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  1. Doc: mention that extended stats aren't used for joins

  1. extended statistics n-distinct on multiple columns not used when join two tables

    James Pang (chaolpan) <chaolpan@cisco.com> — 2023-06-13T09:21:25Z

    Hi,
     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.

Thanks,

James

  2. Re: extended statistics n-distinct on multiple columns not used when join two tables

    Pavel Stehule <pavel.stehule@gmail.com> — 2023-06-13T09:29:49Z

    Hi

út 13. 6. 2023 v 11:21 odesílatel James Pang (chaolpan) <chaolpan@cisco.com>
napsal:

> Hi,
>
>      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

Regards

Pavel


>
>
> Thanks,
>
>
>
> James
>
>
>

  3. Re: extended statistics n-distinct on multiple columns not used when join two tables

    David Rowley <dgrowleyml@gmail.com> — 2023-06-13T11:25:53Z

    (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

  4. Re: extended statistics n-distinct on multiple columns not used when join two tables

    Pavel Stehule <pavel.stehule@gmail.com> — 2023-06-13T11:28:34Z

    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
>

  5. RE: extended statistics n-distinct on multiple columns not used when join two tables

    James Pang (chaolpan) <chaolpan@cisco.com> — 2023-06-13T11:32:54Z

    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<mailto:dgrowleyml@gmail.com>> napsal:
(moving to -hackers)

On Tue, 13 Jun 2023 at 21:30, Pavel Stehule <pavel.stehule@gmail.com<mailto:pavel.stehule@gmail.com>> wrote:
> út 13. 6. 2023 v 11:21 odesílatel James Pang (chaolpan) <chaolpan@cisco.com<mailto: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

  6. Re: extended statistics n-distinct on multiple columns not used when join two tables

    David Rowley <dgrowleyml@gmail.com> — 2023-06-22T00:53:10Z

    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