Add a reverse-translation column number array to struct AppendRelInfo.

This provides for cheaper mapping of child columns back to parent
columns.  The one existing use-case in examine_simple_variable()
would hardly justify this by itself; but an upcoming bug fix will
make use of this array in a mainstream code path, and it seems
likely that we'll find other uses for it as we continue to build
out the partitioning infrastructure.

Discussion: https://postgr.es/m/12424.1575168015@sss.pgh.pa.us

src/backend/nodes/copyfuncs.c

@@ -2327,6 +2327,8 @@ _copyAppendRelInfo(const AppendRelInfo *from)
 	COPY_SCALAR_FIELD(parent_reltype);
 	COPY_SCALAR_FIELD(child_reltype);
 	COPY_NODE_FIELD(translated_vars);
+	COPY_SCALAR_FIELD(num_child_cols);
+	COPY_POINTER_FIELD(parent_colnos, from->num_child_cols * sizeof(AttrNumber));
 	COPY_SCALAR_FIELD(parent_reloid);
 
 	return newnode;

src/backend/nodes/equalfuncs.c

@@ -900,6 +900,8 @@ _equalAppendRelInfo(const AppendRelInfo *a, const AppendRelInfo *b)
 	COMPARE_SCALAR_FIELD(parent_reltype);
 	COMPARE_SCALAR_FIELD(child_reltype);
 	COMPARE_NODE_FIELD(translated_vars);
+	COMPARE_SCALAR_FIELD(num_child_cols);
+	COMPARE_POINTER_FIELD(parent_colnos, a->num_child_cols * sizeof(AttrNumber));
 	COMPARE_SCALAR_FIELD(parent_reloid);
 
 	return true;

src/backend/nodes/nodeFuncs.c

@@ -3103,6 +3103,7 @@ expression_tree_mutator(Node *node,
 
 				FLATCOPY(newnode, appinfo, AppendRelInfo);
 				MUTATE(newnode->translated_vars, appinfo->translated_vars, List *);
+				/* Assume nothing need be done with parent_colnos[] */
 				return (Node *) newnode;
 			}
 			break;

src/backend/nodes/outfuncs.c

@@ -2509,6 +2509,8 @@ _outAppendRelInfo(StringInfo str, const AppendRelInfo *node)
 	WRITE_OID_FIELD(parent_reltype);
 	WRITE_OID_FIELD(child_reltype);
 	WRITE_NODE_FIELD(translated_vars);
+	WRITE_INT_FIELD(num_child_cols);
+	WRITE_ATTRNUMBER_ARRAY(parent_colnos, node->num_child_cols);
 	WRITE_OID_FIELD(parent_reloid);
 }
 

src/backend/optimizer/prep/prepjointree.c

@@ -81,7 +81,7 @@ static void pull_up_union_leaf_queries(Node *setOp, PlannerInfo *root,
 									   int parentRTindex, Query *setOpQuery,
 									   int childRToffset);
 static void make_setop_translation_list(Query *query, Index newvarno,
-										List **translated_vars);
+										AppendRelInfo *appinfo);
 static bool is_simple_subquery(Query *subquery, RangeTblEntry *rte,
 							   JoinExpr *lowest_outer_join);
 static Node *pull_up_simple_values(PlannerInfo *root, Node *jtnode,
@@ -1313,8 +1313,7 @@ pull_up_union_leaf_queries(Node *setOp, PlannerInfo *root, int parentRTindex,
 		appinfo->child_relid = childRTindex;
 		appinfo->parent_reltype = InvalidOid;
 		appinfo->child_reltype = InvalidOid;
-		make_setop_translation_list(setOpQuery, childRTindex,
-									&appinfo->translated_vars);
+		make_setop_translation_list(setOpQuery, childRTindex, appinfo);
 		appinfo->parent_reloid = InvalidOid;
 		root->append_rel_list = lappend(root->append_rel_list, appinfo);
 
