Re: Using multiple extended statistics for estimates
От | Tomas Vondra |
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Тема | Re: Using multiple extended statistics for estimates |
Дата | |
Msg-id | 20191114155541.zliellgi2if4bb5f@development обсуждение исходный текст |
Ответ на | Re: Using multiple extended statistics for estimates (Mark Dilger <hornschnorter@gmail.com>) |
Ответы |
Re: Using multiple extended statistics for estimates
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Список | pgsql-hackers |
On Wed, Nov 13, 2019 at 10:04:36AM -0800, Mark Dilger wrote: > > >On 11/13/19 7:28 AM, Tomas Vondra wrote: >>Hi, >> >>here's an updated patch, with some minor tweaks based on the review and >>added tests (I ended up reworking those a bit, to make them more like >>the existing ones). > >Thanks, Tomas, for the new patch set! > >Attached are my review comments so far, in the form of a patch applied >on top of yours. > Thanks. 1) It's not clear to me why adding 'const' to the List parameters would be useful? Can you explain? 2) I think you're right we can change find_strongest_dependency to do /* also skip weaker dependencies when attribute count matches */ if (strongest->nattributes == dependency->nattributes && strongest->degree >= dependency->degree) continue; That'll skip some additional dependencies, which seems OK. 3) It's not clear to me what you mean by * TODO: Improve this code comment. Specifically, why would we * ignore that no rows will match? It seems that such a discovery * would allow us to return an estimate of 0 rows, and that would * be useful. added to dependencies_clauselist_selectivity. Are you saying we should also compute selectivity estimates for individual clauses and use Min() as a limit? Maybe, but that seems unrelated to the patch. regards -- Tomas Vondra http://www.2ndQuadrant.com PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
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