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

On 21 August 2017 at 10:08, Amit Kapila <amit.kapila16@gmail.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