@@ -1356,14 +1355,22 @@ pull_up_union_leaf_queries(Node *setOp, PlannerInfo *root, int parentRTindex,
  *	  a UNION ALL member.  (At this point it's just a simple list of
  *	  referencing Vars, but if we succeed in pulling up the member
  *	  subquery, the Vars will get replaced by pulled-up expressions.)
+ *	  Also create the rather trivial reverse-translation array.
  */
 static void
 make_setop_translation_list(Query *query, Index newvarno,
-							List **translated_vars)
+							AppendRelInfo *appinfo)
 {
 	List	   *vars = NIL;
+	AttrNumber *pcolnos;
 	ListCell   *l;
 
+	/* Initialize reverse-translation array with all entries zero */
+	/* (entries for resjunk columns will stay that way) */
+	appinfo->num_child_cols = list_length(query->targetList);
+	appinfo->parent_colnos = pcolnos =
+		(AttrNumber *) palloc0(appinfo->num_child_cols * sizeof(AttrNumber));
+
 	foreach(l, query->targetList)
 	{
 		TargetEntry *tle = (TargetEntry *) lfirst(l);
@@ -1372,9 +1379,10 @@ make_setop_translation_list(Query *query, Index newvarno,
 			continue;
 
 		vars = lappend(vars, makeVarFromTargetEntry(newvarno, tle));
+		pcolnos[tle->resno - 1] = tle->resno;
 	}
 
-	*translated_vars = vars;
+	appinfo->translated_vars = vars;
 }
 
 /*

src/backend/optimizer/util/appendinfo.c

@@ -34,7 +34,7 @@ typedef struct
 static void make_inh_translation_list(Relation oldrelation,
 									  Relation newrelation,
 									  Index newvarno,
-									  List **translated_vars);
+									  AppendRelInfo *appinfo);
 static Node *adjust_appendrel_attrs_mutator(Node *node,
 											adjust_appendrel_attrs_context *context);
 static List *adjust_inherited_tlist(List *tlist,
@@ -55,8 +55,7 @@ make_append_rel_info(Relation parentrel, Relation childrel,
 	appinfo->child_relid = childRTindex;
 	appinfo->parent_reltype = parentrel->rd_rel->reltype;
 	appinfo->child_reltype = childrel->rd_rel->reltype;
-	make_inh_translation_list(parentrel, childrel, childRTindex,
-							  &appinfo->translated_vars);
+	make_inh_translation_list(parentrel, childrel, childRTindex, appinfo);
 	appinfo->parent_reloid = RelationGetRelid(parentrel);
 
 	return appinfo;
@@ -65,16 +64,23 @@ make_append_rel_info(Relation parentrel, Relation childrel,
 /*
  * make_inh_translation_list
  *	  Build the list of translations from parent Vars to child Vars for
- *	  an inheritance child.
+ *	  an inheritance child, as well as a reverse-translation array.
+ *
+ * The reverse-translation array has an entry for each child relation
+ * column, which is either the 1-based index of the corresponding parent
+ * column, or 0 if there's no match (that happens for dropped child columns,
+ * as well as child columns beyond those of the parent, which are allowed in
+ * traditional inheritance though not partitioning).
  *
  * For paranoia's sake, we match type/collation as well as attribute name.
  */
 static void
 make_inh_translation_list(Relation oldrelation, Relation newrelation,
 						  Index newvarno,
-						  List **translated_vars)
+						  AppendRelInfo *appinfo)
 {
 	List	   *vars = NIL;
+	AttrNumber *pcolnos;
 	TupleDesc	old_tupdesc = RelationGetDescr(oldrelation);
 	TupleDesc	new_tupdesc = RelationGetDescr(newrelation);
 	Oid			new_relid = RelationGetRelid(newrelation);
@@ -83,6 +89,11 @@ make_inh_translation_list(Relation oldrelation, Relation newrelation,
 	int			old_attno;
 	int			new_attno = 0;
 
+	/* Initialize reverse-translation array with all entries zero */
+	appinfo->num_child_cols = newnatts;
+	appinfo->parent_colnos = pcolnos =
+		(AttrNumber *) palloc0(newnatts * sizeof(AttrNumber));
+
 	for (old_attno = 0; old_attno < oldnatts; old_attno++)
 	{
 		Form_pg_attribute att;
@@ -115,6 +126,7 @@ make_inh_translation_list(Relation oldrelation, Relation newrelation,
 										 atttypmod,
 										 attcollation,
 										 0));
+			pcolnos[old_attno] = old_attno + 1;
 			continue;
 		}
 
