According to CFbot this patch fails to apply. Richard, can you send an update, please?
Also, I see that the thread was inactive for a while. Are you going to continue this work? I think it would be helpful, if you could write a short recap about current state of the patch and list open questions for reviewers.
The new status of this patch is: Waiting on Author
Thanks Anastasia. I've rebased the patch with latest master.
To recap, the problem we are fixing here is when generating join clauses from equivalence classes, we only select the joinclause with the 'best score', or the first joinclause with a score of 3. This may cause us to miss some joinclause on partition keys and thus fail to generate partitionwise join.
The initial idea for the fix is to create all the RestrictInfos from ECs in order to check whether there exist equi-join conditions involving pairs of matching partition keys of the relations being joined for all partition keys. And then Tom proposed a much better idea which leverages function exprs_known_equal() to tell whether the partkeys can be found in the same eclass, which is the current implementation in the latest patch.
