Re: Custom Scan APIs (Re: Custom Plan node)

On Mon, Mar 3, 2014 at 5:15 PM, Stephen Frost <sfrost(at)snowman(dot)net> wrote:
>> As I mentioned
>> up-thread, I'd really like to see FDW join push-down, FDW aggregate
>> push-down, parallel query execution, and parallel remote-FDW execution
>> and I don't see this CustomScan approach as the right answer to any of
>> those.
>
> In accordance with the above, what I'd like to see with this patch is
> removal of the postgres_fdw changes and any changes which were for that
> support. In addition, I'd like to understand why 'ctidscan' makes any
> sense to have as an example of what to use this for- if that's valuable,
> why wouldn't we simply implement that in core? I do want an example in
> contrib of how to properly use this capability, but I don't think that's
> it.

I suggested that example to KaiGai at last year's PGCon. It may
indeed be something we want to have in core, but right now we don't.

More generally, I think this discussion is focusing on the wrong set
of issues. The threshold issue for this patch is whether there is a
set of hook points that enable a workable custom-scan functionality,
and whether KaiGai has correctly identified them. In other words, I
think we should be worrying about whether KaiGai's found all of the
places that need to be modified to support a custom scan, and whether
the modifications he's made to each of those places are correct and
adequate. Whether he's picked the best possible example does not
strike me as a matter of principal concern, and it's far too late to
tell him he's got to go pick a different one at this point anyway.

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