On Tue, May 4, 2010 at 4:37 AM, Simon Riggs <simon@2ndquadrant.com> wrote:
> option for them, especially for the stated reason. (My point about
> ndistinct: 99% of users have no idea that exists or when to use it, but
> it still exists as an option because it solves a known issue, just like
> this.)
Slightly OT, but funnily enough, when I was up in New York a couple of
weeks ago with Bruce and a couple of other folks, I started talking
with a DBA up there about his frustrations with PostgreSQL, and - I'm
not making this up - the first example he gave me of something he
wished he could do in PG to improve query planning was manually
override ndistinct estimates. He was pleased to here that we'll have
that in 9.0 and I was pleased to be able to tell him it was my patch.
If you'd asked me what the odds that someone picking a missing feature
would have come up with that one were, I'd have said a billion-to-one
against. But I'm not making this up.
To be honest, I am far from convinced that the existing behavior is a
good one and I'm in favor of modifying it or ripping it out altogether
if we can think of something better. But it has to really be better,
of course, not just trading one set of pain points for another.
...Robert