On Tue, Oct 10, 2017 at 1:31 PM, David Rowley
<david.rowley@2ndquadrant.com> wrote:
>
> I don't think there's any need to invent any new GUC. You could just
> divide cpu_tuple_cost by something.
>
> I did a quick benchmark on my laptop to see how much Append really
> costs, and with the standard costs the actual cost seems to be about
> cpu_tuple_cost / 2.4. So probably cpu_tuple_cost / 2 might be
> realistic. create_set_projection_path() does something similar and
> brincostestimate() does some similar magic and applies 0.1 *
> cpu_operator_cost to the total cost.
>
>
> # -- How does that compare to the cpu_tuple_cost?
> # select current_Setting('cpu_tuple_cost')::float8 / 0.00416630302337493743;
> ?column?
> ----------------
> 2.400209476818
> (1 row)
>
> Maybe it's worth trying with different row counts to see if the
> additional cost is consistent, but it's probably not worth being too
> critical here.
>
This looks good to me. I think it should be a separate, yet very small patch.
--
Best Wishes,
Ashutosh Bapat
EnterpriseDB Corporation
The Postgres Database Company
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