Re: fixing consider_parallel for upper planner rels

On Fri, Jul 1, 2016 at 10:52 AM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> Robert Haas <robertmhaas(at)gmail(dot)com> writes:
>> On Thu, Jun 30, 2016 at 5:54 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>>> And the point of that is what, exactly? If the only change is that
>>> "some restrictions get enforced", I am not clear on why we need such
>>> a test mode in cases where the planner is afraid to put a top Gather on
>>> the plan. In particular, given the coding as you now have it, it seems
>>> like the only case where there's any difference is where we set
>>> glob->parallelModeOK but nonetheless end up with a not-parallel-safe
>>> topmost path (that doesn't have a Gather within it). It's not clear
>>> to me why having the executor switch into parallel mode makes sense at
>>> all with such a plan.
>
>> Suppose you create a PL/pgsql function that does an UPDATE and mark it
>> PARALLEL RESTRICTED. You wonder whether you've marked it correctly.
>> You can set force_parallel_mode=on and SELECT myfunc(). The
>> subsequent ERROR tells you that you've mismarked it.
>
> Right, but that statement is still true with the logic I'm imagining.
> I would also argue that the existing text in config.sgml explaining
> what this parameter does corresponds much more nearly to what I'm
> suggesting than to what you say the semantics are.

I just went and reread that description and it looks to me like it
matches what I said. I guess I don't really understand what exactly
you want to change.

--
Robert Haas
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