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.
Thanks,
Amit
