Removing INNER JOINs

diff --git a/src/backend/commands/trigger.c b/src/backend/commands/trigger.c
index ebccfea..ea26615 100644
--- a/src/backend/commands/trigger.c
+++ b/src/backend/commands/trigger.c
@@ -3889,6 +3889,17 @@ afterTriggerInvokeEvents(AfterTriggerEventList *events,
 	return all_fired;
 }
 
+/* ----------
+ * AfterTriggerQueueIsEmpty()
+ *
+ *	True if there are no pending triggers in the queue.
+ * ----------
+ */
+bool
+AfterTriggerQueueIsEmpty(void)
+{
+	return (afterTriggers.query_depth == -1 && afterTriggers.events.head == NULL);
+}
 
 /* ----------
  * AfterTriggerBeginXact()
diff --git a/src/backend/executor/execProcnode.c b/src/backend/executor/execProcnode.c
index e27c062..59dd3f3 100644
--- a/src/backend/executor/execProcnode.c
+++ b/src/backend/executor/execProcnode.c
@@ -77,6 +77,7 @@
  */
 #include "postgres.h"
 
+#include "commands/trigger.h"
 #include "executor/executor.h"
 #include "executor/nodeAgg.h"
 #include "executor/nodeAppend.h"
@@ -115,6 +116,24 @@
 #include "miscadmin.h"
 
 
+/* FIXME: this needs moved into the correct place */
+PlanState *
+ExecInitAlternativePlan(AlternativePlan *node, EState *estate, int eflags)
+{
+	/*
+	 * FIXME: this is not very robust, it would be better to store some flags
+	 * somewhere to indicate which plan is suitable for which purpose. For now
+	 * this is ok as we only generate a maximum of 2 plans, and the all purpose
+	 * plan is always the 2nd on in the list. Here we simply just initialze the
+	 * correct plan and return the plan state from the root node of that plan,
+	 * this completely eliminates the alternative plan node from the plan and
+	 * it should be never seen by EXPLAIN or EXPLAIN ANALYZE.
+	 */
+	if (!AfterTriggerQueueIsEmpty())
+		return (PlanState *) ExecInitNode((Plan *) list_nth(node->planList, 1), estate, eflags);
+	else
+		return (PlanState *) ExecInitNode((Plan *) linitial(node->planList), estate, eflags);
+}
 /* ------------------------------------------------------------------------
  *		ExecInitNode
  *
@@ -147,6 +166,11 @@ ExecInitNode(Plan *node, EState *estate, int eflags)
 			/*
 			 * control nodes
 			 */
+		case T_AlternativePlan:
+			result = (PlanState *) ExecInitAlternativePlan((AlternativePlan *)node,
+												  estate, eflags);
+			break;
+
 		case T_Result:
 			result = (PlanState *) ExecInitResult((Result *) node,
 												  estate, eflags);
diff --git a/src/backend/nodes/copyfuncs.c b/src/backend/nodes/copyfuncs.c
index 6b1bf7b..8bc9bf2 100644
--- a/src/backend/nodes/copyfuncs.c
+++ b/src/backend/nodes/copyfuncs.c
@@ -93,6 +93,7 @@ _copyPlannedStmt(const PlannedStmt *from)
 	COPY_NODE_FIELD(relationOids);
 	COPY_NODE_FIELD(invalItems);
 	COPY_SCALAR_FIELD(nParamExec);
+	COPY_SCALAR_FIELD(suitableFor);
 
 	return newnode;
 }
@@ -963,6 +964,16 @@ _copyLimit(const Limit *from)
 	return newnode;
 }
 
+static AlternativePlan *
+_copyAlternativePlan(const AlternativePlan *from)
+{
+	AlternativePlan *newnode = makeNode(AlternativePlan);
+
+	COPY_NODE_FIELD(planList);
+
+	return newnode;
+}
+
 /*
  * _copyNestLoopParam
  */
@@ -4118,6 +4129,9 @@ copyObject(const void *from)
 		case T_Limit:
 			retval = _copyLimit(from);
 			break;
+		case T_AlternativePlan:
+			retval = _copyAlternativePlan(from);
+			break;
 		case T_NestLoopParam:
 			retval = _copyNestLoopParam(from);
 			break;
diff --git a/src/backend/nodes/outfuncs.c b/src/backend/nodes/outfuncs.c
index edbd09f..b3af253 100644
--- a/src/backend/nodes/outfuncs.c
+++ b/src/backend/nodes/outfuncs.c
@@ -255,6 +255,7 @@ _outPlannedStmt(StringInfo str, const PlannedStmt *node)
 	WRITE_NODE_FIELD(relationOids);
 	WRITE_NODE_FIELD(invalItems);
 	WRITE_INT_FIELD(nParamExec);
+	WRITE_INT_FIELD(suitableFor);
 }
 
 /*
@@ -1716,6 +1717,7 @@ _outPlannerGlobal(StringInfo str, const PlannerGlobal *node)
 	WRITE_UINT_FIELD(lastPHId);
 	WRITE_UINT_FIELD(lastRowMarkId);
 	WRITE_BOOL_FIELD(transientPlan);
+	WRITE_INT_FIELD(suitableFor);
 }
 
 static void
@@ -1801,6 +1803,7 @@ _outRelOptInfo(StringInfo str, const RelOptInfo *node)
 	/* we don't try to print fdwroutine or fdw_private */
 	WRITE_NODE_FIELD(baserestrictinfo);
 	WRITE_NODE_FIELD(joininfo);
+	WRITE_INT_FIELD(skipFlags);
 	WRITE_BOOL_FIELD(has_eclass_joins);
 }
 
diff --git a/src/backend/optimizer/path/allpaths.c b/src/backend/optimizer/path/allpaths.c
index 449fdc3..3b6d51d 100644
--- a/src/backend/optimizer/path/allpaths.c
+++ b/src/backend/optimizer/path/allpaths.c
@@ -97,7 +97,8 @@ static void set_cte_pathlist(PlannerInfo *root, RelOptInfo *rel,
 				 RangeTblEntry *rte);
 static void set_worktable_pathlist(PlannerInfo *root, RelOptInfo *rel,
 					   RangeTblEntry *rte);
-static RelOptInfo *make_rel_from_joinlist(PlannerInfo *root, List *joinlist);
+static RelOptInfo *make_rel_from_joinlist(PlannerInfo *root, List *joinlist,
+					   int skipflags);
 static bool subquery_is_pushdown_safe(Query *subquery, Query *topquery,
 						  pushdown_safety_info *safetyInfo);
 static bool recurse_pushdown_safe(Node *setOp, Query *topquery,
@@ -122,7 +123,7 @@ static void remove_unused_subquery_outputs(Query *subquery, RelOptInfo *rel);
  *	  single rel that represents the join of all base rels in the query.
  */
 RelOptInfo *
-make_one_rel(PlannerInfo *root, List *joinlist)
+make_one_rel(PlannerInfo *root, List *joinlist, int skipflags)
 {
 	RelOptInfo *rel;
 	Index		rti;
@@ -142,7 +143,8 @@ make_one_rel(PlannerInfo *root, List *joinlist)
 		Assert(brel->relid == rti);		/* sanity check on array */
 
 		/* ignore RTEs that are "other rels" */
-		if (brel->reloptkind != RELOPT_BASEREL)
+		if (brel->reloptkind != RELOPT_BASEREL ||
+			brel->skipFlags & skipflags)
 			continue;
 
 		root->all_baserels = bms_add_member(root->all_baserels, brel->relid);
@@ -157,12 +159,13 @@ make_one_rel(PlannerInfo *root, List *joinlist)
 	/*
 	 * Generate access paths for the entire join tree.
 	 */
-	rel = make_rel_from_joinlist(root, joinlist);
+	rel = make_rel_from_joinlist(root, joinlist, skipflags);
+
 
 	/*
 	 * The result should join all and only the query's base rels.
 	 */
-	Assert(bms_equal(rel->relids, root->all_baserels));
+	Assert(bms_is_subset(root->all_baserels, rel->relids));
 
 	return rel;
 }
@@ -1496,7 +1499,7 @@ set_worktable_pathlist(PlannerInfo *root, RelOptInfo *rel, RangeTblEntry *rte)
  * data structure.
  */
 static RelOptInfo *
-make_rel_from_joinlist(PlannerInfo *root, List *joinlist)
+make_rel_from_joinlist(PlannerInfo *root, List *joinlist, int skipflags)
 {
 	int			levels_needed;
 	List	   *initial_rels;
@@ -1528,11 +1531,22 @@ make_rel_from_joinlist(PlannerInfo *root, List *joinlist)
 			int			varno = ((RangeTblRef *) jlnode)->rtindex;
 
 			thisrel = find_base_rel(root, varno);
+
+			/*
+			 * if this relation can be skipped for these skipflags, then we'll
+			 * not bother including this in the list of relations to join to
+			 */
+			if ((thisrel->skipFlags & skipflags))
+			{
+				/* one less level needed too */
+				levels_needed--;
+				continue;
+			}
 		}
 		else if (IsA(jlnode, List))
 		{
 			/* Recurse to handle subproblem */
-			thisrel = make_rel_from_joinlist(root, (List *) jlnode);
+			thisrel = make_rel_from_joinlist(root, (List *) jlnode, skipflags);
 		}
 		else
 		{
diff --git a/src/backend/optimizer/path/equivclass.c b/src/backend/optimizer/path/equivclass.c
index 9919d27..33f8a90 100644
--- a/src/backend/optimizer/path/equivclass.c
+++ b/src/backend/optimizer/path/equivclass.c
@@ -49,8 +49,6 @@ static List *generate_join_implied_equalities_broken(PlannerInfo *root,
 										Relids outer_relids,
 										Relids nominal_inner_relids,
 										RelOptInfo *inner_rel);
-static Oid select_equality_operator(EquivalenceClass *ec,
-						 Oid lefttype, Oid righttype);
 static RestrictInfo *create_join_clause(PlannerInfo *root,
 				   EquivalenceClass *ec, Oid opno,
 				   EquivalenceMember *leftem,
@@ -1282,7 +1280,7 @@ generate_join_implied_equalities_broken(PlannerInfo *root,
  *
  * Returns InvalidOid if no operator can be found for this datatype combination
  */
-static Oid
+Oid
 select_equality_operator(EquivalenceClass *ec, Oid lefttype, Oid righttype)
 {
 	ListCell   *lc;
diff --git a/src/backend/optimizer/plan/analyzejoins.c b/src/backend/optimizer/plan/analyzejoins.c
index e99d416..df0d42f 100644
--- a/src/backend/optimizer/plan/analyzejoins.c
+++ b/src/backend/optimizer/plan/analyzejoins.c
@@ -32,13 +32,21 @@
 #include "utils/lsyscache.h"
 
 /* local functions */
-static bool join_is_removable(PlannerInfo *root, SpecialJoinInfo *sjinfo);
+static bool innerjoin_is_removable(PlannerInfo *root, List *joinlist,
+					  RangeTblRef *removalrtr, Relids ignoredrels);
+static bool leftjoin_is_removable(PlannerInfo *root, SpecialJoinInfo *sjinfo);
+static bool relation_is_needed(PlannerInfo *root, Relids joinrelids,
+					  RelOptInfo *rel, Relids ignoredrels);
+static bool relation_has_foreign_key_for(PlannerInfo *root, RelOptInfo *rel,
+					  RelOptInfo *referencedrel, List *referencing_vars,
+					  List *index_vars, List *operator_list);
+static bool expressions_match_foreign_key(ForeignKeyInfo *fk, List *fkvars,
+					  List *indexvars, List *operators);
 static void remove_rel_from_query(PlannerInfo *root, int relid,
 					  Relids joinrelids);
 static List *remove_rel_from_joinlist(List *joinlist, int relid, int *nremoved);
 static Oid	distinct_col_search(int colno, List *colnos, List *opids);
 
-
 /*
  * remove_useless_joins
  *		Check for relations that don't actually need to be joined at all,
@@ -46,26 +54,101 @@ static Oid	distinct_col_search(int colno, List *colnos, List *opids);
  *
  * We are passed the current joinlist and return the updated list.  Other
  * data structures that have to be updated are accessible via "root".
+ *
+ * There are 2 methods here for removing joins. Joins such as LEFT JOINs
+ * which can be proved to be needless due to lack of use of any of the joining
+ * relation's columns and the existence of a unique index on a subset of the
+ * join clause, can simply be removed from the query plan at plan time. For
+ * certain other join types we make use of foreign keys to attempt to prove the
+ * join is needless, though, for these we're unable to be certain that the join
+ * is not required at plan time, as if the plan is executed when pending
+ * foreign key triggers have not yet been fired, then the foreign key is
+ * effectively violated until these triggers have fired. Removing a join in
+ * such a case could cause a query to produce incorrect results.
+ *
+ * Instead we handle this case by marking the RangeTblEntry for the relation
+ * with a special flag which tells the executor that it's possible that joining
+ * to this relation may not be required. The executor may then check this flag
+ * and choose to skip the join based on if there are foreign key triggers
+ * pending or not.
  */
 List *
 remove_useless_joins(PlannerInfo *root, List *joinlist)
 {
 	ListCell   *lc;
+	Relids		removedrels = NULL;
 
