Re: Getting sorted data from foreign server

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.

> --
> Robert Haas
> EnterpriseDB: http://www.enterprisedb.com
> The Enterprise PostgreSQL Company
>

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