Re: postgres_fdw bug in 9.6

On 2016/12/16 1:39, Tom Lane wrote:
> Etsuro Fujita <fujita(dot)etsuro(at)lab(dot)ntt(dot)co(dot)jp> writes:
>> On 2016/12/13 23:13, Ashutosh Bapat wrote:
>>> A possible short-term fix may be this: instead of picking any random
>>> path to stick into fdw_outerpath, we choose a path which covers the
>>> pathkeys of ForeignPath.

>> Seems reasonable.

> No, because GetExistingLocalJoinPath is called once per relation not once
> per path. Even if we were willing to eat the overhead of calling it once
> per path, we'd have to give up considering foreign paths with sort orders
> that there wasn't any cheap way to produce locally.

Hmm, I agree on that point that giving it up might result in a bad plan.

As I said upthread, an alternative I am thinking is (1) to create an
equivalent nestloop join path using inner/outer paths of a foreign join
path, except when that join path implements a full join, in which case a
merge/hash join path is used, (2) store it in fdw_outerpath as-is, and
(3) during an EPQ recheck, apply postgresRecheckForeignScan to the outer
subplan created from the fdw_outerpath as-is. What do you think about that?

Best regards,
Etsuro Fujita