Re: Declarative partitioning - another take

On 2016/09/02 15:22, Ashutosh Bapat wrote:
>>
>>
>>> 2. A combination of constraints on the partitions should be applicable to
>>> the parent. We aren't doing that.
>>
>> How about on seeing that a RELOPT_OTHER_MEMBER_REL is partitioned parent
>> table, we can have get_relation_constraints() include a constant false
>> clause in the list of constraints returned for
>> relation_excluded_by_constraints() to process so that it is not included
>> in the append result by way of constraint exclusion. One more option is
>> to mark such rels dummy in set_rel_size().
>>
>>
> I am not complaining about having parent relation there. For the people who
> are used to seeing the parent relation in the list of append relations, it
> may be awkward. But +1 if we can do that. If we can't do that, we should at
> least mark with an OR of all constraints on the partitions, so that
> constraint exclusion can exclude it if there are conditions incompatible
> with constraints. This is what would happen in inheritance case as well, if
> there are constraints on the parent. In the above example, the parent table
> would have constraints CHECK ((a >= 0 AND a < 250) OR (a >= 250 and a <
> 500) OR (a >= 500 or a < 600)). It will probably get excluded, if
> constraint exclusion is smart enough to understand ORing.

I guess constraint exclusion would be (is) smart enough to handle that
correctly but why make it unnecessarily spend a *significant* amount of
time on doing the proof (when we *know* we can just skip it). Imagine how
long the OR list could get. By the way, my suggestion of just returning a
constant false clause also does not work - neither in case of a query with
restrictions (predicate has to be an OpExpr to go ahead with the proof
which constant false clause is not) nor in case of a query without
restrictions (proof is not performed at all). So, that one is useless.

Getting rid of the parent table in the append list by other means may be a
way to go. We know that the table is empty and safe to just drop.

Thanks,
Amit