From: | "James Pang (chaolpan)" <chaolpan(at)cisco(dot)com> |
---|---|
To: | Pavel Stehule <pavel(dot)stehule(at)gmail(dot)com>, David Rowley <dgrowleyml(at)gmail(dot)com> |
Cc: | PostgreSQL Developers <pgsql-hackers(at)lists(dot)postgresql(dot)org> |
Subject: | RE: extended statistics n-distinct on multiple columns not used when join two tables |
Date: | 2023-06-13 11:32:54 |
Message-ID: | PH0PR11MB519198036EB5D09B3D19BE52D655A@PH0PR11MB5191.namprd11.prod.outlook.com |
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Lists: | pgsql-hackers pgsql-performance |
Thanks for your information, yes, with multiple columns equal join and correlation , looks like extended statistics could help reduce “significantly rows estimation”. Hopefully it’s in future version.
James
From: Pavel Stehule <pavel(dot)stehule(at)gmail(dot)com>
Sent: Tuesday, June 13, 2023 7:29 PM
To: David Rowley <dgrowleyml(at)gmail(dot)com>
Cc: PostgreSQL Developers <pgsql-hackers(at)lists(dot)postgresql(dot)org>; James Pang (chaolpan) <chaolpan(at)cisco(dot)com>
Subject: Re: extended statistics n-distinct on multiple columns not used when join two tables
út 13. 6. 2023 v 13:26 odesílatel David Rowley <dgrowleyml(at)gmail(dot)com<mailto:dgrowleyml(at)gmail(dot)com>> napsal:
(moving to -hackers)
On Tue, 13 Jun 2023 at 21:30, Pavel Stehule <pavel(dot)stehule(at)gmail(dot)com<mailto:pavel(dot)stehule(at)gmail(dot)com>> wrote:
> út 13. 6. 2023 v 11:21 odesílatel James Pang (chaolpan) <chaolpan(at)cisco(dot)com<mailto:chaolpan(at)cisco(dot)com>> napsal:
>> When join two table on multiple columns equaljoin, rows estimation always use selectivity = multiplied by distinct multiple individual columns, possible to use extended n-distinct statistics on multiple columns?
>>
>> PG v14.8-1, attached please check test case with details.
>
> There is not any support for multi tables statistic
I think it's probably worth adjusting the docs to mention this. It
seems like it might be something that could surprise someone.
Something like the attached, maybe?
+1
Pavel
David
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