Re: crashes due to setting max_parallel_workers=0

On 26 March 2017 at 00:17, Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
> On Sat, Mar 25, 2017 at 6:31 PM, David Rowley
> <david(dot)rowley(at)2ndquadrant(dot)com> wrote:
>> On 25 March 2017 at 23:09, Rushabh Lathia <rushabh(dot)lathia(at)gmail(dot)com> wrote:
>>> Also another point which I think we should fix is, when someone set
>>> max_parallel_workers = 0, we should also set the
>>> max_parallel_workers_per_gather
>>> to zero. So that way it we can avoid generating the gather path with
>>> max_parallel_worker = 0.
>>
>> I see that it was actually quite useful that it works the way it does.
>> If it had worked the same as max_parallel_workers_per_gather, then
>> likely Tomas would never have found this bug.
>>
>> I wondered if there's anything we can do here to better test cases
>> when no workers are able to try to ensure the parallel nodes work
>> correctly, but the more I think about it, the more I don't see wrong
>> with just using SET max_parallel_workers = 0;
>>
>> My vote would be to leave the GUC behaviour as is and add some tests
>> to select_parallel.sql which exploit setting max_parallel_workers to 0
>> for running some tests.
>>
>
> I think force_parallel_mode=regress should test the same thing.

Not really. That flag's days are surely numbered. It creates a Gather
node, the problem was with GatherMerge.

--
David Rowley http://www.2ndQuadrant.com/
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