 	/*
-	 * We are only interested in relations that are left-joined to, so we can
-	 * scan the join_info_list to find them easily.
+	 * Start by analyzing INNER JOINed relations in order to determine if any
+	 * of the relations can be ignored.
 	 */
 restart:
+	foreach(lc, joinlist)
+	{
+		RangeTblRef		*rtr = (RangeTblRef *) lfirst(lc);
+		RelOptInfo		*rel;
+
+		if (!IsA(rtr, RangeTblRef))
+			continue;
+
+		rel = root->simple_rel_array[rtr->rtindex];
+
+		/* Don't try to remove this one again if we've already removed it */
+		if ((rel->skipFlags & PLAN_SUITABILITY_FK_TRIGGER_EMPTY) != 0)
+			continue;
+
+		/* skip if the join can't be removed */
+		if (!innerjoin_is_removable(root, joinlist, rtr, removedrels))
+			continue;
+
+		/*
+		 * Since we're not actually removing the join here, we need to maintain
+		 * a list of relations that we've "removed" so when we're checking if
+		 * other relations can be removed we'll know that if the to be removed
+		 * relation is only referenced by a relation that we've already removed
+		 * that it can be safely assumed that the relation is not referenced by
+		 * any useful relation.
+		 */
+		removedrels = bms_add_member(removedrels, rtr->rtindex);
+
+		/*
+		 * Mark that this relation is only required when the foreign key trigger
+		 * queue us non-empty.
+		 */
+		rel->skipFlags |= PLAN_SUITABILITY_FK_TRIGGER_EMPTY;
+
+		/*
+		 * Globally mark the plan to say it has skippable nodes. This lets
+		 * the executor know if it should bother trying to pull the joins
+		 * out of the plan tree
+		 */
+		root->glob->suitableFor |= PLAN_SUITABILITY_FK_TRIGGER_EMPTY;
+
+		/*
+		 * Restart the scan.  This is necessary to ensure we find all removable
+		 * joins independently of their ordering. (note that since we've added
+		 * this relation to the removedrels, we may now realize that other
+		 * relations can also be removed as they're only referenced by the one
+		 * that we've just marked as possibly removable).
+		 */
+		goto restart;
+	}
+
+	/* now process special joins. Currently only left joins are supported */
 	foreach(lc, root->join_info_list)
 	{
 		SpecialJoinInfo *sjinfo = (SpecialJoinInfo *) lfirst(lc);
 		int			innerrelid;
 		int			nremoved;
 
-		/* Skip if not removable */
-		if (!join_is_removable(root, sjinfo))
-			continue;
+		if (sjinfo->jointype == JOIN_LEFT)
+		{
+			/* Skip if not removable */
+			if (!leftjoin_is_removable(root, sjinfo))
+				continue;
+		}
+		else
+			continue; /* we don't support this join type */
 
 		/*
 		 * Currently, join_is_removable can only succeed when the sjinfo's
@@ -91,12 +174,11 @@ restart:
 		root->join_info_list = list_delete_ptr(root->join_info_list, sjinfo);
 
 		/*
-		 * Restart the scan.  This is necessary to ensure we find all
-		 * removable joins independently of ordering of the join_info_list
-		 * (note that removal of attr_needed bits may make a join appear
-		 * removable that did not before).  Also, since we just deleted the
-		 * current list cell, we'd have to have some kluge to continue the
-		 * list scan anyway.
+		 * Restart the scan.  This is necessary to ensure we find all removable
+		 * joins independently of their ordering. (note that removal of
+		 * attr_needed bits may make a join, inner or outer, appear removable
+		 * that did not before).   Also, since we just deleted the current list
+		 * cell, we'd have to have some kluge to continue the list scan anyway.
 		 */
 		goto restart;
 	}
@@ -136,8 +218,213 @@ clause_sides_match_join(RestrictInfo *rinfo, Relids outerrelids,
 }
 
 /*
- * join_is_removable
- *	  Check whether we need not perform this special join at all, because
+ * innerjoin_is_removable
+ *		True if the join to removalrtr can be removed.
+ *
+ * In order to prove a relation which is inner joined is not required we must
+ * be sure that the join would emit exactly 1 row on the join condition. This
+ * differs from the logic which is used for proving LEFT JOINs can be removed,
+ * where it's possible to just check that a unique index exists on the relation
+ * being removed which has a set of columns that is a subset of the columns
+ * seen in the join condition. If no matching row is found then left join would
+ * not remove the non-matched row from the result set. This is not the case
+ * with INNER JOINs, so here we must use foreign keys as proof that the 1 row
+ * exists before we can allow any joins to be removed.
+ */
+static bool
+innerjoin_is_removable(PlannerInfo *root, List *joinlist,
+					   RangeTblRef *removalrtr, Relids ignoredrels)
+{
+	ListCell   *lc;
+	RelOptInfo *removalrel;
+
+	removalrel = find_base_rel(root, removalrtr->rtindex);
+
+	/*
+	 * As foreign keys may only reference base rels which have unique indexes,
+	 * we needn't go any further if we're not dealing with a base rel, or if
+	 * the base rel has no unique indexes. We'd also better abort if the
+	 * rtekind is anything but a relation, as things like sub-queries may have
+	 * grouping or distinct clauses that would cause us not to be able to use
+	 * the foreign key to prove the existence of a row matching the join
+	 * condition. We also abort if the rel has no eclass joins as such a rel
+	 * could well be joined using some operator which is not an equality
+	 * operator, or the rel may not even be inner joined at all.
+	 *
+	 * Here we actually only check if the rel has any indexes, ideally we'd be
+	 * checking for unique indexes, but we could only determine that by looping
+	 * over the indexlist, and this is likely too expensive a check to be worth
+	 * it here.
+	 */
+	if (removalrel->reloptkind != RELOPT_BASEREL ||
+		removalrel->rtekind != RTE_RELATION ||
+		removalrel->has_eclass_joins == false ||
+		removalrel->indexlist == NIL)
+		return false;
+
+	/*
+	 * Currently we disallow the removal if we find any baserestrictinfo items
+	 * on the relation being removed. The reason for this is that these would
+	 * filter out rows and make it so the foreign key cannot prove that we'll
+	 * match exactly 1 row on the join condition. However, this check is
+	 * currently probably a bit overly strict as it should be possible to just
+	 * check and ensure that each Var seen in the baserestrictinfo is also
+	 * present in an eclass and if so, just translate and move the whole
+	 * baserestrictinfo over to the relation which has the foreign key to prove
+	 * that this join is not needed. e.g:
+	 * SELECT a.* FROM a INNER JOIN b ON a.b_id = b.id WHERE b.id = 1;
+	 * could become: SELECT a.* FROM a WHERE a.b_id = 1;
+	 */
+	if (removalrel->baserestrictinfo != NIL)
+		return false;
+
+	/*
+	 * Currently only eclass joins are supported, so if there are any non
+	 * eclass join quals then we'll report the join is non-removable.
+	 */
+	if (removalrel->joininfo != NIL)
+		return false;
+
+	/*
+	 * Now we'll search through each relation in the joinlist to see if we can
+	 * find a relation which has a foreign key which references removalrel on
+	 * the join condition. If we find a rel with a foreign key which matches
+	 * the join condition exactly, then we can be sure that exactly 1 row will
+	 * be matched on the join, if we also see that no Vars from the relation
+	 * are needed, then we can report the join as removable.
+	 */
+	foreach (lc, joinlist)
+	{
+		RangeTblRef	*rtr = (RangeTblRef *) lfirst(lc);
+		RelOptInfo	*rel;
+		ListCell	*lc2;
+		List		*referencing_vars;
+		List		*index_vars;
+		List		*operator_list;
+		Relids		 joinrelids;
+
+		/* we can't remove ourself, or anything other than RangeTblRefs */
+		if (rtr == removalrtr || !IsA(rtr, RangeTblRef))
+			continue;
+
+		rel = find_base_rel(root, rtr->rtindex);
+
+		/*
+		 * The only relation type that can help us is a base rel with at least
+		 * one foreign key defined, if there's no eclass joins then this rel
+		 * is not going to help us prove the removalrel is not needed.
+		 */
+		if (rel->reloptkind != RELOPT_BASEREL ||
+			rel->rtekind != RTE_RELATION ||
+			rel->has_eclass_joins == false ||
+			rel->fklist == NIL)
+			continue;
+
+		/*
+		 * Both rels have eclass joins, but do they have eclass joins to each
+		 * other? Skip this rel if it does not.
+		 */
+		if (!have_relevant_eclass_joinclause(root, rel, removalrel))
+			continue;
+
+		joinrelids = bms_union(rel->relids, removalrel->relids);
+
+		/* if any of the Vars from the relation are needed then abort */
+		if (relation_is_needed(root, joinrelids, removalrel, ignoredrels))
+			return false;
+
+		referencing_vars = NIL;
+		index_vars = NIL;
+		operator_list = NIL;
+
+		/* now populate the lists with the join condition Vars */
+		foreach(lc2, root->eq_classes)
+		{
+			EquivalenceClass *ec = (EquivalenceClass *) lfirst(lc2);
+
+			if (list_length(ec->ec_members) <= 1)
+				continue;
+
+			if (bms_overlap(removalrel->relids, ec->ec_relids) &&
+				bms_overlap(rel->relids, ec->ec_relids))
+			{
+				ListCell *lc3;
+				Var *refvar = NULL;
+				Var *idxvar = NULL;
+
+				/*
+				 * Look at each member of the eclass and try to find a Var from
+				 * each side of the join that we can append to the list of
+				 * columns that should be checked against each foreign key.
+				 *
+				 * The following logic does not allow for join removals to take
+				 * place for foreign keys that have duplicate columns on the
+				 * referencing side of the foreign key, such as:
+				 * (a,a) references (x,y)
+				 * The use case for such a foreign key is likely small enough
+				 * that we needn't bother making this code anymore complex to
+				 * solve. If we find more than 1 Var from any of the rels then
+				 * we'll bail out.
+				 */
+				foreach (lc3, ec->ec_members)
+				{
+					EquivalenceMember *ecm = (EquivalenceMember *) lfirst(lc3);
+
+					Var *var = (Var *) ecm->em_expr;
+
+					if (!IsA(var, Var))
+						continue; /* Ignore Consts */
+
+					if (var->varno == rel->relid)
+					{
+						if (refvar != NULL)
+							return false;
+						refvar = var;
+					}
+
+					else if (var->varno == removalrel->relid)
+					{
+						if (idxvar != NULL)
+							return false;
+						idxvar = var;
+					}
+				}
+
+				if (refvar != NULL && idxvar != NULL)
+				{
+					Oid opno;
+					Oid reloid = root->simple_rte_array[refvar->varno]->relid;
+
+					if (!get_attnotnull(reloid, refvar->varattno))
+						return false;
+
+					/* grab the correct equality operator for these two vars */
+					opno = select_equality_operator(ec, refvar->vartype, idxvar->vartype);
+
+					if (!OidIsValid(opno))
+						return false;
+
+					referencing_vars = lappend(referencing_vars, refvar);
+					index_vars = lappend(index_vars, idxvar);
+					operator_list = lappend_oid(operator_list, opno);
+				}
+			}
+		}
+
+		if (referencing_vars != NULL)
+		{
+			if (relation_has_foreign_key_for(root, rel, removalrel,
+				referencing_vars, index_vars, operator_list))
+				return true; /* removalrel can be removed */
+		}
+	}
+
+	return false; /* can't remove join */
+}
+
+/*
+ * leftjoin_is_removable
+ *	  Check whether we need not perform this left join at all, because
  *	  it will just duplicate its left input.
  *
  * This is true for a left join for which the join condition cannot match
@@ -147,7 +434,7 @@ clause_sides_match_join(RestrictInfo *rinfo, Relids outerrelids,
  * above the join.
  */
 static bool
-join_is_removable(PlannerInfo *root, SpecialJoinInfo *sjinfo)
+leftjoin_is_removable(PlannerInfo *root, SpecialJoinInfo *sjinfo)
 {
 	int			innerrelid;
 	RelOptInfo *innerrel;
@@ -155,14 +442,14 @@ join_is_removable(PlannerInfo *root, SpecialJoinInfo *sjinfo)
 	Relids		joinrelids;
 	List	   *clause_list = NIL;
 	ListCell   *l;
-	int			attroff;
+
+	Assert(sjinfo->jointype == JOIN_LEFT);
 
