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

On 2016/01/28 12:58, Robert Haas wrote:
> On Thu, Jan 21, 2016 at 4:05 AM, Etsuro Fujita
> <fujita.etsuro@lab.ntt.co.jp> wrote:
>>> By the way, I'm not too sure I understand the need for the core
>>> changes that are part of this patch, and I think that point merits
>>> some discussion.  Whenever you change core like this, you're changing
>>> the contract between the FDW and core; it's not just postgres_fdw that
>>> needs updating, but every FDW.  So we'd better be pretty sure we need
>>> these changes and they are adequately justified before we think about
>>> putting them into the tree.  Are these core changes really needed
>>> here, or can we fix this whole issue in postgres_fdw and leave the
>>> core code alone?

>> Well, if we think it is the FDW's responsibility to insert a valid value for
>> tableoid in the returned slot during ExecForeignInsert, ExecForeignUpdate or
>> ExecForeignDelete, we don't need those core changes.  However, I think it
>> would be better that that's done by ModifyTable in the same way as
>> ForeignScan does in ForeignNext, IMO. That eliminates the need for
>> postgres_fdw or any other FDW to do that business in the callback routines.

> I'm not necessarily opposed to the core changes, but I want to
> understand better what complexity they are avoiding.  Can you send a
> version of this patch that only touches postgres_fdw, so I can
> compare?

Attached is that version of the patch.

I think that postgres_fdw might be able to insert a tableoid value in
the returned slot in e.g., postgresExecForeignInsert if AFTER ROW
Triggers or RETURNING expressions reference that value, but I didn't do
anything about that.

Best regards,
Etsuro Fujita