Re: postgres_fdw bug in 9.6

From: Etsuro Fujita <fujita(dot)etsuro(at)lab(dot)ntt(dot)co(dot)jp>
To: Robert Haas <robertmhaas(at)gmail(dot)com>
Cc: Jeff Janes <jeff(dot)janes(at)gmail(dot)com>, David Steele <david(at)pgmasters(dot)net>, Ashutosh Bapat <ashutosh(dot)bapat(at)enterprisedb(dot)com>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: postgres_fdw bug in 9.6
Date: 2017-04-11 09:13:27
Message-ID: 2db008b4-9bf6-734a-4a56-cb457f12c2cc@lab.ntt.co.jp
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On 2017/04/08 3:33, Robert Haas wrote:
> On Mon, Apr 3, 2017 at 2:12 AM, Etsuro Fujita
> <fujita(dot)etsuro(at)lab(dot)ntt(dot)co(dot)jp> wrote:
>> On 2017/04/01 1:32, Jeff Janes wrote:
>>> On Thu, Mar 23, 2017 at 5:20 AM, Etsuro Fujita
>>> <fujita(dot)etsuro(at)lab(dot)ntt(dot)co(dot)jp <mailto:fujita(dot)etsuro(at)lab(dot)ntt(dot)co(dot)jp>> wrote:
>>> Done. Attached is a new version of the patch.
>>> Is the fix for 9.6.3 going to be just a back port of this, or will it
>>> look different?
>>
>> +1 for backporting; although that requires that GetForeignJoinPaths be
>> updated so that the FDW uses a new function to create an alternative local
>> join path (ie, CreateLocalJoinPath), that would make maintenance of the code
>> easy.
>
> Well, the problem here is that this breaks ABI compatibility. If we
> applied this to 9.6, and somebody tried to use a previously-compiled
> FDW .so against a new server version, it would fail after the upgrade,
> because the new server wouldn't have GetExistingLocalJoinPath and also
> possibly because of the change to the structure of JoinPathExtraData.
> Maybe there's no better alternative, and maybe nothing outside of
> postgres_fdw is using this stuff anyway, but it seems like a concern.

Yeah, but I was thinking that it'd be a good idea to add a note about
that to the release notes, to avoid such troubles.

> Also, the CommitFest entry for this seems to be a bit sketchy. It
> claims that Tom Lane is a co-author of this patch which, AFAICS, is
> not the case. It is listed under Miscellaneous rather than "Bug
> Fixes", which seems like a surprising decision. And it uses a subject
> line which is neither very clear nor the same as the (also not
> particularly helpful) subject line of the email thread.

Thanks for correcting that!

Best regards,
Etsuro Fujita

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