 	/*
-	 * Must be a non-delaying left join to a single baserel, else we aren't
+	 * Must be a non-delaying join to a single baserel, else we aren't
 	 * going to be able to do anything with it.
 	 */
-	if (sjinfo->jointype != JOIN_LEFT ||
-		sjinfo->delay_upper_joins)
+	if (sjinfo->delay_upper_joins)
 		return false;
 
 	if (!bms_get_singleton_member(sjinfo->min_righthand, &innerrelid))
@@ -206,52 +493,9 @@ join_is_removable(PlannerInfo *root, SpecialJoinInfo *sjinfo)
 	/* Compute the relid set for the join we are considering */
 	joinrelids = bms_union(sjinfo->min_lefthand, sjinfo->min_righthand);
 
-	/*
-	 * We can't remove the join if any inner-rel attributes are used above the
-	 * join.
-	 *
-	 * Note that this test only detects use of inner-rel attributes in higher
-	 * join conditions and the target list.  There might be such attributes in
-	 * pushed-down conditions at this join, too.  We check that case below.
-	 *
-	 * As a micro-optimization, it seems better to start with max_attr and
-	 * count down rather than starting with min_attr and counting up, on the
-	 * theory that the system attributes are somewhat less likely to be wanted
-	 * and should be tested last.
-	 */
-	for (attroff = innerrel->max_attr - innerrel->min_attr;
-		 attroff >= 0;
-		 attroff--)
-	{
-		if (!bms_is_subset(innerrel->attr_needed[attroff], joinrelids))
-			return false;
-	}
-
-	/*
-	 * Similarly check that the inner rel isn't needed by any PlaceHolderVars
-	 * that will be used above the join.  We only need to fail if such a PHV
-	 * actually references some inner-rel attributes; but the correct check
-	 * for that is relatively expensive, so we first check against ph_eval_at,
-	 * which must mention the inner rel if the PHV uses any inner-rel attrs as
-	 * non-lateral references.  Note that if the PHV's syntactic scope is just
-	 * the inner rel, we can't drop the rel even if the PHV is variable-free.
-	 */
-	foreach(l, root->placeholder_list)
-	{
-		PlaceHolderInfo *phinfo = (PlaceHolderInfo *) lfirst(l);
-
-		if (bms_is_subset(phinfo->ph_needed, joinrelids))
-			continue;			/* PHV is not used above the join */
-		if (bms_overlap(phinfo->ph_lateral, innerrel->relids))
-			return false;		/* it references innerrel laterally */
-		if (!bms_overlap(phinfo->ph_eval_at, innerrel->relids))
-			continue;			/* it definitely doesn't reference innerrel */
-		if (bms_is_subset(phinfo->ph_eval_at, innerrel->relids))
-			return false;		/* there isn't any other place to eval PHV */
-		if (bms_overlap(pull_varnos((Node *) phinfo->ph_var->phexpr),
-						innerrel->relids))
-			return false;		/* it does reference innerrel */
-	}
+	/* if the relation is referenced in the query then it cannot be removed */
+	if (relation_is_needed(root, joinrelids, innerrel, NULL))
+		return false;
 
 	/*
 	 * Search for mergejoinable clauses that constrain the inner rel against
@@ -368,6 +612,218 @@ join_is_removable(PlannerInfo *root, SpecialJoinInfo *sjinfo)
 	return false;
 }
 
+/*
+ * relation_is_needed
+ *		True if any of the Vars from this relation are required in the query
+ */
+static inline bool
+relation_is_needed(PlannerInfo *root, Relids joinrelids, RelOptInfo *rel, Relids ignoredrels)
+{
+	int		  attroff;
+	ListCell *l;
+
+	/*
+	 * rel is referenced if any of it's attributes are used above the join.
+	 *
+	 * Note that this test only detects use of rel's attributes in higher
+	 * join conditions and the target list.  There might be such attributes in
+	 * pushed-down conditions at this join, too.  We check that case below.
+	 *
+	 * As a micro-optimization, it seems better to start with max_attr and
+	 * count down rather than starting with min_attr and counting up, on the
+	 * theory that the system attributes are somewhat less likely to be wanted
+	 * and should be tested last.
+	 */
+	for (attroff = rel->max_attr - rel->min_attr;
+		 attroff >= 0;
+		 attroff--)
+	{
+		if (!bms_is_subset(bms_difference(rel->attr_needed[attroff], ignoredrels), joinrelids))
+			return true;
+	}
+
+	/*
+	 * Similarly check that rel isn't needed by any PlaceHolderVars that will
+	 * be used above the join.  We only need to fail if such a PHV actually
+	 * references some of rel's attributes; but the correct check for that is
+	 * relatively expensive, so we first check against ph_eval_at, which must
+	 * mention rel if the PHV uses any of-rel's attrs as non-lateral
+	 * references.  Note that if the PHV's syntactic scope is just rel, we
+	 * can't return true even if the PHV is variable-free.
+	 */
+	foreach(l, root->placeholder_list)
+	{
+		PlaceHolderInfo *phinfo = (PlaceHolderInfo *) lfirst(l);
+
+		if (bms_is_subset(phinfo->ph_needed, joinrelids))
+			continue;			/* PHV is not used above the join */
+		if (bms_overlap(phinfo->ph_lateral, rel->relids))
+			return true;		/* it references rel laterally */
+		if (!bms_overlap(phinfo->ph_eval_at, rel->relids))
+			continue;			/* it definitely doesn't reference rel */
+		if (bms_is_subset(phinfo->ph_eval_at, rel->relids))
+			return true;		/* there isn't any other place to eval PHV */
+		if (bms_overlap(pull_varnos((Node *) phinfo->ph_var->phexpr),
+						rel->relids))
+			return true;		/* it does reference rel */
+	}
+
+	return false; /* it does not reference rel */
+}
+
+/*
+ * relation_has_foreign_key_for
+ *	  Checks if rel has a foreign key which references referencedrel with the
+ *	  given list of expressions.
+ *
+ *	For the match to succeed:
+ *	  referencing_vars must match the columns defined in the foreign key.
+ *	  index_vars must match the columns defined in the index for the foreign key.
+ */
+static bool
+relation_has_foreign_key_for(PlannerInfo *root, RelOptInfo *rel,
+			RelOptInfo *referencedrel, List *referencing_vars,
+			List *index_vars, List *operator_list)
+{
+	ListCell *lc;
+	Oid		  refreloid;
+
+	/*
+	 * Look up the Oid of the referenced relation. We only want to look at
+	 * foreign keys on the referencing relation which reference this relation.
+	 */
+	refreloid = root->simple_rte_array[referencedrel->relid]->relid;
+
+	Assert(list_length(referencing_vars) > 0);
+	Assert(list_length(referencing_vars) == list_length(index_vars));
+	Assert(list_length(referencing_vars) == list_length(operator_list));
+
+	/*
+	 * Search through each foreign key on the referencing relation and try
+	 * to find one which references the relation in the join condition. If we
+	 * find one then we'll send the join conditions off to
+	 * expressions_match_foreign_key() to see if they match the foreign key.
+	 */
+	foreach(lc, rel->fklist)
+	{
+		ForeignKeyInfo *fk = (ForeignKeyInfo *) lfirst(lc);
+
+		if (fk->confrelid == refreloid)
+		{
+			if (expressions_match_foreign_key(fk, referencing_vars,
+				index_vars, operator_list))
+				return true;
+		}
+	}
+
+	return false;
+}
+
+/*
+ * expressions_match_foreign_key
+ *		True if the given fkvars, indexvars and operators will match
+ *		exactly 1 record in the referenced relation of the foreign key.
+ *
+ * Note: This function expects fkvars and indexvars to only contain Var types.
+ *		 Expression indexes are not supported by foreign keys.
+ */
+static bool
+expressions_match_foreign_key(ForeignKeyInfo *fk, List *fkvars,
+					List *indexvars, List *operators)
+{
+	ListCell  *lc;
+	ListCell  *lc2;
+	ListCell  *lc3;
+	Bitmapset *allitems;
+	Bitmapset *matcheditems;
+	int		   lstidx;
+	int		   col;
+
+	Assert(list_length(fkvars) == list_length(indexvars));
+	Assert(list_length(fkvars) == list_length(operators));
+
+	/*
+	 * Fast path out if there's not enough conditions to match each column in
+	 * the foreign key. Note that we cannot check that the number of
+	 * expressions are equal here since it would cause any expressions which
+	 * are duplicated not to match.
+	 */
+	if (list_length(fkvars) < fk->conncols)
+		return false;
+
+	/*
+	 * We need to ensure that each foreign key column can be matched to a list
+	 * item, and we need to ensure that each list item can be matched to a
+	 * foreign key column. We do this by looping over each foreign key column
+	 * and checking that we can find an item in the list which matches the
+	 * current column, however this method does not allow us to ensure that no
+	 * additional items exist in the list. We could solve that by performing
+	 * another loop over each list item and check that it matches a foreign key
+	 * column, but that's a bit wasteful. Instead we'll use 2 bitmapsets, one
+	 * to store the 0 based index of each list item, and with the other we'll
+	 * store each list index that we've managed to match. After we're done
+	 * matching we'll just make sure that both bitmapsets are equal.
+	 */
+	allitems = NULL;
+	matcheditems = NULL;
+
+	/*
+	 * Build a bitmapset which contains each 1 based list index. It seems more
+	 * efficient to do this in reverse so that we allocate enough memory for
+	 * the bitmapset on first loop rather than reallocating each time we find
+	 * we need a bit more space.
+	 */
+	for (lstidx = list_length(fkvars) - 1; lstidx >= 0; lstidx--)
+		allitems = bms_add_member(allitems, lstidx);
+
+	for (col = 0; col < fk->conncols; col++)
+	{
+		bool  matched = false;
+
+		lstidx = 0;
+
+		forthree(lc, fkvars, lc2, indexvars, lc3, operators)
+		{
+			Var *expr = (Var *) lfirst(lc);
+			Var *idxexpr = (Var *) lfirst(lc2);
+			Oid  opr = lfirst_oid(lc3);
+
+			Assert(IsA(expr, Var));
+			Assert(IsA(idxexpr, Var));
+
+			/* Does this join qual match up to the current fkey column? */
+			if (fk->conkey[col] == expr->varattno &&
+				fk->confkey[col] == idxexpr->varattno &&
+				equality_ops_are_compatible(opr, fk->conpfeqop[col]))
+			{
+				matched = true;
+
+				/* mark this list item as matched */
+				matcheditems = bms_add_member(matcheditems, lstidx);
+
+				/*
+				 * Don't break here as there may be duplicate expressions
+				 * that we also need to match against.
+				 */
+			}
+			lstidx++;
+		}
+
+		/* punt if there's no match. */
+		if (!matched)
+			return false;
+	}
+
+	/*
+	 * Ensure that we managed to match every item in the list to a foreign key
+	 * column.
+	 */
+	if (!bms_equal(allitems, matcheditems))
+		return false;
+
+	return true; /* matched */
+}
+
 
 /*
  * Remove the target relid from the planner's data structures, having
diff --git a/src/backend/optimizer/plan/createplan.c b/src/backend/optimizer/plan/createplan.c
index bf8dbe0..19333e6 100644
--- a/src/backend/optimizer/plan/createplan.c
+++ b/src/backend/optimizer/plan/createplan.c
@@ -4675,6 +4675,15 @@ make_lockrows(Plan *lefttree, List *rowMarks, int epqParam)
 	return node;
 }
 
+AlternativePlan *
+make_alternativeplan(List *planlist)
+{
+	AlternativePlan *node = makeNode(AlternativePlan);
+	node->planList = planlist;
+
+	return node;
+}
+
 /*
  * Note: offset_est and count_est are passed in to save having to repeat
  * work already done to estimate the values of the limitOffset and limitCount
diff --git a/src/backend/optimizer/plan/planagg.c b/src/backend/optimizer/plan/planagg.c
index 94ca92d..866e0c5 100644
--- a/src/backend/optimizer/plan/planagg.c
+++ b/src/backend/optimizer/plan/planagg.c
@@ -409,6 +409,7 @@ build_minmax_path(PlannerInfo *root, MinMaxAggInfo *mminfo,
 	Path	   *sorted_path;
 	Cost		path_cost;
 	double		path_fraction;
+	List	   *final_rel_list;
 
 	/*----------
 	 * Generate modified query of the form
@@ -478,8 +479,12 @@ build_minmax_path(PlannerInfo *root, MinMaxAggInfo *mminfo,
 	subroot->tuple_fraction = 1.0;
 	subroot->limit_tuples = 1.0;
 
-	final_rel = query_planner(subroot, parse->targetList,
-							  minmax_qp_callback, NULL);
+	final_rel_list = query_planner(subroot, parse->targetList,
+							  minmax_qp_callback, NULL, false);
+
+	Assert(list_length(final_rel_list) ==  1);
+
+	final_rel = (RelOptInfo *) linitial(final_rel_list);
 
