Re: estimating # of distinct values

Dne 19.1.2011 20:46, Tom Lane napsal(a):
> Robert Haas <robertmhaas(at)gmail(dot)com> writes:
>> ... I guess I'm just saying I'd think really, really hard
>> before abandoning the idea of periodic sampling. You have to get an
>> awful lot of benefit out of those cross-column stats to make it worth
>> paying a run-time cost for them.
>
> I've been trying to not discourage Tomas from blue-sky speculation,
> but I have to say I agree with Robert that the chance of any usable
> result from this approach is very very small. Feel free to do some
> experimentation to prove us wrong --- but don't put a lot of effort
> into it before that.
>
> regards, tom lane

Discourage? Not really - I have not expected this to be a simple thing
to implement. And yes, it might turn out to be a dead end eventually.

OTOH the approach "it seems really expensive so let's not try to build
it" is a certain dead end, so I'm not going to surrender due to such
speculations (althouh those are valid concerns and I'll have to address
them in the future).

regards
Tomas