Re: A GUC to prevent leader processes from running subplans?

On Sun, Nov 12, 2017 at 9:18 AM, Thomas Munro
<thomas(dot)munro(at)enterprisedb(dot)com> wrote:
> On Sat, Oct 21, 2017 at 8:09 AM, Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
>> On Tue, Oct 17, 2017 at 7:27 AM, Thomas Munro
>> <thomas(dot)munro(at)enterprisedb(dot)com> wrote:
>>
>> I don't think overloading force_parallel_mode is a good idea, but
>> having some other GUC for this seems OK to me. Not sure I like
>> multiplex_gather, though.
>
> How about parallel_leader_participation = on|off? The attached
> version has it that way, and adds regression tests to exercise on, off
> and off-but-couldn't-start-any-workers for both kinds of gather node.
>
> I'm not sure why node->need_to_rescan is initialised by both
> ExecGatherInit() and ExecGather(). Only the latter's value matters,
> right?
>

I don't see anything like need_to_rescan in the GatherState node. Do
you intend to say need_to_scan_locally? If yes, then I think whatever
you said is right.

> I've added this to the January Commitfest.
>

+1 to this idea. Do you think such an option at table level can be
meaningful? We have a parallel_workers as a storage option for
tables, so users might want leader to participate in parallelism only
for some of the tables.

--
With Regards,
Amit Kapila.
EnterpriseDB: http://www.enterprisedb.com