> I hit an interestinhg paper on n_distinct calculation:
>
> http://www.pittsburgh.intel-research.net/people/gibbons/papers/distinct-values-chapter.pdf
>
> the PCSA algorithm described there requires O(1) calculation per
> value. Page 22 describes what to do with updates streams.
>
> This I think (disclaimer: I know little about PG internals) means that
> the n_distinct estimation can be done during vacuum time (it would
> play well with the visibility map addon).
>
> What do You think?
ok, if You think that calculating a has function of every data field
for each insert or delete is prohibitive, just say so and don`t bother
reading the paper :]
Greetings
Marcin