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

On 2016/01/12 20:36, Thom Brown wrote:
> On 8 January 2016 at 05:08, Etsuro Fujita <fujita.etsuro@lab.ntt.co.jp> wrote:

>>> On 2016/01/06 20:37, Thom Brown wrote:
>>>> 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

>> 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).

That patch is for fixing the similar issue in the existing postgres_fdw 
system.  So, please apply that patch without the DML pushdown patch.  If 
that patch is reasonable as a fix for the issue, I'll update the DML 
pushdown patch (v3) on top of that patch.

Best regards,
Etsuro Fujita