Add ability to fetch the restrictions per relation

With this commit, we add the ability to add restrictions
per relation. We simply rely on the restrictions that Postgres
keeps per relation.

src/backend/distributed/planner/relation_restriction_equivalence.c

@@ -26,9 +26,13 @@
 #include "nodes/primnodes.h"
 #if PG_VERSION_NUM >= PG_VERSION_12
 #include "nodes/pathnodes.h"
+#include "optimizer/optimizer.h"
 #else
+#include "optimizer/cost.h"
 #include "nodes/relation.h"
 #endif
+#include "optimizer/paths.h"
+#include "optimizer/var.h"
 #include "parser/parsetree.h"
 #include "optimizer/pathnode.h"
 
@@ -139,6 +143,7 @@ static Index RelationRestrictionPartitionKeyIndex(RelationRestriction *
 												  relationRestriction);
 static bool AllRelationsInRestrictionContextColocated(RelationRestrictionContext *
 													  restrictionContext);
+static bool IsParam(Node *node);
 static RelationRestrictionContext * FilterRelationRestrictionContext(
 	RelationRestrictionContext *relationRestrictionContext,
 	Relids
@@ -1832,6 +1837,101 @@ FilterPlannerRestrictionForQuery(PlannerRestrictionContext *plannerRestrictionCo
 }
 
 
+/*
+ * GetRestrictInfoListForRelation gets a range table entry and planner
+ * restriction context. The function returns a list of expressions that
+ * appear in the restriction context for only the given relation. And,
+ * all the varnos are set to 1.
+ */
+List *
+GetRestrictInfoListForRelation(RangeTblEntry *rangeTblEntry,
+							   PlannerRestrictionContext *plannerRestrictionContext)
+{
+	int rteIdentity = GetRTEIdentity(rangeTblEntry);
+	RelationRestrictionContext *relationRestrictionContext =
+		plannerRestrictionContext->relationRestrictionContext;
+	Relids queryRteIdentities = bms_make_singleton(rteIdentity);
+	RelationRestrictionContext *filteredRelationRestrictionContext =
+		FilterRelationRestrictionContext(relationRestrictionContext, queryRteIdentities);
+	List *filteredRelationRestrictionList =
+		filteredRelationRestrictionContext->relationRestrictionList;
+
+	if (list_length(filteredRelationRestrictionList) != 1)
+	{
+		return NIL;
+	}
+
+	RelationRestriction *relationRestriction =
+		(RelationRestriction *) linitial(filteredRelationRestrictionList);
+
+	RelOptInfo *relOptInfo = relationRestriction->relOptInfo;
+	List *baseRestrictInfo = relOptInfo->baserestrictinfo;
+
+	List *restrictExprList = NIL;
+	ListCell *restrictCell = NULL;
+	foreach(restrictCell, baseRestrictInfo)
+	{
+		RestrictInfo *restrictInfo = (RestrictInfo *) lfirst(restrictCell);
+		Expr *restrictionClause = restrictInfo->clause;
+		List *varClauses = NIL;
+		ListCell *varClauseCell = NULL;
+		Relids varnos = NULL;
+
+		Expr *copyOfRestrictClause = NULL;
+
+		/* we cannot process Params beacuse they are not known at this point */
+		if (FindNodeCheck((Node *) restrictionClause, IsParam))
+		{
+			continue;
+		}
+
+		/*
+		 * If the restriction involves multiple tables, we cannot add it to
+		 * input relation's expression list.
+		 */
+		varnos = pull_varnos((Node *) restrictionClause);
+		if (bms_num_members(varnos) != 1)
+		{
+			continue;
+		}
+
+		/*
+		 * We're going to add this restriction expression to a subquery
+		 * which consists of only one relation in its jointree. Thus,
+		 * simply set the varnos accordingly.
+		 */
+		copyOfRestrictClause = (Expr *) copyObject((Node *) restrictionClause);
+		varClauses = pull_var_clause_default((Node *) copyOfRestrictClause);
+		foreach(varClauseCell, varClauses)
+		{
+			Var *column = (Var *) lfirst(varClauseCell);
+
+			column->varno = 1;
+			column->varnoold = 1;
+		}
+
+		restrictExprList = lappend(restrictExprList, copyOfRestrictClause);
+	}
+
+	return restrictExprList;
+}
+
+
+/*
+ * IsParam determines whether the given node is a param.
+ */
+static bool
+IsParam(Node *node)
+{
+	if (IsA(node, Param))
+	{
+		return true;
+	}
+
+	return false;
+}
+
+
 /*
  * FilterRelationRestrictionContext gets a relation restriction context and
  * set of rte identities. It returns the relation restrictions that that appear

src/include/distributed/relation_restriction_equivalence.h

@@ -36,6 +36,12 @@ extern List * DistributedRelationIdList(Query *query);
 extern PlannerRestrictionContext * FilterPlannerRestrictionForQuery(
 	PlannerRestrictionContext *plannerRestrictionContext,
 	Query *query);
+extern List * GetRestrictInfoListForRelation(RangeTblEntry *rangeTblEntry,
+											 PlannerRestrictionContext *
+											 plannerRestrictionContext);
+extern JoinRestrictionContext * RemoveDuplicateJoinRestrictions(JoinRestrictionContext *
+																joinRestrictionContext);
+
 extern bool EquivalenceListContainsRelationsEquality(List *attributeEquivalenceList,
 													 RelationRestrictionContext *
 													 restrictionContext);