility information. An index contains references to all rows in all
transactions. You need to go back to the table to work out if the row
is visible in your transaction.

Hope this helpsm
--
Martijn van Oosterhout <kleptog(at)svana(dot)org> http://svana.org/kleptog/
> Patent. n. Genius is 5% inspiration and 95% perspiration. A patent is a
> tool for doing 5% of the work and then sitting around waiting for someone
> else to do the other 95% so you can sue them.