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

On Wed, Jan 20, 2016 at 4:50 AM, Etsuro Fujita
<fujita.etsuro@lab.ntt.co.jp> wrote:
> My concern about that is that would make the code in deparseTargetList()
> complicated.
>
> Essentially, I think your propossal needs a two-pass algorithm for
> deparseTargetList; (1) create an integer List of the columns being retrieved
> from the given attrs_used (getRetrievedAttrs()), and (2) print those columns
> (printRetrievedAttrs()).  How about sharing those two functions between
> deparseTargetList and deparseReturningList?:

I don't see why we'd need that.  I adjusted the code in postgres_fdw
along the lines I had in mind and am attaching the result.  It doesn't
look complicated to me, and it passes the regression test you 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?

--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company