Re: inherit support for foreign tables

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Etsuro Fujita <fujita(dot)etsuro(at)lab(dot)ntt(dot)co(dot)jp>
Cc: Ashutosh Bapat <ashutosh(dot)bapat(at)enterprisedb(dot)com>, Kyotaro HORIGUCHI <horiguchi(dot)kyotaro(at)lab(dot)ntt(dot)co(dot)jp>, Heikki Linnakangas <hlinnakangas(at)vmware(dot)com>, Noah Misch <noah(at)leadboat(dot)com>, Shigeru Hanada <shigeru(dot)hanada(at)gmail(dot)com>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: inherit support for foreign tables
Date: 2015-04-26 00:47:04
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Etsuro Fujita <fujita(dot)etsuro(at)lab(dot)ntt(dot)co(dot)jp> writes:
> On 2015/04/16 16:05, Etsuro Fujita wrote:
>> I agree with you on this point. However, ISTM there is a bug in
>> handling OIDs on foreign tables; while we now allow for ALTER SET
>> WITH/WITHOUT OIDS, we still don't allow the default_with_oids parameter
>> for foreign tables. I think that since CREATE FOREIGN TABLE should be
>> consistent with ALTER FOREIGN TABLE, we should also allow the parameter
>> for foreign tables. Attached is a patch for that.

> I also updated docs. Attached is an updated version of the patch.

I believe that we intentionally did not do this, and here is why not:
existing pg_dump files assume that default_with_oids doesn't affect any
relation type except plain tables. pg_backup_archiver.c only bothers
to change the GUC when about to dump a plain table, and otherwise leaves
it at its previous value. That means if we apply a patch like this, it's
entirely possible that pg_dump/pg_restore will result in foreign tables
accidentally acquiring OID columns.

Since default_with_oids is really only meant as a backwards-compatibility
hack, I don't personally have a problem with restricting it to act only on
plain tables. However, it might be a good idea to explicitly document
this interaction in a code comment to prevent anyone from re-inventing
this idea... I'll go do that.

regards, tom lane

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