On 2016/06/17 21:45, Robert Haas wrote:
On Thu, Jun 16, 2016 at 10:44 PM, Etsuro Fujita
<fujita.ets...@lab.ntt.co.jp> wrote:
On 2016/06/16 22:00, Robert Haas wrote:
On Thu, Jun 16, 2016 at 7:05 AM, Etsuro Fujita
<fujita.ets...@lab.ntt.co.jp> wrote:

ISTM that a robuster solution to this is to push down the ft1-ft2-ft3
with the PHV by extending deparseExplicitTargetList() and/or something
so that we can send the remote query like:

select ft1.a, (ft3.a IS NOT NULL) from (ft1 inner join ft2 on ft1.a =
left join ft3 on ft1.a = ft3.a

I completely agree we should have that, but not for 9.6.

OK, I'll work on that for 10.0.

Great, that will be a nice improvement.

Here is a patch for that.

* Modified deparseExplicitTargetList as well as is_foreign_expr and deparseExpr so that a join is pushed down with PHVs if not only the join but the PHVs are safe to execute remotely. The existing deparsing logic can't build a remote query that involves subqueries, so the patch currently gives up pushing down any upper joins involving a join (or foreign table!) with PHVs in the tlist. But I think the patch would be easily extended to support that, once we support deparsing subqueries.

* Besides that, simplified foreign_join_ok a bit, by adding a new flag, allow_upper_foreign_join, to PgFdwRelationInfo, replacing the existing pushdown_safe flag with it. See the comments in postgres_fdw.h.

Comments welcome.

Best regards,
Etsuro Fujita

Attachment: pg-fdw-phv-handling-v1.patch
Description: application/download

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