Fix set_append_rel_pathlist() to deal intelligently with cases where

substituting a child rel's output expressions into the appendrel's restriction
clauses yields a pseudoconstant restriction.  We might be able to skip scanning
that child rel entirely (if we get constant FALSE), or generate a one-time
filter.  8.3 more or less accidentally generated plans that weren't completely
stupid in these cases, but that was only because an extra recursive level of
subquery_planner() always occurred and allowed const-simplification to happen.
8.4's ability to pull up appendrel members with non-Var outputs exposes the
fact that we need to work harder here.  Per gripe from Sergey Burladyan.

src/backend/optimizer/path/allpaths.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/optimizer/path/allpaths.c,v 1.183 2009/06/11 14:48:58 momjian Exp $
+ *	  $PostgreSQL: pgsql/src/backend/optimizer/path/allpaths.c,v 1.184 2009/07/06 18:26:30 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -29,6 +29,7 @@
 #include "optimizer/plancat.h"
 #include "optimizer/planner.h"
 #include "optimizer/prep.h"
+#include "optimizer/restrictinfo.h"
 #include "optimizer/var.h"
 #include "parser/parse_clause.h"
 #include "parser/parsetree.h"
@@ -318,6 +319,8 @@ set_append_rel_pathlist(PlannerInfo *root, RelOptInfo *rel,
 		int			childRTindex;
 		RangeTblEntry *childRTE;
 		RelOptInfo *childrel;
+		List	   *childquals;
+		Node	   *childqual;
 		Path	   *childpath;
 		ListCell   *parentvars;
 		ListCell   *childvars;
@@ -342,10 +345,34 @@ set_append_rel_pathlist(PlannerInfo *root, RelOptInfo *rel,
 		 * baserestrictinfo quals are needed before we can check for
 		 * constraint exclusion; so do that first and then check to see if we
 		 * can disregard this child.
+		 *
+		 * As of 8.4, the child rel's targetlist might contain non-Var
+		 * expressions, which means that substitution into the quals
+		 * could produce opportunities for const-simplification, and perhaps
+		 * even pseudoconstant quals.  To deal with this, we strip the
+		 * RestrictInfo nodes, do the substitution, do const-simplification,
+		 * and then reconstitute the RestrictInfo layer.
 		 */
-		childrel->baserestrictinfo = (List *)
-			adjust_appendrel_attrs((Node *) rel->baserestrictinfo,
-								   appinfo);
+		childquals = get_all_actual_clauses(rel->baserestrictinfo);
+		childquals = (List *) adjust_appendrel_attrs((Node *) childquals,
+													 appinfo);
+		childqual = eval_const_expressions(root, (Node *)
+										   make_ands_explicit(childquals));
+		if (childqual && IsA(childqual, Const) &&
+			(((Const *) childqual)->constisnull ||
+			 !DatumGetBool(((Const *) childqual)->constvalue)))
+		{
+			/*
+			 * Restriction reduces to constant FALSE or constant NULL after
+			 * substitution, so this child need not be scanned.
+			 */
+			set_dummy_rel_pathlist(childrel);
+			continue;
+		}
+		childquals = make_ands_implicit((Expr *) childqual);
+		childquals = make_restrictinfos_from_actual_clauses(root,
+															childquals);
+		childrel->baserestrictinfo = childquals;
 
 		if (relation_excluded_by_constraints(root, childrel, childRTE))
 		{

src/backend/optimizer/prep/prepunion.c

@@ -22,7 +22,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/optimizer/prep/prepunion.c,v 1.171 2009/06/11 14:48:59 momjian Exp $
+ *	  $PostgreSQL: pgsql/src/backend/optimizer/prep/prepunion.c,v 1.172 2009/07/06 18:26:30 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -1636,57 +1636,7 @@ adjust_appendrel_attrs_mutator(Node *node, AppendRelInfo *context)
 	Assert(!IsA(node, SpecialJoinInfo));
 	Assert(!IsA(node, AppendRelInfo));
 	Assert(!IsA(node, PlaceHolderInfo));
-
-	/*
-	 * We have to process RestrictInfo nodes specially.
-	 */
-	if (IsA(node, RestrictInfo))
-	{
-		RestrictInfo *oldinfo = (RestrictInfo *) node;
-		RestrictInfo *newinfo = makeNode(RestrictInfo);
-
-		/* Copy all flat-copiable fields */
-		memcpy(newinfo, oldinfo, sizeof(RestrictInfo));
-
-		/* Recursively fix the clause itself */
-		newinfo->clause = (Expr *)
-			adjust_appendrel_attrs_mutator((Node *) oldinfo->clause, context);
-
-		/* and the modified version, if an OR clause */
-		newinfo->orclause = (Expr *)
-			adjust_appendrel_attrs_mutator((Node *) oldinfo->orclause, context);
-
-		/* adjust relid sets too */
-		newinfo->clause_relids = adjust_relid_set(oldinfo->clause_relids,
-												  context->parent_relid,
-												  context->child_relid);
-		newinfo->required_relids = adjust_relid_set(oldinfo->required_relids,
-													context->parent_relid,
-													context->child_relid);
-		newinfo->left_relids = adjust_relid_set(oldinfo->left_relids,
-												context->parent_relid,
-												context->child_relid);
-		newinfo->right_relids = adjust_relid_set(oldinfo->right_relids,
-												 context->parent_relid,
-												 context->child_relid);
-
-		/*
-		 * Reset cached derivative fields, since these might need to have
-		 * different values when considering the child relation.
-		 */
-		newinfo->eval_cost.startup = -1;
-		newinfo->norm_selec = -1;
-		newinfo->outer_selec = -1;
-		newinfo->left_ec = NULL;
-		newinfo->right_ec = NULL;
-		newinfo->left_em = NULL;
-		newinfo->right_em = NULL;
-		newinfo->scansel_cache = NIL;
-		newinfo->left_bucketsize = -1;
-		newinfo->right_bucketsize = -1;
-
-		return (Node *) newinfo;
-	}
+	Assert(!IsA(node, RestrictInfo));
 
