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

On Sat, Mar 24, 2018 at 9:40 AM, Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> 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
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company