Kjell

>>
>> Excellent analogy. If only the optimizer had enough statistics to tell
>> hay from needles...
>
> Perhaps an idea for future improvement? I guess it wuld require a
> different kind of index - some kind of hash buckets instead of b-trees?
>

No, what would be required, I think, is a histogram rather than a
single number for the selectivity of indexes. Postgres keeps
ten slot histograms for every field - not just index keys - and
members of their development group are arguing to increase the
number of slots to 100.

Cheers,

Ann