On Wed, Oct 4, 2017 at 3:45 PM, Etsuro Fujita
<fujita.etsuro@lab.ntt.co.jp> wrote:
> On 2017/10/03 18:16, Ashutosh Bapat wrote:
>>
>> Enforcing WCO constraints imposed by the local server on the row/DML
>> being passed to the foreign server is fine, but trying to impose them
>> on the row being inserted/updated at the foreign server looks odd. May
>> be we should just leave this case as it is. I am comparing this case
>> with the way we handle constraints on a foreign table.
>
>
> Hmm, I think that would be okay in the case where WCO constraints match
> constraints on the foreign table, but I'm not sure that would be okay even
> in the case where WCO constraints don't match? Consider:
>
> create table bt (a int check (a % 2 = 0));
> create foreign table ft (a int check (a % 2 = 0)) server loopback options
> (table_name 'bt');
> create view rw_view_2 as select * from ft where a % 2 = 0 with check option;
>
> In that case the WCO constraint matches the constraint on the foreign table,
> so there would be no need to ensure the WCO constraint locally (to make the
> explanation simple, we assume here that we don't have triggers on the remote
> end). BUT: for another auto-updatable view defined using the same foreign
> table like this:
>
> create view rw_view_4 as select * from ft where a % 4 = 0 with check option;
>
> how is the WCO constraint (ie, a % 4 = 0) ensured remotely, which is
> different from the constraint on the foreign table (ie, a % 2 = 0)? Maybe
> I'm missing something, though.
Just like the local constraints on a foreign table are not ensured on
remote table (unless user takes steps to make that sure), WCO defined
locally need not be (and probably can not be) ensured remotely. We can
check whether a row being sent from the local server to the foreign
server obeys WCO, but what foreign server does to that row is beyond
local server's scope.
--
Best Wishes,
Ashutosh Bapat
EnterpriseDB Corporation
The Postgres Database Company
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