Re: [HACKERS] Parallel tuplesort (for parallel B-Tree index creation)

On Wed, Jan 24, 2018 at 10:36 AM, Thomas Munro
<thomas(dot)munro(at)enterprisedb(dot)com> wrote:
> On Wed, Jan 24, 2018 at 5:59 PM, Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
>>>> I am going to repeat my previous suggest that we use a Barrier here.
>>>> Given the discussion subsequent to my original proposal, this can be a
>>>> lot simpler than what I suggested originally. Each worker does
>>>> BarrierAttach() before beginning to read tuples (exiting if the phase
>>>> returned is non-zero) and BarrierArriveAndDetach() when it's done
>>>> sorting. The leader does BarrierAttach() before launching workers and
>>>> BarrierArriveAndWait() when it's done sorting.
>>
>> How does leader detect if one of the workers does BarrierAttach and
>> then fails (either exits or error out) before doing
>> BarrierArriveAndDetach?
>
> If you attach and then exit cleanly, that's a programming error and
> would cause anyone who runs BarrierArriveAndWait() to hang forever.
>

Right, but what if the worker dies due to something proc_exit(1) or
something like that before calling BarrierArriveAndWait. I think this
is part of the problem we have solved in
WaitForParallelWorkersToFinish such that if the worker exits abruptly
at any point due to some reason, the system should not hang.

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