Re: [HACKERS] Add support for tuple routing to foreign partitions

(2018/03/23 20:55), Etsuro Fujita wrote:
> (2018/03/23 4:09), Robert Haas wrote:
>> 1. It still doesn't work for COPY, because COPY isn't going to have a
>> ModifyTableState. I really think it ought to be possible to come up
>> with an API that can handle both INSERT and COPY; I don't think it
>> should be necessary to have two different APIs for those two problems.
>> Amit managed to do it for regular tables, and I don't really see a
>> good reason why foreign tables need to be different.
>
> Maybe I'm missing something, but I think the proposed FDW API could be
> used for the COPY case as well with some modifications to core. If so,
> my question is: should we support COPY into foreign tables as well? I
> think that if we support COPY tuple routing for foreign partitions, it
> would be better to support direct COPY into foreign partitions as well.

Done.

>> 2. I previously asked why we couldn't use the existing APIs for this,
>> and you gave me some answer, but I can't help noticing that
>> postgresExecForeignRouting is an exact copy of
>> postgresExecForeignInsert. Apparently, some code reuse is indeed
>> possible here! Why not reuse the same function instead of calling a
>> new one? If the answer is that planSlot might be NULL in this case,
>> or something like that, then let's just document that. A needless
>> proliferation of FDW APIs is really undesirable, as it raises the bar
>> for every FDW author.
>
> You've got a point! I'll change the patch that way.

Done.  I modified the patch so that the existing API 
postgresExecForeignInsert is called as-is (ie, with the planSlot 
parameter) in the INSERT case and is called with that parameter set to 
NULL in the COPY case.  So, I removed postgresExecForeignRouting and the 
postgres_fdw refactoring for that API.  Also, I changed the names of the 
remaining new APIs to postgresBeginForeignInsert and 
postgresEndForeignInsert, which I think would be better because these 
are used not only for tuple routing but for directly copying into 
foreign tables.  Also, I dropped partition_index from the parameter list 
for postgresBeginForeignInsert; I thought that it could be used for the 
FDW to access the partition info stored in mt_partition_tuple_routing 
for something in the case of tuple-routing, but I started to think that 
the FDW wouldn't need that in practice.

>> However, I think that getting INSERT
>> but not COPY, with bad performance, and with duplicated APIs, is
>> moving more in the wrong direction than the right one.
>
> Will fix.

Done.

Attached is the new version of the patch.  Patch 
foreign-routing-fdwapi-2.patch is created on top of patch 
postgres-fdw-refactoring-2.patch.  (The former contains the bug-fix 
[1].)  Any feedback is welcome!

Best regards,
Etsuro Fujita

[1] https://www.postgresql.org/message-id/5ABA4074.1090500@lab.ntt.co.jp