From: Richard Guo <rguo@postgresql.org>
Date: Wed, 4 Mar 2026 01:57:43 +0000 (+0900)
Subject: Remove redundant restriction checks in apply_child_basequals
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=1f4f87d79436cd04d549b3ad0a141a7a3adca28c;p=thirdparty%2Fpostgresql.git

Remove redundant restriction checks in apply_child_basequals

In apply_child_basequals, after translating a parent relation's
restriction quals for a child relation, we simplify each child qual by
calling eval_const_expressions.  Historically, the code then called
restriction_is_always_false and restriction_is_always_true to reduce
NullTest quals that are provably false or true.

However, since commit e2debb643, the planner natively performs
NullTest deduction during constant folding.  Therefore, calling
restriction_is_always_false and restriction_is_always_true immediately
afterward is redundant and wastes CPU cycles.  We can safely remove
them and simply rely on the constant folding to handle the deduction.

Author: Richard Guo <guofenglinux@gmail.com>
Discussion: https://postgr.es/m/CAMbWs4-vLmGXaUEZyOMacN0BVfqWCt2tM-eDVWdDfJnOQaauGg@mail.gmail.com
---

diff --git a/src/backend/optimizer/util/inherit.c b/src/backend/optimizer/util/inherit.c
index 48b5d0aac4c..8d623bf136d 100644
--- a/src/backend/optimizer/util/inherit.c
+++ b/src/backend/optimizer/util/inherit.c
@@ -826,8 +826,7 @@ expand_appendrel_subquery(PlannerInfo *root, RelOptInfo *rel,
 /*
  * apply_child_basequals
  *		Populate childrel's base restriction quals from parent rel's quals,
- *		translating Vars using appinfo and re-checking for quals which are
- *		constant-TRUE or constant-FALSE when applied to this child relation.
+ *		translating them using appinfo.
  *
  * If any of the resulting clauses evaluate to constant false or NULL, we
  * return false and don't apply any quals.  Caller should mark the relation as
@@ -902,16 +901,9 @@ apply_child_basequals(PlannerInfo *root, RelOptInfo *parentrel,
 										   rinfo->security_level,
 										   NULL, NULL, NULL);
 
-			/* Restriction is proven always false */
-			if (restriction_is_always_false(root, childrinfo))
-				return false;
-			/* Restriction is proven always true, so drop it */
-			if (restriction_is_always_true(root, childrinfo))
-				continue;
-
 			childquals = lappend(childquals, childrinfo);
 			/* track minimum security level among child quals */
-			cq_min_security = Min(cq_min_security, rinfo->security_level);
+			cq_min_security = Min(cq_min_security, childrinfo->security_level);
 		}
 	}
 
diff --git a/src/backend/optimizer/util/relnode.c b/src/backend/optimizer/util/relnode.c
index a714c83f1ba..d21b4d3bb35 100644
--- a/src/backend/optimizer/util/relnode.c
+++ b/src/backend/optimizer/util/relnode.c
@@ -394,21 +394,13 @@ build_simple_rel(PlannerInfo *root, int relid, RelOptInfo *parent)
 			break;
 	}
 
-	/*
-	 * We must apply the partially filled in RelOptInfo before calling
-	 * apply_child_basequals due to some transformations within that function
-	 * which require the RelOptInfo to be available in the simple_rel_array.
-	 */
-	root->simple_rel_array[relid] = rel;
-
 	/*
 	 * Apply the parent's quals to the child, with appropriate substitution of
-	 * variables.  If the resulting clause is constant-FALSE or NULL after
-	 * applying transformations, apply_child_basequals returns false to
-	 * indicate that scanning this relation won't yield any rows.  In this
-	 * case, we mark the child as dummy right away.  (We must do this
-	 * immediately so that pruning works correctly when recursing in
-	 * expand_partitioned_rtentry.)
+	 * variables.  If any resulting clause is reduced to constant FALSE or
+	 * NULL, apply_child_basequals returns false to indicate that scanning
+	 * this relation won't yield any rows.  In this case, we mark the child as
+	 * dummy right away.  (We must do this immediately so that pruning works
+	 * correctly when recursing in expand_partitioned_rtentry.)
 	 */
 	if (parent)
 	{
@@ -418,13 +410,17 @@ build_simple_rel(PlannerInfo *root, int relid, RelOptInfo *parent)
 		if (!apply_child_basequals(root, parent, rel, rte, appinfo))
 		{
 			/*
-			 * Restriction clause reduced to constant FALSE or NULL.  Mark as
-			 * dummy so we won't scan this relation.
+			 * A restriction clause reduced to constant FALSE or NULL after
+			 * substitution.  Mark the child as dummy so that it need not be
+			 * scanned.
 			 */
 			mark_dummy_rel(rel);
 		}
 	}
 
+	/* Save the finished struct in the query's simple_rel_array */
+	root->simple_rel_array[relid] = rel;
+
 	return rel;
 }