Re: planner/optimizer question

I know you will shoot me down, but...

Why is there an entry in the index for a row if the row is not valid? 
Wouldn't it be better for the index entry validity to track the row validity. 
If a particular data value for a query (join, where etc.) can be satisfied 
by the index entry itself this would be a big performance gain.

Cheers,
Gary.

On 28 Apr 2004 at 0:27, Tom Lane wrote:

> brad-pgperf@duttonbros.com writes:
> > ... Wouldn't the most efficient plan be to scan the index regardless
> > of crm_id because the only columns needed are in the index?
> 
> No.  People coming from other databases often have the misconception
> that queries can be answered by looking only at an index.  That is never
> true in Postgres because row validity info is only stored in the table;
> so we must always visit the table entry to make sure the row is still
> valid/visible for the current query.
> 
> Accordingly, columns added to the index that aren't constrained by the
> WHERE clause are not very useful ...
> 
> 			regards, tom lane
> 
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