Re: executor relation handling

On 2018/10/08 9:29, David Rowley wrote:
> On 8 October 2018 at 13:13, Tom Lane <tgl@sss.pgh.pa.us> wrote:
>> The idea I had in mind was to allow hard pruning of any leaf that's
>> been excluded *at plan time* based on partition constraints seen in
>> its parent rel(s).  That should be safe enough as long as we take
>> locks on all the non-leaf rels --- then we'd know about any change
>> in the constraint situation.
>>
>> Rather than coping with renumbering the RTEs, it might be easiest
>> to invent an "RTE_DUMMY" RTE type that a hard-pruned RTE could be
>> changed to.
> 
> The problem with that is that, if we get [1] done in PG12, then the
> RTE_DUMMYs would not exist, as we'd only have RTEs in the range table
> for partitions that survived plan-time pruning.
...

> [1] https://commitfest.postgresql.org/20/1778/

Yeah, the patch proposed at [1] postpones creating partition RTEs (hence
locking them) to a point after pruning, which also means we create only
the necessary RTEs.  In fact, it's not just the RTEs, but child
PlanRowMarks, whose creation is postponed to after pruning.  So, I
admitted upthread that my proposed patch here would only add code that
will become useless if we're able to get [1] in.

Thanks,
Amit