Re: multivariate statistics (v19)

On 04/10/16 20:37, Dean Rasheed wrote:
> On 4 October 2016 at 04:25, Michael Paquier <michael(dot)paquier(at)gmail(dot)com> wrote:
>> OK. A second thing was related to the use of schemas in the new system
>> catalogs. As mentioned in [1], those could be removed.
>> [1]: https://www.postgresql.org/message-id/CAB7nPqTU40Q5_NSgHVoMJfbyH1HDtqMbFDJ+kwFJSpam35b3Qg@mail.gmail.com.
>>
> That doesn't work, because if the intention is to be able to one day
> support statistics across multiple tables, you can't assume that the
> statistics are in the same schema as the table.
>
> In fact, if multi-table statistics are to be allowed in the future, I
> think you want to move away from thinking of statistics as depending
> on and referring to a single table, and handle them more like views --
> i.e, store a pg_node_tree representing the from_clause and add
> multiple dependencies at statistics creation time. That was what I was
> getting at upthread when I suggested the alternate syntax, and also
> answers Tomas' question about how JOIN might one day be supported.
>
> Of course, if we don't think that we will ever support multi-table
> statistics, that all goes away, and you may as well make the
> statistics name local to the table, but I think that's a bit limiting.
> One way or the other, I think this is a question that needs to be
> answered now. My vote is to leave expansion room to support
> multi-table statistics in the future.
>
> Regards,
> Dean
>
>
I can see multi-table statistics being useful if one is trying to
optimise indexes for multiple joins.

Am assuming that the statistics can be accessed by the user as well as
the planner? (I've only lightly followed this thread, so I might have
missed, significant relevant details!)

Cheers,
Gavin