Re: Should we add GUCs to allow partition pruning to be disabled?

On Tue, Apr 17, 2018 at 5:42 PM, Justin Pryzby <pryzby@telsasoft.com> wrote:

> On Wed, Apr 18, 2018 at 12:07:18PM +1200, David Rowley wrote:
> > In PG10 the planner's partition pruning could be disabled by changing
> > the constraint_exclusion GUC to off.  This is still the case for PG11,
> > but only for UPDATE and DELETE queries. There is currently no way to
> > disable partition pruning for SELECT.
> >
> > Should we allow this?
>
> > 3. No new GUCs / Do nothing.
>
> Maybe this is divergent from the details of the implementation; but, from a
> user's perspective: why not continue to use constraint_exclusion?
>
> I would suggest to add zero new GUCs:
>
> 0. constraint_exclusion={off,partition,on,PLANNER*,EXECUTOR*}
>

​My initial reaction is that we need to fix the bug introduced in v10 -
leaving constraint_exclusion working as it has historically and not affect
the new-as-of-10 ability to prune (maybe better termed as skip...)
partitions known during execution to contain no qualified tuples.

David J.