On Tue, May 10, 2011 at 3:25 AM, Robert Haas <robertmh...@gmail.com> wrote:

> So, what do we need in order to find our way to index-only scans?
>
> 1. The visibility map needs to be crash-safe.  The basic idea of
> index-only scans is that, instead of checking the heap to find out
> whether each tuple is visible, we first check the visibility map.  If

This topic has been discussed many times, yet I have never seen an
assessment that explains WHY we would want to do index-only scans.

This will be a complex addition to the codebase and one that could
introduce bugs into MVCC. It seems reasonable to look at what the
benefit of this would be, and what the use case/ benefit profile is
before we spend a long time adding this optimization.

I asked for this previously on earlier threads also.

-- 
 Simon Riggs                   http://www.2ndQuadrant.com/
 PostgreSQL Development, 24x7 Support, Training & Services

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