On Tue, 2010-05-04 at 07:13 -0400, Robert Haas wrote:
> 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.
It matches my experience. I think its a testament to the expertise of
our users as well to the hackers that have done so much to make that the
top of user's lists for change.
> 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.
The only way I see as genuine better rather than just a different mix of
trade-offs is to come up with ways where there are no conflicts. Hannu
came up with one, using filesystem snapshots, but we haven't had time to
implement that yet.
-- Simon Riggs www.2ndQuadrant.com