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

On Thu, Jan 18, 2018 at 4:19 PM, Thomas Munro
<thomas.munro@enterprisedb.com> wrote:
> Hi,
>
> I'm mostly away from my computer this week -- sorry about that, but
> here are a couple of quick answers to questions directed at me:
>
> On Thu, Jan 18, 2018 at 4:22 PM, Peter Geoghegan <pg@bowt.ie> wrote:
>> On Wed, Jan 17, 2018 at 10:40 AM, Robert Haas <robertmhaas@gmail.com> wrote:
>
>>> It's true that the leader will know the value of nworkers_launched,
>>> but as the comment in LaunchParallelWorkers() says: "The caller must
>>> be able to tolerate ending up with fewer workers than expected, so
>>> there is no need to throw an error here if registration fails.  It
>>> wouldn't help much anyway, because registering the worker in no way
>>> guarantees that it will start up and initialize successfully."  So it
>>> seems to me that a much better plan than having the leader try to
>>> figure out how many workers failed to launch would be to just keep a
>>> count of how many workers did in fact launch.
>
> (If nworkers_launched can be silently over-reported, then does
> parallel_leader_participation = off have a bug?
>

Yes, and it is being discussed in CF entry [1].

[1] - https://commitfest.postgresql.org/16/1341/

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