On Thu, 2 May 2002, Patrick Welche wrote:
> On Wed, May 01, 2002 at 10:21:48PM -0400, Tom Lane wrote:
> > Patrick Welche <prlw1@newn.cam.ac.uk> writes:
> > > ... the select appears to take much longer to complete if the WHERE clause
> > > matches zero rows, than if it matches some rows.
> >
> > Doesn't make any sense to me. Are you sure the same plan is being
> > chosen in both cases? If so, could you post a complete example?
>
> Yes, same plan both cases. Thanks for the answer: as it doesn't make any
> sense to anyone, it must mean there is some corruption somewhere as a result
> of Monday morning's powercut => I'll look elsewhere.
Could it possibly be that, since it can't find any rows, it's fully
exhausting the indexes looking for the values it wants? I mean, a match
would presumably be found in the indexes before hitting the end, but a
non-match wouldn't. If the index is big enough, I could see a query
that returned no results taking longer than one which does.
--
+-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-+
| Shaun M. Thomas INN Database Administrator |
| Phone: (309) 743-0812 Fax : (309) 743-0830 |
| Email: sthomas@townnews.com AIM : trifthen |
| Web : www.townnews.com |
| |
| "Most of our lives are about proving something, either to |
| ourselves or to someone else." |
| -- Anonymous |
+-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-+
