| From: | Peter Geoghegan <pg(at)bowt(dot)ie> |
|---|---|
| To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
| Cc: | Tomas Vondra <tomas(dot)vondra(at)2ndquadrant(dot)com>, Robert Haas <robertmhaas(at)gmail(dot)com>, Rafia Sabih <rafia(dot)sabih(at)enterprisedb(dot)com>, Amit Kapila <amit(dot)kapila16(at)gmail(dot)com>, PostgreSQL Developers <pgsql-hackers(at)postgresql(dot)org>, Thomas Munro <thomas(dot)munro(at)enterprisedb(dot)com> |
| Subject: | Re: TPC-H Q20 from 1 hour to 19 hours! |
| Date: | 2017-06-11 17:54:53 |
| Message-ID: | CAH2-Wz=zPeLz4LPwWxyLTD=4T91Jeo088aP2y7pgMu2u8xtRBQ@mail.gmail.com |
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| Lists: | pgsql-hackers |
On Sun, Jun 11, 2017 at 10:36 AM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)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
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