 	/*
 	 * NOTE: we do not need to recurse into sublinks, because they should

src/backend/optimizer/util/restrictinfo.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/optimizer/util/restrictinfo.c,v 1.60 2009/06/11 14:48:59 momjian Exp $
+ *	  $PostgreSQL: pgsql/src/backend/optimizer/util/restrictinfo.c,v 1.61 2009/07/06 18:26:30 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -271,6 +271,57 @@ make_restrictinfo_from_bitmapqual(Path *bitmapqual,
 	return result;
 }
 
+/*
+ * make_restrictinfos_from_actual_clauses
+ *
+ * Given a list of implicitly-ANDed restriction clauses, produce a list
+ * of RestrictInfo nodes.  This is used to reconstitute the RestrictInfo
+ * representation after doing transformations of a list of clauses.
+ *
+ * We assume that the clauses are relation-level restrictions and therefore
+ * we don't have to worry about is_pushed_down, outerjoin_delayed, or
+ * nullable_relids (these can be assumed true, false, and NULL, respectively).
+ * We do take care to recognize pseudoconstant clauses properly.
+ */
+List *
+make_restrictinfos_from_actual_clauses(PlannerInfo *root,
+									   List *clause_list)
+{
+	List	   *result = NIL;
+	ListCell   *l;
+
+	foreach(l, clause_list)
+	{
+		Expr   *clause = (Expr *) lfirst(l);
+		bool	pseudoconstant;
+		RestrictInfo *rinfo;
+
+		/*
+		 * It's pseudoconstant if it contains no Vars and no volatile
+		 * functions.  We probably can't see any sublinks here, so
+		 * contain_var_clause() would likely be enough, but for safety
+		 * use contain_vars_of_level() instead.
+		 */
+		pseudoconstant =
+			!contain_vars_of_level((Node *) clause, 0) &&
+			!contain_volatile_functions((Node *) clause);
+		if (pseudoconstant)
+		{
+			/* tell createplan.c to check for gating quals */
+			root->hasPseudoConstantQuals = true;
+		}
+
+		rinfo = make_restrictinfo(clause,
+								  true,
+								  false,
+								  pseudoconstant,
+								  NULL,
+								  NULL);
+		result = lappend(result, rinfo);
+	}
+	return result;
+}
+
 /*
  * make_restrictinfo_internal
  *
@@ -481,6 +532,31 @@ get_actual_clauses(List *restrictinfo_list)
 	return result;
 }
 
+/*
+ * get_all_actual_clauses
+ *
+ * Returns a list containing the bare clauses from 'restrictinfo_list'.
+ *
+ * This loses the distinction between regular and pseudoconstant clauses,
+ * so be careful what you use it for.
+ */
+List *
+get_all_actual_clauses(List *restrictinfo_list)
+{
+	List	   *result = NIL;
+	ListCell   *l;
+
+	foreach(l, restrictinfo_list)
+	{
+		RestrictInfo *rinfo = (RestrictInfo *) lfirst(l);
+
+		Assert(IsA(rinfo, RestrictInfo));
+
+		result = lappend(result, rinfo->clause);
+	}
+	return result;
+}
+
 /*
  * extract_actual_clauses
  *

src/include/optimizer/restrictinfo.h

@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1996-2009, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/include/optimizer/restrictinfo.h,v 1.44 2009/05/09 22:51:41 tgl Exp $
+ * $PostgreSQL: pgsql/src/include/optimizer/restrictinfo.h,v 1.45 2009/07/06 18:26:30 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -30,8 +30,11 @@ extern RestrictInfo *make_restrictinfo(Expr *clause,
 extern List *make_restrictinfo_from_bitmapqual(Path *bitmapqual,
 								  bool is_pushed_down,
 								  bool include_predicates);
+extern List *make_restrictinfos_from_actual_clauses(PlannerInfo *root,
+									   List *clause_list);
 extern bool restriction_is_or_clause(RestrictInfo *restrictinfo);
 extern List *get_actual_clauses(List *restrictinfo_list);
+extern List *get_all_actual_clauses(List *restrictinfo_list);
 extern List *extract_actual_clauses(List *restrictinfo_list,
 					   bool pseudoconstant);
 extern void extract_actual_join_clauses(List *restrictinfo_list,