| From: | Surafel Temesgen <surafel3000(at)gmail(dot)com> |
|---|---|
| To: | Tomas Vondra <tomas(dot)vondra(at)2ndquadrant(dot)com> |
| Cc: | Robert Haas <robertmhaas(at)gmail(dot)com>, andrew(at)tao11(dot)riddles(dot)org(dot)uk, PostgreSQL Hackers <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: FETCH FIRST clause WITH TIES option |
| Date: | 2019-01-16 08:45:46 |
| Message-ID: | CALAY4q-+CKiFkgCL5VSK-9P8i5Z9uoQQh6ZEZLkjzsUT2mySsw@mail.gmail.com |
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| Lists: | pgsql-hackers |
On Tue, Jan 15, 2019 at 2:51 PM Tomas Vondra <tomas(dot)vondra(at)2ndquadrant(dot)com>
wrote:
> What do you mean by "raw statistic"?
>
I mean without further calculation to consider other operation
>
> IMHO the best thing you can do is call estimate_num_groups() and combine
> that with the number of input rows. That shall benefit from ndistinct
> coefficients when available, etc. I've been thinking that considering
> the unreliability of grouping estimates we should use a multiple of the
> average size (because there may be much larger groups), but I think
> that's quite unprecipled and I'd much rather try without it first.
>
>
thank you for clarifying.
The attache patch use your suggestion uptread
regards
Surafel
| Attachment | Content-Type | Size |
|---|---|---|
| fetch_first_with_ties_v5.patch | text/x-patch | 28.4 KB |
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