Re: Foreign join pushdown vs EvalPlanQual

On 2015/12/02 1:54, Robert Haas wrote:
> On Fri, Nov 27, 2015 at 1:25 AM, Kouhei Kaigai <kaigai(at)ak(dot)jp(dot)nec(dot)com> wrote:
>>> Sorry, I don't understand this. In my understanding, fdw_recheck_quals
>>> can be defined for a foreign join, regardless of the join type,

>> Yes, "can be defined", but will not be workable if either side of
>> joined tuple is NULL because of outer join. SQL functions returns
>> NULL prior to evaluation, then ExecQual() treats this result as FALSE.
>> However, a joined tuple that has NULL fields may be a valid tuple.
>>
>> We don't need to care about unmatched tuple if INNER JOIN.

> This is a really good point, and a very strong argument for the design
> KaiGai has chosen here.

Maybe my explanation was not enough. Sorry about that. But I mean that
we define fdw_recheck_quals for a foreign-join as quals that 1) were
extracted by extract_actual_join_clauses as "otherclauses"
(rinfo->is_pushed_down=true) and that 2) were pushed down to the remote
server, not scan quals relevant to all the base tables invoved in the
foreign-join. So in this definition, I think fdw_recheck_quals for a
foreign-join will be workable, regardless of the join type.

Best regards,
Etsuro Fujita