 	/*
 	 * Get the best presorted path, that being the one that's cheapest for
diff --git a/src/backend/optimizer/plan/planmain.c b/src/backend/optimizer/plan/planmain.c
index 93484a0..964371f 100644
--- a/src/backend/optimizer/plan/planmain.c
+++ b/src/backend/optimizer/plan/planmain.c
@@ -51,15 +51,17 @@
  * qp_callback once we have completed merging the query's equivalence classes.
  * (We cannot construct canonical pathkeys until that's done.)
  */
-RelOptInfo *
+List *
 query_planner(PlannerInfo *root, List *tlist,
-			  query_pathkeys_callback qp_callback, void *qp_extra)
+			  query_pathkeys_callback qp_callback, void *qp_extra,
+			  bool alternativePlans)
 {
 	Query	   *parse = root->parse;
 	List	   *joinlist;
 	RelOptInfo *final_rel;
 	Index		rti;
 	double		total_pages;
+	List	   *finalrellist = NIL;
 
 	/*
 	 * If the query has an empty join tree, then it's something easy like
@@ -84,7 +86,7 @@ query_planner(PlannerInfo *root, List *tlist,
 		root->canon_pathkeys = NIL;
 		(*qp_callback) (root, qp_extra);
 
-		return final_rel;
+		return lappend(NIL, final_rel);
 	}
 
 	/*
@@ -231,14 +233,33 @@ query_planner(PlannerInfo *root, List *tlist,
 	root->total_table_pages = total_pages;
 
 	/*
-	 * Ready to do the primary planning.
+	 * if we've marked some join types are removable then since we won't know
+	 * until execution time if the relations can be removed, then we'd better
+	 * generate both plans and leave it up to the executor which one gets used
 	 */
-	final_rel = make_one_rel(root, joinlist);
+	if (root->glob->suitableFor != PLAN_SUITABILITY_ALL_PURPOSE
+		&& alternativePlans == true)
+	{
+		/* Generate fully optimized plan, with all removable joins removed */
+		final_rel = make_one_rel(root, joinlist, root->glob->suitableFor);
+
+		/* Check that we got at least one usable path */
+		if (!final_rel || !final_rel->cheapest_total_path ||
+			final_rel->cheapest_total_path->param_info != NULL)
+			elog(ERROR, "failed to construct the join relation");
+
+		finalrellist = lappend(finalrellist, final_rel);
+	}
+
+	/* generate an all purpose plan */
+	final_rel = make_one_rel(root, joinlist, PLAN_SUITABILITY_ALL_PURPOSE);
 
 	/* Check that we got at least one usable path */
 	if (!final_rel || !final_rel->cheapest_total_path ||
 		final_rel->cheapest_total_path->param_info != NULL)
 		elog(ERROR, "failed to construct the join relation");
 
-	return final_rel;
+	finalrellist = lappend(finalrellist, final_rel);
+
+	return finalrellist;
 }
diff --git a/src/backend/optimizer/plan/planner.c b/src/backend/optimizer/plan/planner.c
index f752ecc..c8f3a3e 100644
--- a/src/backend/optimizer/plan/planner.c
+++ b/src/backend/optimizer/plan/planner.c
@@ -178,6 +178,7 @@ standard_planner(Query *parse, int cursorOptions, ParamListInfo boundParams)
 	glob->lastRowMarkId = 0;
 	glob->transientPlan = false;
 	glob->hasRowSecurity = false;
+	glob->suitableFor = PLAN_SUITABILITY_ALL_PURPOSE;
 
 	/* Determine what fraction of the plan is likely to be scanned */
 	if (cursorOptions & CURSOR_OPT_FAST_PLAN)
@@ -256,6 +257,7 @@ standard_planner(Query *parse, int cursorOptions, ParamListInfo boundParams)
 	result->invalItems = glob->invalItems;
 	result->nParamExec = glob->nParamExec;
 	result->hasRowSecurity = glob->hasRowSecurity;
+	result->suitableFor = glob->suitableFor;
 
 	return result;
 }
@@ -1087,10 +1089,12 @@ grouping_planner(PlannerInfo *root, double tuple_fraction)
 	int64		count_est = 0;
 	double		limit_tuples = -1.0;
 	Plan	   *result_plan;
+	List	   *result_plan_list = NIL;
 	List	   *current_pathkeys;
 	double		dNumGroups = 0;
 	bool		use_hashed_distinct = false;
 	bool		tested_hashed_distinct = false;
+	ListCell   *lc;
 
 	/* Tweak caller-supplied tuple_fraction if have LIMIT/OFFSET */
 	if (parse->limitCount || parse->limitOffset)
@@ -1169,6 +1173,8 @@ grouping_planner(PlannerInfo *root, double tuple_fraction)
 		root->sort_pathkeys = make_pathkeys_for_sortclauses(root,
 															parse->sortClause,
 															tlist);
+
+		result_plan_list = lappend(NIL, result_plan);
 	}
 	else
 	{
@@ -1178,6 +1184,7 @@ grouping_planner(PlannerInfo *root, double tuple_fraction)
 		bool		need_tlist_eval = true;
 		standard_qp_extra qp_extra;
 		RelOptInfo *final_rel;
+		List	   *final_rel_list;
 		Path	   *cheapest_path;
 		Path	   *sorted_path;
 		Path	   *best_path;
@@ -1288,710 +1295,723 @@ grouping_planner(PlannerInfo *root, double tuple_fraction)
 		 * standard_qp_callback) pathkey representations of the query's sort
 		 * clause, distinct clause, etc.
 		 */
-		final_rel = query_planner(root, sub_tlist,
-								  standard_qp_callback, &qp_extra);
-
-		/*
-		 * Extract rowcount and width estimates for use below.
-		 */
-		path_rows = final_rel->rows;
-		path_width = final_rel->width;
+		final_rel_list = query_planner(root, sub_tlist,
+							  standard_qp_callback, &qp_extra, true);
 
-		/*
-		 * If there's grouping going on, estimate the number of result groups.
-		 * We couldn't do this any earlier because it depends on relation size
-		 * estimates that are created within query_planner().
-		 *
-		 * Then convert tuple_fraction to fractional form if it is absolute,
-		 * and if grouping or aggregation is involved, adjust tuple_fraction
-		 * to describe the fraction of the underlying un-aggregated tuples
-		 * that will be fetched.
-		 */
-		dNumGroups = 1;			/* in case not grouping */
-
-		if (parse->groupClause)
+		foreach(lc, final_rel_list)
 		{
-			List	   *groupExprs;
-
-			groupExprs = get_sortgrouplist_exprs(parse->groupClause,
-												 parse->targetList);
-			dNumGroups = estimate_num_groups(root, groupExprs, path_rows);
-
+			final_rel = (RelOptInfo *) lfirst(lc);
 			/*
-			 * In GROUP BY mode, an absolute LIMIT is relative to the number
-			 * of groups not the number of tuples.  If the caller gave us a
-			 * fraction, keep it as-is.  (In both cases, we are effectively
-			 * assuming that all the groups are about the same size.)
+			 * Extract rowcount and width estimates for use below.
 			 */
-			if (tuple_fraction >= 1.0)
-				tuple_fraction /= dNumGroups;
+			path_rows = final_rel->rows;
+			path_width = final_rel->width;
 
 			/*
-			 * If both GROUP BY and ORDER BY are specified, we will need two
-			 * levels of sort --- and, therefore, certainly need to read all
-			 * the tuples --- unless ORDER BY is a subset of GROUP BY.
-			 * Likewise if we have both DISTINCT and GROUP BY, or if we have a
-			 * window specification not compatible with the GROUP BY.
-			 */
-			if (!pathkeys_contained_in(root->sort_pathkeys,
-									   root->group_pathkeys) ||
-				!pathkeys_contained_in(root->distinct_pathkeys,
-									   root->group_pathkeys) ||
-				!pathkeys_contained_in(root->window_pathkeys,
-									   root->group_pathkeys))
-				tuple_fraction = 0.0;
-		}
-		else if (parse->hasAggs || root->hasHavingQual)
-		{
-			/*
-			 * Ungrouped aggregate will certainly want to read all the tuples,
-			 * and it will deliver a single result row (so leave dNumGroups
-			 * set to 1).
-			 */
-			tuple_fraction = 0.0;
-		}
-		else if (parse->distinctClause)
-		{
-			/*
-			 * Since there was no grouping or aggregation, it's reasonable to
-			 * assume the UNIQUE filter has effects comparable to GROUP BY.
-			 * (If DISTINCT is used with grouping, we ignore its effects for
-			 * rowcount estimation purposes; this amounts to assuming the
-			 * grouped rows are distinct already.)
-			 */
-			List	   *distinctExprs;
-
-			distinctExprs = get_sortgrouplist_exprs(parse->distinctClause,
-													parse->targetList);
-			dNumGroups = estimate_num_groups(root, distinctExprs, path_rows);
-
-			/*
-			 * Adjust tuple_fraction the same way as for GROUP BY, too.
-			 */
-			if (tuple_fraction >= 1.0)
-				tuple_fraction /= dNumGroups;
-		}
-		else
-		{
-			/*
-			 * Plain non-grouped, non-aggregated query: an absolute tuple
-			 * fraction can be divided by the number of tuples.
+			 * If there's grouping going on, estimate the number of result groups.
+			 * We couldn't do this any earlier because it depends on relation size
+			 * estimates that are created within query_planner().
+			 *
+			 * Then convert tuple_fraction to fractional form if it is absolute,
+			 * and if grouping or aggregation is involved, adjust tuple_fraction
+			 * to describe the fraction of the underlying un-aggregated tuples
+			 * that will be fetched.
 			 */
-			if (tuple_fraction >= 1.0)
-				tuple_fraction /= path_rows;
-		}
+			dNumGroups = 1;			/* in case not grouping */
 
-		/*
-		 * Pick out the cheapest-total path as well as the cheapest presorted
-		 * path for the requested pathkeys (if there is one).  We should take
-		 * the tuple fraction into account when selecting the cheapest
-		 * presorted path, but not when selecting the cheapest-total path,
-		 * since if we have to sort then we'll have to fetch all the tuples.
-		 * (But there's a special case: if query_pathkeys is NIL, meaning
-		 * order doesn't matter, then the "cheapest presorted" path will be
-		 * the cheapest overall for the tuple fraction.)
-		 */
-		cheapest_path = final_rel->cheapest_total_path;
-
-		sorted_path =
-			get_cheapest_fractional_path_for_pathkeys(final_rel->pathlist,
-													  root->query_pathkeys,
-													  NULL,
-													  tuple_fraction);
+			if (parse->groupClause)
+			{
+				List	   *groupExprs;
 
-		/* Don't consider same path in both guises; just wastes effort */
-		if (sorted_path == cheapest_path)
-			sorted_path = NULL;
+				groupExprs = get_sortgrouplist_exprs(parse->groupClause,
+													 parse->targetList);
+				dNumGroups = estimate_num_groups(root, groupExprs, path_rows);
 
-		/*
-		 * Forget about the presorted path if it would be cheaper to sort the
-		 * cheapest-total path.  Here we need consider only the behavior at
-		 * the tuple_fraction point.  Also, limit_tuples is only relevant if
-		 * not grouping/aggregating, so use root->limit_tuples in the
-		 * cost_sort call.
-		 */
-		if (sorted_path)
-		{
-			Path		sort_path;		/* dummy for result of cost_sort */
+				/*
+				 * In GROUP BY mode, an absolute LIMIT is relative to the number
+				 * of groups not the number of tuples.  If the caller gave us a
+				 * fraction, keep it as-is.  (In both cases, we are effectively
+				 * assuming that all the groups are about the same size.)
+				 */
+				if (tuple_fraction >= 1.0)
+					tuple_fraction /= dNumGroups;
 
