Re: postgres_fdw bug in 9.6

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.

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.

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