Simon Riggs <simon@2ndQuadrant.com> wrote:
> Normally, others come forward with the why? when? questions and it
> feels like there's a bit of groupthink going on here. This looks
> to me like its being approached like it was a feature, but it
> looks to me like a possible optimisation, so suggest we treat it
> that way.
This issue has come up a great many times over the years, and there
has been much discussion around it. The Wiki page is here:
http://wiki.postgresql.org/wiki/Index-only_scans
This currently references 11 threads on the topic. I'd bet that by
spending a couple hours at it I could quadruple that number of
threads. (I'd really rather not, though.)
The problem is that there are regular and fairly frequent complaints
on the list about queries which run slower than people expect
because the heap must be checked for visibility information when
matching index entries are found. It has become enough of a
conspicuous issue that a lot of people are interested in seeing if
something can be done about it. After much discussion, people are
trying to advance a plan to find an answer. I'm sure nobody
involved would ignore any suggestion on how it might be done better;
but at this point, I don't think it's fair to suggest that this is
not being pursued in response to a real problem, or that no serious
thought has been given to direction before people started moving.
-Kevin