Re: Problem while updating a foreign table pointing to apartitioned table on foreign server

Hello.

At Wed, 05 Sep 2018 20:02:04 +0900, Etsuro Fujita  wrote in <5B8FB7AC.5020003@lab.ntt.co.jp>
> (2018/08/30 21:58), Etsuro Fujita wrote:
> > (2018/08/30 20:37), Kyotaro HORIGUCHI wrote:
> >> At Fri, 24 Aug 2018 21:45:35 +0900, Etsuro
> >> Fujita wrote
> >> in<5B7FFDEF.6020302@lab.ntt.co.jp>
> >>> (2018/08/21 11:01), Kyotaro HORIGUCHI wrote:
> >>>> At Tue, 14 Aug 2018 20:49:02 +0900, Etsuro
> >>>> Fujita wrote
> >>>> in<5B72C1AE.8010408@lab.ntt.co.jp>
> >>>>> (2018/08/09 22:04), Etsuro Fujita wrote:
> >>>>>> (2018/08/08 17:30), Kyotaro HORIGUCHI wrote:
> >>>
> >>>>> I spent more time looking at the patch. ISTM that the patch well
> >>>>> suppresses the effect of the tuple-descriptor expansion by making
> >>>>> changes to code in the planner and executor (and ruleutils.c), but I'm
> >>>>> still not sure that the patch is the right direction to go in, because
> >>>>> ISTM that expanding the tuple descriptor on the fly might be a wart.
> >>>
> >>>> The exapansion should be safe if the expanded descriptor has the
> >>>> same defitions for base columns and all the extended coulumns are
> >>>> junks. The junk columns should be ignored by unrelated nodes and
> >>>> they are passed safely as far as ForeignModify passes tuples as
> >>>> is from underlying ForeignScan to ForeignUpdate/Delete.
> >>>
> >>> I'm not sure that would be really safe. Does that work well when
> >>> EvalPlanQual, for example?
> 
> I was wrong here; I assumed here that we supported late locking for an
> UPDATE or DELETE on a foreign table, and I was a bit concerned that
> the approach you proposed might not work well with EvalPlanQual, but
> as described in fdwhandler.sgml, the core doesn't support for that:
> 
>      For an UPDATE or DELETE on a
>      foreign table, it
>      is recommended that the ForeignScan operation on
>      the target
>      table perform early locking on the rows that it fetches, perhaps via
>      the
>      equivalent of SELECT FOR UPDATE.  An FDW can detect
>      whether
>      a table is an UPDATE/DELETE
>      target at plan time
>      by comparing its relid to
>      root->parse->resultRelation,
>      or at execution time by using
>      ExecRelationIsTargetRelation().
>      An alternative possibility is to perform late locking within the
>      ExecForeignUpdate or
>      ExecForeignDelete
>      callback, but no special support is provided for this.
> 
> So, there would be no need to consider about EvalPlanQual.  Sorry for
> the noise.

I don't think it is a noise at all. Thank you for the pointer.

regards.

-- 
Kyotaro Horiguchi
NTT Open Source Software Center