| From: | Simon Riggs <simon(at)2ndquadrant(dot)com> |
|---|---|
| To: | Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> |
| Cc: | Robert Haas <robertmhaas(at)gmail(dot)com>, Jeff Janes <jeff(dot)janes(at)gmail(dot)com>, Dilip Kumar <dilipbalaut(at)gmail(dot)com>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: why not parallel seq scan for slow functions |
| Date: | 2017-08-21 09:45:46 |
| Message-ID: | CANP8+jK1ek6Q9nRow9=MK1PaXkL_n5jh6EJ4po=XDXsjEHFXxQ@mail.gmail.com |
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| Lists: | pgsql-hackers |
On 21 August 2017 at 10:08, Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
> Thoughts?
This seems like a very basic problem for parallel queries.
The problem seems to be that we are calculating the cost of the plan
rather than the speed of the plan.
Clearly, a parallel task has a higher overall cost but a lower time to
complete if resources are available.
We have the choice of 1) adding a new optimizable quantity, or of 2)
treating cost = speed, so we actually reduce the cost of a parallel
plan rather than increasing it so it is more likely to be picked.
--
Simon Riggs http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
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