On 2/14/17 4:03 PM, Tom Lane wrote:
> Jim Nasby <Jim.Nasby@BlueTreble.com> writes:
>> On 2/14/17 1:18 PM, Tom Lane wrote:
>>> One point that could use further review is whether the de-duplication
>>> algorithm is actually correct. I'm only about 95% convinced by the
>>> argument I wrote in planunionor.c's header comment.
>
>> I'll put some thought into it and see if I can find any holes. Are you
>> only worried about the removal of "useless" rels or is there more?
>
> Well, the key point is whether it's really OK to de-dup on the basis
> of only the CTIDs that are not eliminated in any UNION arm. I was
> feeling fairly good about that until I thought of the full-join-to-
> left-join-to-no-join conversion issue mentioned in the comment.
> Now I'm wondering if there are other holes; or maybe I'm wrong about
> that one and it's not necessary to be afraid of full joins.
This patch applies cleanly (with offsets) and compiles at cccbdde.
Jim, have you had time to think about this? Any insights?
--
-David
david@pgmasters.net