-			if (root->query_pathkeys == NIL ||
-				pathkeys_contained_in(root->query_pathkeys,
-									  cheapest_path->pathkeys))
-			{
-				/* No sort needed for cheapest path */
-				sort_path.startup_cost = cheapest_path->startup_cost;
-				sort_path.total_cost = cheapest_path->total_cost;
+				/*
+				 * If both GROUP BY and ORDER BY are specified, we will need two
+				 * levels of sort --- and, therefore, certainly need to read all
+				 * the tuples --- unless ORDER BY is a subset of GROUP BY.
+				 * Likewise if we have both DISTINCT and GROUP BY, or if we have a
+				 * window specification not compatible with the GROUP BY.
+				 */
+				if (!pathkeys_contained_in(root->sort_pathkeys,
+										   root->group_pathkeys) ||
+					!pathkeys_contained_in(root->distinct_pathkeys,
+										   root->group_pathkeys) ||
+					!pathkeys_contained_in(root->window_pathkeys,
+										   root->group_pathkeys))
+					tuple_fraction = 0.0;
 			}
-			else
+			else if (parse->hasAggs || root->hasHavingQual)
 			{
-				/* Figure cost for sorting */
-				cost_sort(&sort_path, root, root->query_pathkeys,
-						  cheapest_path->total_cost,
-						  path_rows, path_width,
-						  0.0, work_mem, root->limit_tuples);
+				/*
+				 * Ungrouped aggregate will certainly want to read all the tuples,
+				 * and it will deliver a single result row (so leave dNumGroups
+				 * set to 1).
+				 */
+				tuple_fraction = 0.0;
 			}
-
-			if (compare_fractional_path_costs(sorted_path, &sort_path,
-											  tuple_fraction) > 0)
+			else if (parse->distinctClause)
 			{
-				/* Presorted path is a loser */
-				sorted_path = NULL;
-			}
-		}
+				/*
+				 * Since there was no grouping or aggregation, it's reasonable to
+				 * assume the UNIQUE filter has effects comparable to GROUP BY.
+				 * (If DISTINCT is used with grouping, we ignore its effects for
+				 * rowcount estimation purposes; this amounts to assuming the
+				 * grouped rows are distinct already.)
+				 */
+				List	   *distinctExprs;
 
-		/*
-		 * Consider whether we want to use hashing instead of sorting.
-		 */
-		if (parse->groupClause)
-		{
-			/*
-			 * If grouping, decide whether to use sorted or hashed grouping.
-			 */
-			use_hashed_grouping =
-				choose_hashed_grouping(root,
-									   tuple_fraction, limit_tuples,
-									   path_rows, path_width,
-									   cheapest_path, sorted_path,
-									   dNumGroups, &agg_costs);
-			/* Also convert # groups to long int --- but 'ware overflow! */
-			numGroups = (long) Min(dNumGroups, (double) LONG_MAX);
-		}
-		else if (parse->distinctClause && sorted_path &&
-				 !root->hasHavingQual && !parse->hasAggs && !activeWindows)
-		{
-			/*
-			 * We'll reach the DISTINCT stage without any intermediate
-			 * processing, so figure out whether we will want to hash or not
-			 * so we can choose whether to use cheapest or sorted path.
-			 */
-			use_hashed_distinct =
-				choose_hashed_distinct(root,
-									   tuple_fraction, limit_tuples,
-									   path_rows, path_width,
-									   cheapest_path->startup_cost,
-									   cheapest_path->total_cost,
-									   sorted_path->startup_cost,
-									   sorted_path->total_cost,
-									   sorted_path->pathkeys,
-									   dNumGroups);
-			tested_hashed_distinct = true;
-		}
+				distinctExprs = get_sortgrouplist_exprs(parse->distinctClause,
+														parse->targetList);
+				dNumGroups = estimate_num_groups(root, distinctExprs, path_rows);
 
-		/*
-		 * Select the best path.  If we are doing hashed grouping, we will
-		 * always read all the input tuples, so use the cheapest-total path.
-		 * Otherwise, the comparison above is correct.
-		 */
-		if (use_hashed_grouping || use_hashed_distinct || !sorted_path)
-			best_path = cheapest_path;
-		else
-			best_path = sorted_path;
+				/*
+				 * Adjust tuple_fraction the same way as for GROUP BY, too.
+				 */
+				if (tuple_fraction >= 1.0)
+					tuple_fraction /= dNumGroups;
+			}
+			else
+			{
+				/*
+				 * Plain non-grouped, non-aggregated query: an absolute tuple
+				 * fraction can be divided by the number of tuples.
+				 */
+				if (tuple_fraction >= 1.0)
+					tuple_fraction /= path_rows;
+			}
 
-		/*
-		 * Check to see if it's possible to optimize MIN/MAX aggregates. If
-		 * so, we will forget all the work we did so far to choose a "regular"
-		 * path ... but we had to do it anyway to be able to tell which way is
-		 * cheaper.
-		 */
-		result_plan = optimize_minmax_aggregates(root,
-												 tlist,
-												 &agg_costs,
-												 best_path);
-		if (result_plan != NULL)
-		{
-			/*
-			 * optimize_minmax_aggregates generated the full plan, with the
-			 * right tlist, and it has no sort order.
-			 */
-			current_pathkeys = NIL;
-		}
-		else
-		{
 			/*
-			 * Normal case --- create a plan according to query_planner's
-			 * results.
+			 * Pick out the cheapest-total path as well as the cheapest presorted
+			 * path for the requested pathkeys (if there is one).  We should take
+			 * the tuple fraction into account when selecting the cheapest
+			 * presorted path, but not when selecting the cheapest-total path,
+			 * since if we have to sort then we'll have to fetch all the tuples.
+			 * (But there's a special case: if query_pathkeys is NIL, meaning
+			 * order doesn't matter, then the "cheapest presorted" path will be
+			 * the cheapest overall for the tuple fraction.)
 			 */
-			bool		need_sort_for_grouping = false;
+			cheapest_path = final_rel->cheapest_total_path;
 
-			result_plan = create_plan(root, best_path);
-			current_pathkeys = best_path->pathkeys;
+			sorted_path =
+				get_cheapest_fractional_path_for_pathkeys(final_rel->pathlist,
+														  root->query_pathkeys,
+														  NULL,
+														  tuple_fraction);
 
-			/* Detect if we'll need an explicit sort for grouping */
-			if (parse->groupClause && !use_hashed_grouping &&
-			  !pathkeys_contained_in(root->group_pathkeys, current_pathkeys))
-			{
-				need_sort_for_grouping = true;
-
-				/*
-				 * Always override create_plan's tlist, so that we don't sort
-				 * useless data from a "physical" tlist.
-				 */
-				need_tlist_eval = true;
-			}
+			/* Don't consider same path in both guises; just wastes effort */
+			if (sorted_path == cheapest_path)
+				sorted_path = NULL;
 
 			/*
-			 * create_plan returns a plan with just a "flat" tlist of required
-			 * Vars.  Usually we need to insert the sub_tlist as the tlist of
-			 * the top plan node.  However, we can skip that if we determined
-			 * that whatever create_plan chose to return will be good enough.
+			 * Forget about the presorted path if it would be cheaper to sort the
+			 * cheapest-total path.  Here we need consider only the behavior at
+			 * the tuple_fraction point.  Also, limit_tuples is only relevant if
+			 * not grouping/aggregating, so use root->limit_tuples in the
+			 * cost_sort call.
 			 */
-			if (need_tlist_eval)
+			if (sorted_path)
 			{
-				/*
-				 * If the top-level plan node is one that cannot do expression
-				 * evaluation and its existing target list isn't already what
-				 * we need, we must insert a Result node to project the
-				 * desired tlist.
-				 */
-				if (!is_projection_capable_plan(result_plan) &&
-					!tlist_same_exprs(sub_tlist, result_plan->targetlist))
+				Path		sort_path;		/* dummy for result of cost_sort */
+
+				if (root->query_pathkeys == NIL ||
+					pathkeys_contained_in(root->query_pathkeys,
+										  cheapest_path->pathkeys))
 				{
-					result_plan = (Plan *) make_result(root,
-													   sub_tlist,
-													   NULL,
-													   result_plan);
+					/* No sort needed for cheapest path */
+					sort_path.startup_cost = cheapest_path->startup_cost;
+					sort_path.total_cost = cheapest_path->total_cost;
 				}
 				else
 				{
-					/*
-					 * Otherwise, just replace the subplan's flat tlist with
-					 * the desired tlist.
-					 */
-					result_plan->targetlist = sub_tlist;
+					/* Figure cost for sorting */
+					cost_sort(&sort_path, root, root->query_pathkeys,
+							  cheapest_path->total_cost,
+							  path_rows, path_width,
+							  0.0, work_mem, root->limit_tuples);
 				}
 
+				if (compare_fractional_path_costs(sorted_path, &sort_path,
+												  tuple_fraction) > 0)
+				{
+					/* Presorted path is a loser */
+					sorted_path = NULL;
+				}
+			}
+
+			/*
+			 * Consider whether we want to use hashing instead of sorting.
+			 */
+			if (parse->groupClause)
+			{
 				/*
-				 * Also, account for the cost of evaluation of the sub_tlist.
-				 * See comments for add_tlist_costs_to_plan() for more info.
+				 * If grouping, decide whether to use sorted or hashed grouping.
 				 */
-				add_tlist_costs_to_plan(root, result_plan, sub_tlist);
+				use_hashed_grouping =
+					choose_hashed_grouping(root,
+										   tuple_fraction, limit_tuples,
+										   path_rows, path_width,
+										   cheapest_path, sorted_path,
+										   dNumGroups, &agg_costs);
+				/* Also convert # groups to long int --- but 'ware overflow! */
+				numGroups = (long) Min(dNumGroups, (double) LONG_MAX);
 			}
-			else
+			else if (parse->distinctClause && sorted_path &&
+					 !root->hasHavingQual && !parse->hasAggs && !activeWindows)
 			{
 				/*
-				 * Since we're using create_plan's tlist and not the one
-				 * make_subplanTargetList calculated, we have to refigure any
-				 * grouping-column indexes make_subplanTargetList computed.
+				 * We'll reach the DISTINCT stage without any intermediate
+				 * processing, so figure out whether we will want to hash or not
+				 * so we can choose whether to use cheapest or sorted path.
 				 */
-				locate_grouping_columns(root, tlist, result_plan->targetlist,
-										groupColIdx);
+				use_hashed_distinct =
+					choose_hashed_distinct(root,
+										   tuple_fraction, limit_tuples,
+										   path_rows, path_width,
+										   cheapest_path->startup_cost,
+										   cheapest_path->total_cost,
+										   sorted_path->startup_cost,
+										   sorted_path->total_cost,
+										   sorted_path->pathkeys,
+										   dNumGroups);
+				tested_hashed_distinct = true;
 			}
 
 			/*
-			 * Insert AGG or GROUP node if needed, plus an explicit sort step
-			 * if necessary.
-			 *
-			 * HAVING clause, if any, becomes qual of the Agg or Group node.
+			 * Select the best path.  If we are doing hashed grouping, we will
+			 * always read all the input tuples, so use the cheapest-total path.
+			 * Otherwise, the comparison above is correct.
 			 */
-			if (use_hashed_grouping)
+			if (use_hashed_grouping || use_hashed_distinct || !sorted_path)
+				best_path = cheapest_path;
+			else
+				best_path = sorted_path;
+
+			/*
+			 * Check to see if it's possible to optimize MIN/MAX aggregates. If
+			 * so, we will forget all the work we did so far to choose a "regular"
+			 * path ... but we had to do it anyway to be able to tell which way is
+			 * cheaper.
+			 */
+			result_plan = optimize_minmax_aggregates(root,
+													 tlist,
+													 &agg_costs,
+													 best_path);
+			if (result_plan != NULL)
 			{
-				/* Hashed aggregate plan --- no sort needed */
-				result_plan = (Plan *) make_agg(root,
-												tlist,
-												(List *) parse->havingQual,
-												AGG_HASHED,
-												&agg_costs,
-												numGroupCols,
-												groupColIdx,
-									extract_grouping_ops(parse->groupClause),
-												numGroups,
-												result_plan);
-				/* Hashed aggregation produces randomly-ordered results */
+				/*
+				 * optimize_minmax_aggregates generated the full plan, with the
+				 * right tlist, and it has no sort order.
+				 */
 				current_pathkeys = NIL;
 			}
-			else if (parse->hasAggs)
+			else
 			{
-				/* Plain aggregate plan --- sort if needed */
-				AggStrategy aggstrategy;
+				/*
+				 * Normal case --- create a plan according to query_planner's
+				 * results.
+				 */
+				bool		need_sort_for_grouping = false;
+
+				result_plan = create_plan(root, best_path);
+				current_pathkeys = best_path->pathkeys;
 
-				if (parse->groupClause)
+				/* Detect if we'll need an explicit sort for grouping */
+				if (parse->groupClause && !use_hashed_grouping &&
+				  !pathkeys_contained_in(root->group_pathkeys, current_pathkeys))
 				{
-					if (need_sort_for_grouping)
+					need_sort_for_grouping = true;
+
+					/*
+					 * Always override create_plan's tlist, so that we don't sort
+					 * useless data from a "physical" tlist.
+					 */
+					need_tlist_eval = true;
+				}
+
+				/*
+				 * create_plan returns a plan with just a "flat" tlist of required
+				 * Vars.  Usually we need to insert the sub_tlist as the tlist of
+				 * the top plan node.  However, we can skip that if we determined
+				 * that whatever create_plan chose to return will be good enough.
+				 */
+				if (need_tlist_eval)
+				{
+					/*
+					 * If the top-level plan node is one that cannot do expression
+					 * evaluation and its existing target list isn't already what
+					 * we need, we must insert a Result node to project the
+					 * desired tlist.
+					 */
+					if (!is_projection_capable_plan(result_plan) &&
+						!tlist_same_exprs(sub_tlist, result_plan->targetlist))
 					{
-						result_plan = (Plan *)
-							make_sort_from_groupcols(root,
-													 parse->groupClause,
-													 groupColIdx,
-													 result_plan);
-						current_pathkeys = root->group_pathkeys;
+						result_plan = (Plan *) make_result(root,
+														   sub_tlist,
+														   NULL,
+														   result_plan);
+					}
+					else
+					{
+						/*
+						 * Otherwise, just replace the subplan's flat tlist with
+						 * the desired tlist.
+						 */
+						result_plan->targetlist = sub_tlist;
 					}
-					aggstrategy = AGG_SORTED;
 
