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

On 12 January 2016 at 11:49, Etsuro Fujita <fujita.etsuro@lab.ntt.co.jp> wrote:
> 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.

The patch seems to work for me:

Before:

*# UPDATE master_customers SET id = 22 WHERE id = 1 RETURNING
tableoid::regclass;
ERROR:
CONTEXT:  Remote SQL command: UPDATE public.customers SET id = $2
WHERE ctid = $1 RETURNING NULL

After:

*# UPDATE master_customers SET id = 22 WHERE id = 1 RETURNING
tableoid::regclass;    tableoid
------------------remote.customers
(1 row)

UPDATE 1

Thom