(2019/04/01 15:23), Amit Langote wrote:
> On 2019/04/01 14:35, Etsuro Fujita wrote:
>> (2019/03/29 23:10), Alvaro Herrera wrote:
>>> On 2019-Mar-29, Tom Lane wrote:
>>>
>>>> Alvaro Herrera<alvherre@2ndquadrant.com> writes:
>>>>> On 2019-Mar-29, PG Bug reporting form wrote:
>>>>>> SQL Error [42809]: ERROR: cannot create index on foreign table
>>>>>> "msg_json"
>>
>>>> Really, what *ought* to happen in such a case is that the FDW gets
>>>> told about the command and has the opportunity to try to do something
>>>> corresponding to making an index.
>>
>> Interesting!
>
> +1
>
> Maybe, CHECK constraints on foreign tables are similar -- it merely
> asserts the condition that all of the rows in the remote table *must*
> satisfy so that the local server can do something useful with it, such as
> trying to exclude the table with constraint exclusion.
>
> I guess the intended benefit with allowing indexes would be similar -- a
> locally-defined index on a foreign table will help an FDW estimate the
> cost of a query accessing the table more efficiently than, for example,
> having to rely on some other relatively expensive alternative, such as
> use_remote_estimate in postgres_fdw's case.
Yeah, I think so. Another benefit I can think of would be: that would
probably allow us to support ON CONFLICT DO UPDATE for foreign tables.
I think the intended benefit would be large!
Best regards,
Etsuro Fujita
