Don't use partial unique indexes for unique proofs in the planner

Here we adjust relation_has_unique_index_for() so that it no longer makes
use of partial unique indexes as uniqueness proofs.  It is incorrect to
use these as the predicates used by check_index_predicates() to set
predOK makes use of not only baserestrictinfo quals as proofs, but also
qual from join conditions.  For relation_has_unique_index_for()'s case, we
need to know the relation is unique for a given set of columns before any
joins are evaluated, so if predOK was only set to true due to some join
qual, then it's unsafe to use such indexes in
relation_has_unique_index_for().  The final plan may not even make use
of that index, which could result in reading tuples that are not as
unique as the planner previously expected them to be.

Bug: #17975
Reported-by: Tor Erik Linnerud
Backpatch-through: 11, all supported versions
Discussion: https://postgr.es/m/17975-98a90c156f25c952%40postgresql.org

1 files changed, 4 insertions, 5 deletions

diff --git a/src/backend/optimizer/plan/analyzejoins.c b/src/backend/optimizer/plan/analyzejoins.c
index 9161c8a2964..5f3cce873a0 100644
--- a/src/backend/optimizer/plan/analyzejoins.c
+++ b/src/backend/optimizer/plan/analyzejoins.c
@@ -801,9 +801,9 @@ rel_supports_distinctness(PlannerInfo *root, RelOptInfo *rel)
 		/*
 		 * For a plain relation, we only know how to prove uniqueness by
 		 * reference to unique indexes.  Make sure there's at least one
-		 * suitable unique index.  It must be immediately enforced, and if
-		 * it's a partial index, it must match the query.  (Keep these
-		 * conditions in sync with relation_has_unique_index_for!)
+		 * suitable unique index.  It must be immediately enforced, and not a
+		 * partial index. (Keep these conditions in sync with
+		 * relation_has_unique_index_for!)
 		 */
 		ListCell   *lc;
 
@@ -811,8 +811,7 @@ rel_supports_distinctness(PlannerInfo *root, RelOptInfo *rel)
 		{
 			IndexOptInfo *ind = (IndexOptInfo *) lfirst(lc);
 
-			if (ind->unique && ind->immediate &&
-				(ind->indpred == NIL || ind->predOK))
+			if (ind->unique && ind->immediate && ind->indpred == NIL)
 				return true;
 		}
 	}