Re: Getting sorted data from foreign server

On Tue, Oct 27, 2015 at 6:44 PM, Fabrízio de Royes Mello <
fabriziomello(at)gmail(dot)com> wrote:

>
>
> On Tue, Oct 27, 2015 at 5:26 AM, Ashutosh Bapat <
> ashutosh(dot)bapat(at)enterprisedb(dot)com> wrote:
> >
> >
> >
> > On Fri, Oct 23, 2015 at 2:43 AM, Robert Haas <robertmhaas(at)gmail(dot)com>
> wrote:
> >>
> >> On Wed, Oct 21, 2015 at 5:23 AM, Ashutosh Bapat
> >> <ashutosh(dot)bapat(at)enterprisedb(dot)com> wrote:
> >> > Increasing the sorting cost factor (when use_remote_estimates =
> false) from
> >> > 1.1 to 1.2 makes the difference disappear.
> >> >
> >> > Since the startup costs for postgres_fdw are large portion of total
> cost,
> >> > extra 10% of rest of the cost is comparable to 1% fuzzy limit. IMO, we
> >> > shouldn't bother too much about it as the path costs are not much
> different.
> >>
> >> My feeling is that cranking the sorting cost factor up to 20-25% would
> >> be a good idea, just so we have less unnecessary plan churn. I dunno
> >> if sorting always costs that much, but if a 10% cost overhead is
> >> really 1% because it only applies to a fraction of the cost, I don't
> >> think that's good. The whole point was to pick something large enough
> >> that we wouldn't take the sorted path unless we will benefit from the
> >> sort, and clearly that's not what happened here.
> >>
> >
> > PFA patch with the default multiplication factor for sort bumped up to
> 1.2.
> >
>
> +/* If no remote estimates, assume a sort costs 10% extra */
> +#define DEFAULT_FDW_SORT_MULTIPLIER 1.2
>
> The above comment should not be 20%?
>
> Ah! Here's patch with comment fixed.

--
Best Wishes,
Ashutosh Bapat
EnterpriseDB Corporation
The Postgres Database Company