Re: Odd behavior in foreign table modification (Was: Re: Optimization for updating foreign tables in Postgres FDW)

On 8 January 2016 at 05:08, Etsuro Fujita <fujita(dot)etsuro(at)lab(dot)ntt(dot)co(dot)jp> wrote:
> On 2016/01/07 21:50, Etsuro Fujita wrote:
>>
>> On 2016/01/06 20:37, Thom Brown wrote:
>>>
>>> On 25 December 2015 at 10:00, Etsuro Fujita
>>> <fujita(dot)etsuro(at)lab(dot)ntt(dot)co(dot)jp> wrote:
>>>>
>>>> Attached is an updated version of the patch, which is
>>>> still WIP, but I'd be happy if I could get any feedback.
>
>
>>> I've run into an issue:
>>>
>>> *# UPDATE master_customers SET id = 22 WHERE id = 16 RETURNING
>>> tableoid::regclass;
>>> ERROR:
>>> CONTEXT: Remote SQL command: UPDATE public.customers SET id = 22
>>> WHERE ((id = 16)) RETURNING NULL
>
>
>> Will fix.
>
>
> While working on this, I noticed that the existing postgres_fdw system shows
> similar behavior, so I changed the subject.
>
> IIUC, the reason for that is when the local query specifies "RETURNING
> tableoid::regclass", the FDW has fmstate->has_returning=false while the
> remote query executed at ModifyTable has "RETURNING NULL", as shown in the
> above example; that would cause an abnormal exit in executing the remote
> query in postgresExecForeignUpdate, since that the FDW would get
> PGRES_TUPLES_OK as a result of the query while the FDW would think that the
> right result to get should be PGRES_COMMAND_OK, from the flag
> fmstate->has_returning=false.
>
> Attached is a patch to fix that.

I can't apply this patch in tandem with FDW DML pushdown patch (either
v2 or v3).

Thom