On Mon, Jun 13, 2016 at 5:27 PM, Robert Haas <robertmhaas@gmail.com> wrote:
> On Mon, Jun 13, 2016 at 4:46 PM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
>> Robert Haas <robertmhaas@gmail.com> writes:
>>> In practice, we don't yet have the ability for
>>> parallel-safe paths from subqueries to affect planning at higher query
>>> levels, but that's because the pathification stuff landed too late in
>>> the cycle for me to fully react to it.
>>
>> I wonder if that's not just from confusion between subplans and
>> subqueries. I don't believe any of the claims made in the comment
>> adjusted in the patch below (other than "Subplans currently aren't passed
>> to workers", which is true but irrelevant). Nested Gather nodes is
>> something that you would need, and already have, a defense for anyway.
>
> I think you may be correct.
Oh, one other thing about this: I'm not going to try to defend
whatever confusion between subplans and subqueries appears in that
comment, but prior to upper planner pathification I think we were dead
in the water here anyway, because the subquery was going to output a
finished plan, not a list of paths. Since finished plans aren't
labeled as to parallel-safety, we'd have to conservatively assume that
the finished plan we got back might not be parallel-safe. Now that
we're using the path representation throughout, we can do better.
--
Robert Haas
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