Re: [HACKERS] parallel.c oblivion of worker-startup failures

On Fri, Jan 19, 2018 at 10:59 PM, Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
> The patch doesn't apply cleanly on the head, but after rebasing it, I
> have reviewed and tested it and it seems to be working fine. Apart
> from this specific issue, I think we should consider making
> nworkers_launched reliable (at the very least for cases where it
> matters). You seem to be of opinion that can be a source of subtle
> bugs which I don't deny but now I think we are starting to see some
> use cases of such a mechanism as indicated by Peter G. in parallel
> create index thread. Even, if we find some way for parallel create
> index to not rely on that assumption, I won't be surprised if some
> future parallelism work would have such a requirement.

Isn't making nworkers_launched reliable exactly what this patch does?
It converts the rare cases in which nworkers_launched would have been
unreliable into errors, precisely so that code like parallel CREATE
INDEX doesn't need to worry about the case where it's inaccurate.

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Robert Haas
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