Re: [HACKERS] TPC-H Q20 from 1 hour to 19 hours!

On Sun, Jun 11, 2017 at 10:36 AM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
>> Do you mean teaching the optimizer to do something like this?:
>
> Uh, no.  I don't think we want to add any run-time checks.  The point in
> this example is that we'd get a better rowcount estimate if we noticed
> that the FK constraint could be considered while estimating the size of
> the partsupp-to-aggregated-subquery join.

Sorry for not considering the context of the thread more carefully.
Robert said something about selectivity estimation and TPC-H to me,
which I decide to research; I then rediscovered this thread.

Clearly Q20 is designed to reward systems that do better with moving
predicates into subqueries, as opposed to systems with better
selectivity estimation.

-- 
Peter Geoghegan