Re: planner support functions: handle GROUP BY estimates ?
От | Tomas Vondra |
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Тема | Re: planner support functions: handle GROUP BY estimates ? |
Дата | |
Msg-id | 20200114221247.xjuioweczqvq6zdt@development обсуждение исходный текст |
Ответ на | Re: planner support functions: handle GROUP BY estimates ? (Tom Lane <tgl@sss.pgh.pa.us>) |
Ответы |
Re: planner support functions: handle GROUP BY estimates ?
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Список | pgsql-hackers |
On Tue, Jan 14, 2020 at 04:52:44PM -0500, Tom Lane wrote: >Tomas Vondra <tomas.vondra@2ndquadrant.com> writes: >> On Tue, Jan 14, 2020 at 04:21:57PM -0500, Tom Lane wrote: >>> Yeah, it seems likely to me that the infrastructure for this would be >>> somewhat different --- the user-facing syntax could be basically the >>> same, but ultimately we want to generate entries in pg_statistic not >>> pg_statistic_ext_data. Or at least entries that look the same as what >>> you could find in pg_statistic. > >> Yeah. I think we could invent a new type of statistics "expressions" >> which would simply built this per-column stats. So for example >> CREATE STATISTICS s (expressions) ON (a*b), sqrt(c) FROM t; > >I was imagining the type keyword as being "standard" or something >like that, since what it's going to build are the "standard" kinds >of stats for the expression's datatype. But yeah, has to be some other >keyword than the existing ones. > >The main issue for sticking the results into pg_statistic is that >the primary key there is (starelid, staattnum), and we haven't got >a suitable attnum. I wouldn't much object to putting the data into >pg_statistic_ext_data, but it doesn't really have a suitable >rowtype ... Well, that's why I proposed to essentially build a fake "relation" just for this purpose. So we'd have a pg_class entry with a special relkind, attnums and all that. And the expressions would be stored either in pg_statistic_ext or in a new catalog. But maybe that's nonsense. regards -- Tomas Vondra http://www.2ndQuadrant.com PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
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