 					/*
-					 * The AGG node will not change the sort ordering of its
-					 * groups, so current_pathkeys describes the result too.
+					 * Also, account for the cost of evaluation of the sub_tlist.
+					 * See comments for add_tlist_costs_to_plan() for more info.
 					 */
+					add_tlist_costs_to_plan(root, result_plan, sub_tlist);
 				}
 				else
 				{
-					aggstrategy = AGG_PLAIN;
-					/* Result will be only one row anyway; no sort order */
-					current_pathkeys = NIL;
+					/*
+					 * Since we're using create_plan's tlist and not the one
+					 * make_subplanTargetList calculated, we have to refigure any
+					 * grouping-column indexes make_subplanTargetList computed.
+					 */
+					locate_grouping_columns(root, tlist, result_plan->targetlist,
+											groupColIdx);
 				}
 
-				result_plan = (Plan *) make_agg(root,
-												tlist,
-												(List *) parse->havingQual,
-												aggstrategy,
-												&agg_costs,
-												numGroupCols,
-												groupColIdx,
-									extract_grouping_ops(parse->groupClause),
-												numGroups,
-												result_plan);
-			}
-			else if (parse->groupClause)
-			{
 				/*
-				 * GROUP BY without aggregation, so insert a group node (plus
-				 * the appropriate sort node, if necessary).
+				 * Insert AGG or GROUP node if needed, plus an explicit sort step
+				 * if necessary.
 				 *
-				 * Add an explicit sort if we couldn't make the path come out
-				 * the way the GROUP node needs it.
+				 * HAVING clause, if any, becomes qual of the Agg or Group node.
 				 */
-				if (need_sort_for_grouping)
+				if (use_hashed_grouping)
 				{
-					result_plan = (Plan *)
-						make_sort_from_groupcols(root,
-												 parse->groupClause,
-												 groupColIdx,
-												 result_plan);
-					current_pathkeys = root->group_pathkeys;
+					/* Hashed aggregate plan --- no sort needed */
+					result_plan = (Plan *) make_agg(root,
+													tlist,
+													(List *) parse->havingQual,
+													AGG_HASHED,
+													&agg_costs,
+													numGroupCols,
+													groupColIdx,
+										extract_grouping_ops(parse->groupClause),
+													numGroups,
+													result_plan);
+					/* Hashed aggregation produces randomly-ordered results */
+					current_pathkeys = NIL;
 				}
+				else if (parse->hasAggs)
+				{
+					/* Plain aggregate plan --- sort if needed */
+					AggStrategy aggstrategy;
 
-				result_plan = (Plan *) make_group(root,
-												  tlist,
-												  (List *) parse->havingQual,
-												  numGroupCols,
-												  groupColIdx,
-									extract_grouping_ops(parse->groupClause),
-												  dNumGroups,
-												  result_plan);
-				/* The Group node won't change sort ordering */
-			}
-			else if (root->hasHavingQual)
-			{
-				/*
-				 * No aggregates, and no GROUP BY, but we have a HAVING qual.
-				 * This is a degenerate case in which we are supposed to emit
-				 * either 0 or 1 row depending on whether HAVING succeeds.
-				 * Furthermore, there cannot be any variables in either HAVING
-				 * or the targetlist, so we actually do not need the FROM
-				 * table at all!  We can just throw away the plan-so-far and
-				 * generate a Result node.  This is a sufficiently unusual
-				 * corner case that it's not worth contorting the structure of
-				 * this routine to avoid having to generate the plan in the
-				 * first place.
-				 */
-				result_plan = (Plan *) make_result(root,
-												   tlist,
-												   parse->havingQual,
-												   NULL);
-			}
-		}						/* end of non-minmax-aggregate case */
-
-		/*
-		 * Since each window function could require a different sort order, we
-		 * stack up a WindowAgg node for each window, with sort steps between
-		 * them as needed.
-		 */
-		if (activeWindows)
-		{
-			List	   *window_tlist;
-			ListCell   *l;
+					if (parse->groupClause)
+					{
+						if (need_sort_for_grouping)
+						{
+							result_plan = (Plan *)
+								make_sort_from_groupcols(root,
+														 parse->groupClause,
+														 groupColIdx,
+														 result_plan);
+							current_pathkeys = root->group_pathkeys;
+						}
+						aggstrategy = AGG_SORTED;
+
+						/*
+						 * The AGG node will not change the sort ordering of its
+						 * groups, so current_pathkeys describes the result too.
+						 */
+					}
+					else
+					{
+						aggstrategy = AGG_PLAIN;
+						/* Result will be only one row anyway; no sort order */
+						current_pathkeys = NIL;
+					}
 
-			/*
-			 * If the top-level plan node is one that cannot do expression
-			 * evaluation, we must insert a Result node to project the desired
-			 * tlist.  (In some cases this might not really be required, but
-			 * it's not worth trying to avoid it.  In particular, think not to
-			 * skip adding the Result if the initial window_tlist matches the
-			 * top-level plan node's output, because we might change the tlist
-			 * inside the following loop.)	Note that on second and subsequent
-			 * passes through the following loop, the top-level node will be a
-			 * WindowAgg which we know can project; so we only need to check
-			 * once.
-			 */
-			if (!is_projection_capable_plan(result_plan))
-			{
-				result_plan = (Plan *) make_result(root,
-												   NIL,
-												   NULL,
-												   result_plan);
-			}
+					result_plan = (Plan *) make_agg(root,
+													tlist,
+													(List *) parse->havingQual,
+													aggstrategy,
+													&agg_costs,
+													numGroupCols,
+													groupColIdx,
+										extract_grouping_ops(parse->groupClause),
+													numGroups,
+													result_plan);
+				}
+				else if (parse->groupClause)
+				{
+					/*
+					 * GROUP BY without aggregation, so insert a group node (plus
+					 * the appropriate sort node, if necessary).
+					 *
+					 * Add an explicit sort if we couldn't make the path come out
+					 * the way the GROUP node needs it.
+					 */
+					if (need_sort_for_grouping)
+					{
+						result_plan = (Plan *)
+							make_sort_from_groupcols(root,
+													 parse->groupClause,
+													 groupColIdx,
+													 result_plan);
+						current_pathkeys = root->group_pathkeys;
+					}
 
-			/*
-			 * The "base" targetlist for all steps of the windowing process is
-			 * a flat tlist of all Vars and Aggs needed in the result.  (In
-			 * some cases we wouldn't need to propagate all of these all the
-			 * way to the top, since they might only be needed as inputs to
-			 * WindowFuncs.  It's probably not worth trying to optimize that
-			 * though.)  We also add window partitioning and sorting
-			 * expressions to the base tlist, to ensure they're computed only
-			 * once at the bottom of the stack (that's critical for volatile
-			 * functions).  As we climb up the stack, we'll add outputs for
-			 * the WindowFuncs computed at each level.
-			 */
-			window_tlist = make_windowInputTargetList(root,
+					result_plan = (Plan *) make_group(root,
 													  tlist,
-													  activeWindows);
+													  (List *) parse->havingQual,
+													  numGroupCols,
+													  groupColIdx,
+										extract_grouping_ops(parse->groupClause),
+													  dNumGroups,
+													  result_plan);
+					/* The Group node won't change sort ordering */
+				}
+				else if (root->hasHavingQual)
+				{
+					/*
+					 * No aggregates, and no GROUP BY, but we have a HAVING qual.
+					 * This is a degenerate case in which we are supposed to emit
+					 * either 0 or 1 row depending on whether HAVING succeeds.
+					 * Furthermore, there cannot be any variables in either HAVING
+					 * or the targetlist, so we actually do not need the FROM
+					 * table at all!  We can just throw away the plan-so-far and
+					 * generate a Result node.  This is a sufficiently unusual
+					 * corner case that it's not worth contorting the structure of
+					 * this routine to avoid having to generate the plan in the
+					 * first place.
+					 */
+					result_plan = (Plan *) make_result(root,
+													   tlist,
+													   parse->havingQual,
+													   NULL);
+				}
+			}						/* end of non-minmax-aggregate case */
 
 			/*
-			 * The copyObject steps here are needed to ensure that each plan
-			 * node has a separately modifiable tlist.  (XXX wouldn't a
-			 * shallow list copy do for that?)
+			 * Since each window function could require a different sort order, we
+			 * stack up a WindowAgg node for each window, with sort steps between
+			 * them as needed.
 			 */
-			result_plan->targetlist = (List *) copyObject(window_tlist);
-
-			foreach(l, activeWindows)
+			if (activeWindows)
 			{
-				WindowClause *wc = (WindowClause *) lfirst(l);
-				List	   *window_pathkeys;
-				int			partNumCols;
-				AttrNumber *partColIdx;
-				Oid		   *partOperators;
-				int			ordNumCols;
-				AttrNumber *ordColIdx;
-				Oid		   *ordOperators;
-
-				window_pathkeys = make_pathkeys_for_window(root,
-														   wc,
-														   tlist);
+				List	   *window_tlist;
+				ListCell   *l;
 
 				/*
-				 * This is a bit tricky: we build a sort node even if we don't
-				 * really have to sort.  Even when no explicit sort is needed,
-				 * we need to have suitable resjunk items added to the input
-				 * plan's tlist for any partitioning or ordering columns that
-				 * aren't plain Vars.  (In theory, make_windowInputTargetList
-				 * should have provided all such columns, but let's not assume
-				 * that here.)	Furthermore, this way we can use existing
-				 * infrastructure to identify which input columns are the
-				 * interesting ones.
+				 * If the top-level plan node is one that cannot do expression
+				 * evaluation, we must insert a Result node to project the desired
+				 * tlist.  (In some cases this might not really be required, but
+				 * it's not worth trying to avoid it.  In particular, think not to
+				 * skip adding the Result if the initial window_tlist matches the
+				 * top-level plan node's output, because we might change the tlist
+				 * inside the following loop.)	Note that on second and subsequent
+				 * passes through the following loop, the top-level node will be a
+				 * WindowAgg which we know can project; so we only need to check
+				 * once.
 				 */
-				if (window_pathkeys)
-				{
-					Sort	   *sort_plan;
-
-					sort_plan = make_sort_from_pathkeys(root,
-														result_plan,
-														window_pathkeys,
-														-1.0);
-					if (!pathkeys_contained_in(window_pathkeys,
-											   current_pathkeys))
-					{
-						/* we do indeed need to sort */
-						result_plan = (Plan *) sort_plan;
-						current_pathkeys = window_pathkeys;
-					}
-					/* In either case, extract the per-column information */
-					get_column_info_for_window(root, wc, tlist,
-											   sort_plan->numCols,
-											   sort_plan->sortColIdx,
-											   &partNumCols,
-											   &partColIdx,
-											   &partOperators,
-											   &ordNumCols,
-											   &ordColIdx,
-											   &ordOperators);
-				}
-				else
+				if (!is_projection_capable_plan(result_plan))
 				{
-					/* empty window specification, nothing to sort */
-					partNumCols = 0;
-					partColIdx = NULL;
-					partOperators = NULL;
-					ordNumCols = 0;
-					ordColIdx = NULL;
-					ordOperators = NULL;
+					result_plan = (Plan *) make_result(root,
+													   NIL,
+													   NULL,
+													   result_plan);
 				}
 
