Re: Proposed patch to make mergejoin cost estimation more symmetric

On Fri, 2007-12-07 at 09:48 -0500, Tom Lane wrote:
> Simon Riggs <simon@2ndquadrant.com> writes:
> > I do have a longer term issue that there is no information provided by
> > EXPLAIN to allow us to differentiate these two conditions.
>
> Sure there is: the new startup condition affects the estimated plan
> startup cost (only) and the existing termination condition affects the
> estimated total cost (only).

I think we all accept that you're the master here. The question is how
will we know to report problems to you? If we all get used to the idea
that sometimes the numbers vary, then we're in the situation where we
have to say to people "its magic". That destroys any feedback loop you
have for problem reporting and then you get out of touch with what is
happening on the ground.

It's a long term issue, so I have no complaints about what you've done,
its just something to think about. I've been exactly here before in one
of my past lives and I don't want to reinvent that particular wheel.

--
  Simon Riggs
  2ndQuadrant  http://www.2ndQuadrant.com