@@ -138,6 +150,7 @@ make_inh_translation_list(Relation oldrelation, Relation newrelation,
 				elog(ERROR, "could not find inherited attribute \"%s\" of relation \"%s\"",
 					 attname, RelationGetRelationName(newrelation));
 			new_attno = ((Form_pg_attribute) GETSTRUCT(newtup))->attnum - 1;
+			Assert(new_attno >= 0 && new_attno < newnatts);
 			ReleaseSysCache(newtup);
 
 			att = TupleDescAttr(new_tupdesc, new_attno);
@@ -157,10 +170,11 @@ make_inh_translation_list(Relation oldrelation, Relation newrelation,
 									 atttypmod,
 									 attcollation,
 									 0));
+		pcolnos[new_attno] = old_attno + 1;
 		new_attno++;
 	}
 
-	*translated_vars = vars;
+	appinfo->translated_vars = vars;
 }
 
 /*

src/backend/utils/adt/selfuncs.c

@@ -4769,29 +4769,17 @@ examine_simple_variable(PlannerInfo *root, Var *var,
 										root)->rtekind == RTE_RELATION)
 				{
 					int			parent_varattno;
-					ListCell   *l;
 
-					parent_varattno = 1;
 					found = false;
-					foreach(l, appinfo->translated_vars)
-					{
-						Var		   *childvar = lfirst_node(Var, l);
-
-						/* Ignore dropped attributes of the parent. */
-						if (childvar != NULL &&
-							varattno == childvar->varattno)
-						{
-							found = true;
-							break;
-						}
-						parent_varattno++;
-					}
-
-					if (!found)
-						break;
+					if (varattno <= 0 || varattno > appinfo->num_child_cols)
+						break;	/* safety check */
+					parent_varattno = appinfo->parent_colnos[varattno - 1];
+					if (parent_varattno == 0)
+						break;	/* Var is local to child */
 
 					varno = appinfo->parent_relid;
 					varattno = parent_varattno;
+					found = true;
 
 					/* If the parent is itself a child, continue up. */
 					appinfo = root->append_rel_array[varno];

src/include/nodes/pathnodes.h

@@ -2151,17 +2151,13 @@ struct SpecialJoinInfo
  * "append relation" (essentially, a list of child RTEs), we build an
  * AppendRelInfo for each child RTE.  The list of AppendRelInfos indicates
  * which child RTEs must be included when expanding the parent, and each node
- * carries information needed to translate Vars referencing the parent into
- * Vars referencing that child.
- *
- * These structs are kept in the PlannerInfo node's append_rel_list.
- * Note that we just throw all the structs into one list, and scan the
- * whole list when desiring to expand any one parent.  We could have used
- * a more complex data structure (eg, one list per parent), but this would
- * be harder to update during operations such as pulling up subqueries,
- * and not really any easier to scan.  Considering that typical queries
- * will not have many different append parents, it doesn't seem worthwhile
- * to complicate things.
+ * carries information needed to translate between columns of the parent and
+ * columns of the child.
+ *
+ * These structs are kept in the PlannerInfo node's append_rel_list, with
+ * append_rel_array[] providing a convenient lookup method for the struct
+ * associated with a particular child relid (there can be only one, though
+ * parent rels may have many entries in append_rel_list).
  *
  * Note: after completion of the planner prep phase, any given RTE is an
  * append parent having entries in append_rel_list if and only if its
@@ -2218,6 +2214,15 @@ typedef struct AppendRelInfo
 	 */
 	List	   *translated_vars;	/* Expressions in the child's Vars */
 
+	/*
+	 * This array simplifies translations in the reverse direction, from
+	 * child's column numbers to parent's.  The entry at [ccolno - 1] is the
+	 * 1-based parent column number for child column ccolno, or zero if that
+	 * child column is dropped or doesn't exist in the parent.
+	 */
+	int			num_child_cols; /* length of array */
+	AttrNumber *parent_colnos;	/* array of parent attnos, or zeroes */
+
 	/*
 	 * We store the parent table's OID here for inheritance, or InvalidOid for
 	 * UNION ALL.  This is only needed to help in generating error messages if