(2019/03/11 13:06), Tom Lane wrote:
Etsuro Fujita<fujita.ets...@lab.ntt.co.jp> writes:
The parallel safety of the final scan/join target is determined from the
grouping target, not that target, which [ is wrong ]
This would only affect plan quality a little bit, so I don't think we
need a regression test for this, either, but the fix might destabilize
existing plan choices, so we should apply it to HEAD only?
Is that the only possible outcome? Per Robert's summary quoted above,
it seems like it might be possible for the code to decide that the final
scan/join target to be parallel safe when it is not, leading to outright
wrong answers or query failures.
Maybe I'm missing something, but I think that if the final scan/join
target is not parallel-safe, then the grouping target would not be
parallel-safe either, by the construction of the two targets, so I don't
think that we have such a correctness issue.
Best regards,
Etsuro Fujita
