Thread: Re: extended statistics n-distinct on multiple columns not used when join two tables
Re: extended statistics n-distinct on multiple columns not used when join two tables
(moving to -hackers) On Tue, 13 Jun 2023 at 21:30, Pavel Stehule <pavel.stehule@gmail.com> wrote: > út 13. 6. 2023 v 11:21 odesílatel James Pang (chaolpan) <chaolpan@cisco.com> napsal: >> When join two table on multiple columns equaljoin, rows estimation always use selectivity = multiplied by distinctmultiple 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? David
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Re: extended statistics n-distinct on multiple columns not used when join two tables
(moving to -hackers)
On Tue, 13 Jun 2023 at 21:30, Pavel Stehule <pavel.stehule@gmail.com> wrote:
> út 13. 6. 2023 v 11:21 odesílatel James Pang (chaolpan) <chaolpan@cisco.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?
David
RE: extended statistics n-distinct on multiple columns not used when join two tables
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.stehule@gmail.com>
Sent: Tuesday, June 13, 2023 7:29 PM
To: David Rowley <dgrowleyml@gmail.com>
Cc: PostgreSQL Developers <pgsql-hackers@lists.postgresql.org>; James Pang (chaolpan) <chaolpan@cisco.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@gmail.com> napsal:
(moving to -hackers)
On Tue, 13 Jun 2023 at 21:30, Pavel Stehule <pavel.stehule@gmail.com> wrote:
> út 13. 6. 2023 v 11:21 odesílatel James Pang (chaolpan) <chaolpan@cisco.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
Re: extended statistics n-distinct on multiple columns not used when join two tables
On Tue, 13 Jun 2023 at 23:29, Pavel Stehule <pavel.stehule@gmail.com> wrote: >> 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 Ok, I pushed that patch. Thanks. David