| From: | marcin mank <marcin(dot)mank(at)gmail(dot)com> |
|---|---|
| To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
| Cc: | kouber(at)saparev(dot)com, pgsql-performance(at)postgresql(dot)org |
| Subject: | Re: LIMIT confuses the planner |
| Date: | 2009-03-23 00:56:50 |
| Message-ID: | b1b9fac60903221756ifd951a3o4d8cb25854f2ade9@mail.gmail.com |
| Views: | Raw Message | Whole Thread | Download mbox | Resend email |
| Thread: | |
| Lists: | pgsql-performance |
> 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
| From | Date | Subject | |
|---|---|---|---|
| Next Message | Tom Lane | 2009-03-23 02:18:57 | Re: LIMIT confuses the planner |
| Previous Message | marcin mank | 2009-03-23 00:12:14 | Re: LIMIT confuses the planner |