-				if (lnext(l))
-				{
-					/* Add the current WindowFuncs to the running tlist */
-					window_tlist = add_to_flat_tlist(window_tlist,
-										   wflists->windowFuncs[wc->winref]);
-				}
-				else
+				/*
+				 * The "base" targetlist for all steps of the windowing process is
+				 * a flat tlist of all Vars and Aggs needed in the result.  (In
+				 * some cases we wouldn't need to propagate all of these all the
+				 * way to the top, since they might only be needed as inputs to
+				 * WindowFuncs.  It's probably not worth trying to optimize that
+				 * though.)  We also add window partitioning and sorting
+				 * expressions to the base tlist, to ensure they're computed only
+				 * once at the bottom of the stack (that's critical for volatile
+				 * functions).  As we climb up the stack, we'll add outputs for
+				 * the WindowFuncs computed at each level.
+				 */
+				window_tlist = make_windowInputTargetList(root,
+														  tlist,
+														  activeWindows);
+
+				/*
+				 * The copyObject steps here are needed to ensure that each plan
+				 * node has a separately modifiable tlist.  (XXX wouldn't a
+				 * shallow list copy do for that?)
+				 */
+				result_plan->targetlist = (List *) copyObject(window_tlist);
+
+				foreach(l, activeWindows)
 				{
-					/* Install the original tlist in the topmost WindowAgg */
-					window_tlist = tlist;
-				}
+					WindowClause *wc = (WindowClause *) lfirst(l);
+					List	   *window_pathkeys;
+					int			partNumCols;
+					AttrNumber *partColIdx;
+					Oid		   *partOperators;
+					int			ordNumCols;
+					AttrNumber *ordColIdx;
+					Oid		   *ordOperators;
+
+					window_pathkeys = make_pathkeys_for_window(root,
+															   wc,
+															   tlist);
+
+					/*
+					 * This is a bit tricky: we build a sort node even if we don't
+					 * really have to sort.  Even when no explicit sort is needed,
+					 * we need to have suitable resjunk items added to the input
+					 * plan's tlist for any partitioning or ordering columns that
+					 * aren't plain Vars.  (In theory, make_windowInputTargetList
+					 * should have provided all such columns, but let's not assume
+					 * that here.)	Furthermore, this way we can use existing
+					 * infrastructure to identify which input columns are the
+					 * interesting ones.
+					 */
+					if (window_pathkeys)
+					{
+						Sort	   *sort_plan;
+
+						sort_plan = make_sort_from_pathkeys(root,
+															result_plan,
+															window_pathkeys,
+															-1.0);
+						if (!pathkeys_contained_in(window_pathkeys,
+												   current_pathkeys))
+						{
+							/* we do indeed need to sort */
+							result_plan = (Plan *) sort_plan;
+							current_pathkeys = window_pathkeys;
+						}
+						/* In either case, extract the per-column information */
+						get_column_info_for_window(root, wc, tlist,
+												   sort_plan->numCols,
+												   sort_plan->sortColIdx,
+												   &partNumCols,
+												   &partColIdx,
+												   &partOperators,
+												   &ordNumCols,
+												   &ordColIdx,
+												   &ordOperators);
+					}
+					else
+					{
+						/* empty window specification, nothing to sort */
+						partNumCols = 0;
+						partColIdx = NULL;
+						partOperators = NULL;
+						ordNumCols = 0;
+						ordColIdx = NULL;
+						ordOperators = NULL;
+					}
 
-				/* ... and make the WindowAgg plan node */
-				result_plan = (Plan *)
-					make_windowagg(root,
-								   (List *) copyObject(window_tlist),
-								   wflists->windowFuncs[wc->winref],
-								   wc->winref,
-								   partNumCols,
-								   partColIdx,
-								   partOperators,
-								   ordNumCols,
-								   ordColIdx,
-								   ordOperators,
-								   wc->frameOptions,
-								   wc->startOffset,
-								   wc->endOffset,
-								   result_plan);
+					if (lnext(l))
+					{
+						/* Add the current WindowFuncs to the running tlist */
+						window_tlist = add_to_flat_tlist(window_tlist,
+											   wflists->windowFuncs[wc->winref]);
+					}
+					else
+					{
+						/* Install the original tlist in the topmost WindowAgg */
+						window_tlist = tlist;
+					}
+
+					/* ... and make the WindowAgg plan node */
+					result_plan = (Plan *)
+						make_windowagg(root,
+									   (List *) copyObject(window_tlist),
+									   wflists->windowFuncs[wc->winref],
+									   wc->winref,
+									   partNumCols,
+									   partColIdx,
+									   partOperators,
+									   ordNumCols,
+									   ordColIdx,
+									   ordOperators,
+									   wc->frameOptions,
+									   wc->startOffset,
+									   wc->endOffset,
+									   result_plan);
+				}
 			}
-		}
+
+			result_plan_list = lappend(result_plan_list, result_plan);
+		}						 /* foreach final_rel_list */
 	}							/* end of if (setOperations) */
 
-	/*
-	 * If there is a DISTINCT clause, add the necessary node(s).
-	 */
-	if (parse->distinctClause)
+	foreach(lc, result_plan_list)
 	{
-		double		dNumDistinctRows;
-		long		numDistinctRows;
+		result_plan = (Plan *) lfirst(lc);
 
 		/*
-		 * If there was grouping or aggregation, use the current number of
-		 * rows as the estimated number of DISTINCT rows (ie, assume the
-		 * result was already mostly unique).  If not, use the number of
-		 * distinct-groups calculated previously.
+		 * If there is a DISTINCT clause, add the necessary node(s).
 		 */
-		if (parse->groupClause || root->hasHavingQual || parse->hasAggs)
-			dNumDistinctRows = result_plan->plan_rows;
-		else
-			dNumDistinctRows = dNumGroups;
-
-		/* Also convert to long int --- but 'ware overflow! */
-		numDistinctRows = (long) Min(dNumDistinctRows, (double) LONG_MAX);
-
-		/* Choose implementation method if we didn't already */
-		if (!tested_hashed_distinct)
+		if (parse->distinctClause)
 		{
-			/*
-			 * At this point, either hashed or sorted grouping will have to
-			 * work from result_plan, so we pass that as both "cheapest" and
-			 * "sorted".
-			 */
-			use_hashed_distinct =
-				choose_hashed_distinct(root,
-									   tuple_fraction, limit_tuples,
-									   result_plan->plan_rows,
-									   result_plan->plan_width,
-									   result_plan->startup_cost,
-									   result_plan->total_cost,
-									   result_plan->startup_cost,
-									   result_plan->total_cost,
-									   current_pathkeys,
-									   dNumDistinctRows);
-		}
+			double		dNumDistinctRows;
+			long		numDistinctRows;
 
-		if (use_hashed_distinct)
-		{
-			/* Hashed aggregate plan --- no sort needed */
-			result_plan = (Plan *) make_agg(root,
-											result_plan->targetlist,
-											NIL,
-											AGG_HASHED,
-											NULL,
-										  list_length(parse->distinctClause),
-								 extract_grouping_cols(parse->distinctClause,
-													result_plan->targetlist),
-								 extract_grouping_ops(parse->distinctClause),
-											numDistinctRows,
-											result_plan);
-			/* Hashed aggregation produces randomly-ordered results */
-			current_pathkeys = NIL;
-		}
-		else
-		{
 			/*
-			 * Use a Unique node to implement DISTINCT.  Add an explicit sort
-			 * if we couldn't make the path come out the way the Unique node
-			 * needs it.  If we do have to sort, always sort by the more
-			 * rigorous of DISTINCT and ORDER BY, to avoid a second sort
-			 * below.  However, for regular DISTINCT, don't sort now if we
-			 * don't have to --- sorting afterwards will likely be cheaper,
-			 * and also has the possibility of optimizing via LIMIT.  But for
-			 * DISTINCT ON, we *must* force the final sort now, else it won't
-			 * have the desired behavior.
+			 * If there was grouping or aggregation, use the current number of
+			 * rows as the estimated number of DISTINCT rows (ie, assume the
+			 * result was already mostly unique).  If not, use the number of
+			 * distinct-groups calculated previously.
 			 */
-			List	   *needed_pathkeys;
-
-			if (parse->hasDistinctOn &&
-				list_length(root->distinct_pathkeys) <
-				list_length(root->sort_pathkeys))
-				needed_pathkeys = root->sort_pathkeys;
+			if (parse->groupClause || root->hasHavingQual || parse->hasAggs)
+				dNumDistinctRows = result_plan->plan_rows;
 			else
-				needed_pathkeys = root->distinct_pathkeys;
+				dNumDistinctRows = dNumGroups;
+
+			/* Also convert to long int --- but 'ware overflow! */
+			numDistinctRows = (long) Min(dNumDistinctRows, (double) LONG_MAX);
+
+			/* Choose implementation method if we didn't already */
+			if (!tested_hashed_distinct)
+			{
+				/*
+				 * At this point, either hashed or sorted grouping will have to
+				 * work from result_plan, so we pass that as both "cheapest" and
+				 * "sorted".
+				 */
+				use_hashed_distinct =
+					choose_hashed_distinct(root,
+										   tuple_fraction, limit_tuples,
+										   result_plan->plan_rows,
+										   result_plan->plan_width,
+										   result_plan->startup_cost,
+										   result_plan->total_cost,
+										   result_plan->startup_cost,
+										   result_plan->total_cost,
+										   current_pathkeys,
+										   dNumDistinctRows);
+			}
 
-			if (!pathkeys_contained_in(needed_pathkeys, current_pathkeys))
+			if (use_hashed_distinct)
+			{
+				/* Hashed aggregate plan --- no sort needed */
+				result_plan = (Plan *) make_agg(root,
+												result_plan->targetlist,
+												NIL,
+												AGG_HASHED,
+												NULL,
+											  list_length(parse->distinctClause),
+									 extract_grouping_cols(parse->distinctClause,
+														result_plan->targetlist),
+									 extract_grouping_ops(parse->distinctClause),
+												numDistinctRows,
+												result_plan);
+				/* Hashed aggregation produces randomly-ordered results */
+				current_pathkeys = NIL;
+			}
+			else
 			{
-				if (list_length(root->distinct_pathkeys) >=
+				/*
+				 * Use a Unique node to implement DISTINCT.  Add an explicit sort
+				 * if we couldn't make the path come out the way the Unique node
+				 * needs it.  If we do have to sort, always sort by the more
+				 * rigorous of DISTINCT and ORDER BY, to avoid a second sort
+				 * below.  However, for regular DISTINCT, don't sort now if we
+				 * don't have to --- sorting afterwards will likely be cheaper,
+				 * and also has the possibility of optimizing via LIMIT.  But for
+				 * DISTINCT ON, we *must* force the final sort now, else it won't
+				 * have the desired behavior.
+				 */
+				List	   *needed_pathkeys;
+
+				if (parse->hasDistinctOn &&
+					list_length(root->distinct_pathkeys) <
 					list_length(root->sort_pathkeys))
-					current_pathkeys = root->distinct_pathkeys;
+					needed_pathkeys = root->sort_pathkeys;
 				else
+					needed_pathkeys = root->distinct_pathkeys;
+
+				if (!pathkeys_contained_in(needed_pathkeys, current_pathkeys))
 				{
-					current_pathkeys = root->sort_pathkeys;
-					/* Assert checks that parser didn't mess up... */
-					Assert(pathkeys_contained_in(root->distinct_pathkeys,
-												 current_pathkeys));
+					if (list_length(root->distinct_pathkeys) >=
+						list_length(root->sort_pathkeys))
+						current_pathkeys = root->distinct_pathkeys;
+					else
+					{
+						current_pathkeys = root->sort_pathkeys;
+						/* Assert checks that parser didn't mess up... */
+						Assert(pathkeys_contained_in(root->distinct_pathkeys,
+													 current_pathkeys));
+					}
+
+					result_plan = (Plan *) make_sort_from_pathkeys(root,
+																   result_plan,
+																current_pathkeys,
+																   -1.0);
 				}
 
+				result_plan = (Plan *) make_unique(result_plan,
+												   parse->distinctClause);
+				result_plan->plan_rows = dNumDistinctRows;
+				/* The Unique node won't change sort ordering */
+			}
+		}
+
+		/*
+		 * If ORDER BY was given and we were not able to make the plan come out in
+		 * the right order, add an explicit sort step.
+		 */
+		if (parse->sortClause)
+		{
+			if (!pathkeys_contained_in(root->sort_pathkeys, current_pathkeys))
+			{
 				result_plan = (Plan *) make_sort_from_pathkeys(root,
 															   result_plan,
-															current_pathkeys,
-															   -1.0);
+															 root->sort_pathkeys,
+															   limit_tuples);
+				current_pathkeys = root->sort_pathkeys;
 			}
-
-			result_plan = (Plan *) make_unique(result_plan,
-											   parse->distinctClause);
-			result_plan->plan_rows = dNumDistinctRows;
-			/* The Unique node won't change sort ordering */
 		}
-	}
 
-	/*
-	 * If ORDER BY was given and we were not able to make the plan come out in
-	 * the right order, add an explicit sort step.
-	 */
-	if (parse->sortClause)
-	{
-		if (!pathkeys_contained_in(root->sort_pathkeys, current_pathkeys))
+		/*
+		 * If there is a FOR [KEY] UPDATE/SHARE clause, add the LockRows node.
+		 * (Note: we intentionally test parse->rowMarks not root->rowMarks here.
+		 * If there are only non-locking rowmarks, they should be handled by the
+		 * ModifyTable node instead.)
+		 */
+		if (parse->rowMarks)
 		{
-			result_plan = (Plan *) make_sort_from_pathkeys(root,
-														   result_plan,
-														 root->sort_pathkeys,
-														   limit_tuples);
-			current_pathkeys = root->sort_pathkeys;
-		}
-	}
+			result_plan = (Plan *) make_lockrows(result_plan,
+												 root->rowMarks,
+												 SS_assign_special_param(root));
 
