Richard Guo <[email protected]> 于2026年9月4日周五 15:49写道： > > On Thu, Sep 3, 2026 at 6:39 PM Tender Wang <[email protected]> wrote: > > I also noticed that the resulting plan contains a duplicated filter: > > > This is not introduced by v1; I can reproduce the same duplicate qual on > > pg16.14 as well, so it seems to be a pre-existing issue. > > Right, this is a pre-existing issue, and is exposed by the new test > case. > > + -> Subquery Scan on t3 > + Filter: ((b.q1 = t3.cnt) AND (b.q1 = t3.cnt)) > > I looked into it. What happens here is that outer-join identity 3 > permits the join to t3 to commute with the a/b left join, so we > generate multiple clones of "b.q1 = t3.cnt", differing in the > nullingrels of b.q1. Only one of them should be applied in any given > plan. However, when movable join clauses are pushed down into a > parameterized path, we fail to choose among the clones. In this > example, t3's lateral reference to a PlaceHolderVar evaluated at the > a/b join forces every path for t3 to be parameterized by a set that > includes that outer join's relid, making both clones movable into the > scan. The same thing can also happen for clauses moved down into a > parameterized join.
Yes, I learned the code and got the same conclusion. > > I think we need to fix this. It wastes effort evaluating the same > qual clause repeatedly. What is worse, it applies the clause's > selectivity multiple times, underestimating the result's row count. > Agree > Attached is a patch that teaches get_baserel_parampathinfo and > get_joinrel_parampathinfo to check incompatible_relids. A clone > should not be enforced if an outer join it is incompatible with has > already been computed. > > Thoughts? The patch looks good to me. One minor comment about the wording: ... A clone clause must not be enforced here if an outer join it is incompatible with has already been computed ... ... I found "an outer join it is incompatible with has ..." a bit difficult to parse. Would it be clearer to add "that" here? ... A clone clause must not be enforced here if an outer join that it is incompatible with has already been computed ... ... -- Thanks, Tender Wang
