Alban Hertroys <haram...@gmail.com> writes:
> On Sep 7, 2013, at 6:54, Steve Atkins <st...@blighty.com> wrote:
>>> If I have a partitioned table that has some range constraints that look
>>> kinda like they're intended for constraint exclusion, but aren't quite
>>> non-overlapping, will that break anything?
> Next to that, putting data in the tables becomes ambiguous for records that
> match both constraints - in which table should the records go? That is
> something that you need to do programatically anyway, so with the knowledge
> of how to decide which records go where, you could also define your exclusion
> constraints to not be ambigous.
> I don't see any benefit of having ambiguous exclusion constraints - IMHO
> you're better off fixing them.
I agree with that advice in principle; but if the true partitioning
constraint is too complicated, you might defeat the planner's ability to
prove that particular tables don't need to be scanned as a consequence of
a particular WHERE clause. The simple range constraints Steve showed
should work fine with constraint exclusion. The proofs are done
separately for each sub-table, so the fact that the ranges overlap doesn't
bother the planner. We might in future have a more efficient partitioning
method that does assume non-overlapping ranges ... but it's not there
today.
regards, tom lane
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