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 join with the PHV by extending deparseExplicitTargetList() and/or something else 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 = ft2.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
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