Re: [HACKERS] why not parallel seq scan for slow functions

On Sat, Mar 24, 2018 at 9:40 AM, Amit Kapila  wrote:
> For me, it is equivalent to the master.  The average of ten runs on
> the master is 20664.3683 and with all the patches applied it is
> 20590.4734.  I think there is some run-to-run variation, but more or
> less there is no visible degradation.  I think we have found the root
> cause and eliminated it.  OTOH, I have found another case where new
> patch series seems to degrade.

All right, I have scaled my ambitions back further.  Here is a revised
and slimmed-down version of the patch series.  If we forget about
"Remove explicit path construction logic in create_ordered_paths" for
now, then we don't really need a new upperrel.  So this patch just
modifies the toplevel scan/join rel in place, which should avoid a
bunch of overhead in add_path() and other places, while hopefully
still fixing the originally-reported problem.  I haven't tested this
beyond verifying that it passes the regression test, but I've run out
of time for today.

-- 
Robert Haas
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