Re: why not parallel seq scan for slow functions

On Tue, Sep 19, 2017 at 1:17 PM, Thomas Munro <thomas(dot)munro(at)enterprisedb(dot)com
> wrote:

> On Thu, Sep 14, 2017 at 3:19 PM, Amit Kapila <amit(dot)kapila16(at)gmail(dot)com>
> wrote:
> > The attached patch fixes both the review comments as discussed above.
>
> This cost stuff looks unstable:
>
> test select_parallel ... FAILED
>
> ! Gather (cost=0.00..623882.94 rows=9976 width=8)
> Workers Planned: 4
> ! -> Parallel Seq Scan on tenk1 (cost=0.00..623882.94 rows=2494
> width=8)
> (3 rows)
>
> drop function costly_func(var1 integer);
> --- 112,120 ----
> explain select ten, costly_func(ten) from tenk1;
> QUERY PLAN
> ------------------------------------------------------------
> ----------------
> ! Gather (cost=0.00..625383.00 rows=10000 width=8)
> Workers Planned: 4
> ! -> Parallel Seq Scan on tenk1 (cost=0.00..625383.00 rows=2500
> width=8)
> (3 rows)
>

that should be fixed by turning costs on the explain, as is the tradition.

See attached.

Cheers,

Jeff