| From: | Etsuro Fujita <fujita(dot)etsuro(at)lab(dot)ntt(dot)co(dot)jp> |
|---|---|
| To: | Robert Haas <robertmhaas(at)gmail(dot)com> |
| Cc: | Ashutosh Bapat <ashutosh(dot)bapat(at)enterprisedb(dot)com>, "pgsql-hackers(at)postgresql(dot)org" <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: Odd system-column handling in postgres_fdw join pushdown patch |
| Date: | 2016-04-15 11:00:30 |
| Message-ID: | 5710C9CE.3060300@lab.ntt.co.jp |
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| Lists: | pgsql-hackers |
On 2016/04/14 13:04, Robert Haas wrote:
> On Wed, Apr 13, 2016 at 11:21 PM, Etsuro Fujita
> <fujita(dot)etsuro(at)lab(dot)ntt(dot)co(dot)jp> wrote:
>>>> 2. When a join is pushed down, deparse system columns using something
>>>> like "CASE WHEN r1.* IS NOT NULL THEN 0 END", except for the table OID
>>>> column, which gets deparsed with the table OID in place of 0. This
>>>> delivers the correct behavior in the presence of outer joins.
>>> I think that that would cause useless data transfer for such culumns.
>>> Why not set values locally for such columns?
> Because that doesn't work properly when there are outer joins
> involved.
Understood. It looks like I overlooked Ashutosh's mail about that.
Thanks, Robert and Ashutosh!
Best regards,
Etsuro Fujita
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