Re: multivariate statistics (v19)

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