-	/*
-	 * If there is a FOR [KEY] UPDATE/SHARE clause, add the LockRows node.
-	 * (Note: we intentionally test parse->rowMarks not root->rowMarks here.
-	 * If there are only non-locking rowmarks, they should be handled by the
-	 * ModifyTable node instead.)
-	 */
-	if (parse->rowMarks)
-	{
-		result_plan = (Plan *) make_lockrows(result_plan,
-											 root->rowMarks,
-											 SS_assign_special_param(root));
+			/*
+			 * The result can no longer be assumed sorted, since locking might
+			 * cause the sort key columns to be replaced with new values.
+			 */
+			current_pathkeys = NIL;
+		}
 
 		/*
-		 * The result can no longer be assumed sorted, since locking might
-		 * cause the sort key columns to be replaced with new values.
+		 * Finally, if there is a LIMIT/OFFSET clause, add the LIMIT node.
 		 */
-		current_pathkeys = NIL;
-	}
+		if (limit_needed(parse))
+		{
+			result_plan = (Plan *) make_limit(result_plan,
+											  parse->limitOffset,
+											  parse->limitCount,
+											  offset_est,
+											  count_est);
+		}
 
-	/*
-	 * Finally, if there is a LIMIT/OFFSET clause, add the LIMIT node.
-	 */
-	if (limit_needed(parse))
-	{
-		result_plan = (Plan *) make_limit(result_plan,
-										  parse->limitOffset,
-										  parse->limitCount,
-										  offset_est,
-										  count_est);
-	}
+		lfirst(lc) = result_plan;
+	} /* foreach all_plans */
 
 	/*
 	 * Return the actual output ordering in query_pathkeys for possible use by
@@ -1999,7 +2019,16 @@ grouping_planner(PlannerInfo *root, double tuple_fraction)
 	 */
 	root->query_pathkeys = current_pathkeys;
 
-	return result_plan;
+	/* if there is only one plan, then just return that plan */
+	if (list_length(result_plan_list) == 1)
+		return (Plan *) linitial(result_plan_list);
+
+	/*
+	 * Otherwise we'd better add an AlternativePlan node to allow the executor
+	 * to decide which plan to use.
+	 */
+	else
+		return (Plan *) make_alternativeplan(result_plan_list);
 }
 
 /*
diff --git a/src/backend/optimizer/plan/setrefs.c b/src/backend/optimizer/plan/setrefs.c
index 4d3fbca..042f8b1 100644
--- a/src/backend/optimizer/plan/setrefs.c
+++ b/src/backend/optimizer/plan/setrefs.c
@@ -435,6 +435,17 @@ set_plan_refs(PlannerInfo *root, Plan *plan, int rtoffset)
 	 */
 	switch (nodeTag(plan))
 	{
+		case T_AlternativePlan:
+			{
+				AlternativePlan *aplan = (AlternativePlan *) plan;
+				ListCell *lc;
+				foreach(lc, aplan->planList)
+				{
+					Plan *plan = (Plan *) lfirst(lc);
+					set_plan_refs(root, plan, rtoffset);
+				}
+			}
+			break;
 		case T_SeqScan:
 			{
 				SeqScan    *splan = (SeqScan *) plan;
diff --git a/src/backend/optimizer/util/plancat.c b/src/backend/optimizer/util/plancat.c
index b2becfa..fea198e 100644
--- a/src/backend/optimizer/util/plancat.c
+++ b/src/backend/optimizer/util/plancat.c
@@ -25,7 +25,9 @@
 #include "access/transam.h"
 #include "access/xlog.h"
 #include "catalog/catalog.h"
+#include "catalog/pg_constraint.h"
 #include "catalog/heap.h"
+#include "catalog/pg_type.h"
 #include "foreign/fdwapi.h"
 #include "miscadmin.h"
 #include "nodes/makefuncs.h"
@@ -38,6 +40,7 @@
 #include "parser/parsetree.h"
 #include "rewrite/rewriteManip.h"
 #include "storage/bufmgr.h"
+#include "utils/fmgroids.h"
 #include "utils/lsyscache.h"
 #include "utils/rel.h"
 #include "utils/snapmgr.h"
@@ -89,6 +92,12 @@ get_relation_info(PlannerInfo *root, Oid relationObjectId, bool inhparent,
 	Relation	relation;
 	bool		hasindex;
 	List	   *indexinfos = NIL;
+	List	   *fkinfos = NIL;
+	Relation	fkeyRel;
+	Relation	fkeyRelIdx;
+	ScanKeyData fkeyScankey;
+	SysScanDesc fkeyScan;
+	HeapTuple	tuple;
 
 	/*
 	 * We need not lock the relation since it was already locked, either by
@@ -384,6 +393,111 @@ get_relation_info(PlannerInfo *root, Oid relationObjectId, bool inhparent,
 
 	heap_close(relation, NoLock);
 
+	/* load foreign key constraints */
+	ScanKeyInit(&fkeyScankey,
+				Anum_pg_constraint_conrelid,
+				BTEqualStrategyNumber, F_OIDEQ,
+				ObjectIdGetDatum(relationObjectId));
+
+	fkeyRel = heap_open(ConstraintRelationId, AccessShareLock);
+	fkeyRelIdx = index_open(ConstraintRelidIndexId, AccessShareLock);
+	fkeyScan = systable_beginscan_ordered(fkeyRel, fkeyRelIdx, NULL, 1, &fkeyScankey);
+
+	while ((tuple = systable_getnext_ordered(fkeyScan, ForwardScanDirection)) != NULL)
+	{
+		Form_pg_constraint con = (Form_pg_constraint) GETSTRUCT(tuple);
+		ForeignKeyInfo *fkinfo;
+		Datum		adatum;
+		bool		isNull;
+		ArrayType  *arr;
+		int			nelements;
+
+		/* skip if not a foreign key */
+		if (con->contype != CONSTRAINT_FOREIGN)
+			continue;
+
+		/* we're not interested unless the fkey has been validated */
+		if (!con->convalidated)
+			continue;
+
+		fkinfo = (ForeignKeyInfo *) palloc(sizeof(ForeignKeyInfo));
+		fkinfo->conindid = con->conindid;
+		fkinfo->confrelid = con->confrelid;
+		fkinfo->convalidated = con->convalidated;
+		fkinfo->conrelid = con->conrelid;
+		fkinfo->confupdtype = con->confupdtype;
+		fkinfo->confdeltype = con->confdeltype;
+		fkinfo->confmatchtype = con->confmatchtype;
+
+		adatum = heap_getattr(tuple, Anum_pg_constraint_conkey,
+							RelationGetDescr(fkeyRel), &isNull);
+
+		if (isNull)
+			elog(ERROR, "null conkey for constraint %u",
+				HeapTupleGetOid(tuple));
+
+		arr = DatumGetArrayTypeP(adatum);		/* ensure not toasted */
+		nelements = ARR_DIMS(arr)[0];
+		if (ARR_NDIM(arr) != 1 ||
+			nelements < 0 ||
+			ARR_HASNULL(arr) ||
+			ARR_ELEMTYPE(arr) != INT2OID)
+			elog(ERROR, "conkey is not a 1-D smallint array");
+
+		fkinfo->conkey = (int16 *) ARR_DATA_PTR(arr);
+		fkinfo->conncols = nelements;
+
+		adatum = heap_getattr(tuple, Anum_pg_constraint_confkey,
+							RelationGetDescr(fkeyRel), &isNull);
+
+		if (isNull)
+			elog(ERROR, "null confkey for constraint %u",
+				HeapTupleGetOid(tuple));
+
+		arr = DatumGetArrayTypeP(adatum);		/* ensure not toasted */
+		nelements = ARR_DIMS(arr)[0];
+
+		if (ARR_NDIM(arr) != 1 ||
+			nelements < 0 ||
+			ARR_HASNULL(arr) ||
+			ARR_ELEMTYPE(arr) != INT2OID)
+			elog(ERROR, "confkey is not a 1-D smallint array");
+
+		/* sanity check */
+		if (nelements != fkinfo->conncols)
+			elog(ERROR, "number of confkey elements does not equal conkey elements");
+
+		fkinfo->confkey = (int16 *) ARR_DATA_PTR(arr);
+		adatum = heap_getattr(tuple, Anum_pg_constraint_conpfeqop,
+							RelationGetDescr(fkeyRel), &isNull);
+
+		if (isNull)
+			elog(ERROR, "null conpfeqop for constraint %u",
+				HeapTupleGetOid(tuple));
+
+		arr = DatumGetArrayTypeP(adatum);		/* ensure not toasted */
+		nelements = ARR_DIMS(arr)[0];
+
+		if (ARR_NDIM(arr) != 1 ||
+			nelements < 0 ||
+			ARR_HASNULL(arr) ||
+			ARR_ELEMTYPE(arr) != OIDOID)
+			elog(ERROR, "conpfeqop is not a 1-D smallint array");
+
+		/* sanity check */
+		if (nelements != fkinfo->conncols)
+			elog(ERROR, "number of conpfeqop elements does not equal conkey elements");
+
+		fkinfo->conpfeqop = (Oid *) ARR_DATA_PTR(arr);
+
+		fkinfos = lappend(fkinfos, fkinfo);
+	}
+
+	rel->fklist = fkinfos;
+	systable_endscan_ordered(fkeyScan);
+	index_close(fkeyRelIdx, AccessShareLock);
+	heap_close(fkeyRel, AccessShareLock);
+
 	/*
 	 * Allow a plugin to editorialize on the info we obtained from the
 	 * catalogs.  Actions might include altering the assumed relation size,
diff --git a/src/backend/optimizer/util/relnode.c b/src/backend/optimizer/util/relnode.c
index 4c76f54..349f330 100644
--- a/src/backend/optimizer/util/relnode.c
+++ b/src/backend/optimizer/util/relnode.c
@@ -115,6 +115,7 @@ build_simple_rel(PlannerInfo *root, int relid, RelOptKind reloptkind)
 	rel->lateral_relids = NULL;
 	rel->lateral_referencers = NULL;
 	rel->indexlist = NIL;
+	rel->fklist = NIL;
 	rel->pages = 0;
 	rel->tuples = 0;
 	rel->allvisfrac = 0;
@@ -127,6 +128,7 @@ build_simple_rel(PlannerInfo *root, int relid, RelOptKind reloptkind)
 	rel->baserestrictcost.startup = 0;
 	rel->baserestrictcost.per_tuple = 0;
 	rel->joininfo = NIL;
+	rel->skipFlags = PLAN_SUITABILITY_ALL_PURPOSE;
 	rel->has_eclass_joins = false;
 
 	/* Check type of rtable entry */
@@ -377,6 +379,7 @@ build_join_rel(PlannerInfo *root,
 	joinrel->lateral_relids = NULL;
 	joinrel->lateral_referencers = NULL;
 	joinrel->indexlist = NIL;
+	joinrel->fklist = NIL;
 	joinrel->pages = 0;
 	joinrel->tuples = 0;
 	joinrel->allvisfrac = 0;
@@ -389,6 +392,7 @@ build_join_rel(PlannerInfo *root,
 	joinrel->baserestrictcost.startup = 0;
 	joinrel->baserestrictcost.per_tuple = 0;
 	joinrel->joininfo = NIL;
+	joinrel->skipFlags = PLAN_SUITABILITY_ALL_PURPOSE;
 	joinrel->has_eclass_joins = false;
 
 	/*
diff --git a/src/backend/utils/cache/lsyscache.c b/src/backend/utils/cache/lsyscache.c
index 73138e0..db0f90a 100644
--- a/src/backend/utils/cache/lsyscache.c
+++ b/src/backend/utils/cache/lsyscache.c
@@ -916,6 +916,33 @@ get_atttypetypmodcoll(Oid relid, AttrNumber attnum,
 	ReleaseSysCache(tp);
 }
 
+/*
+ * get_attnotnull
+ *
+ *		Given the relation id and the attribute number,
+ *		return the "attnotnull" field from the attribute relation.
+ */
+bool
+get_attnotnull(Oid relid, AttrNumber attnum)
+{
+	HeapTuple	tp;
+
+	tp = SearchSysCache2(ATTNUM,
+						 ObjectIdGetDatum(relid),
+						 Int16GetDatum(attnum));
+	if (HeapTupleIsValid(tp))
+	{
+		Form_pg_attribute att_tup = (Form_pg_attribute) GETSTRUCT(tp);
+		bool		result;
+
+		result = att_tup->attnotnull;
+		ReleaseSysCache(tp);
+		return result;
+	}
+	else
+		return false;
+}
+
 /*				---------- COLLATION CACHE ----------					 */
 
 /*
diff --git a/src/include/commands/trigger.h b/src/include/commands/trigger.h
index d0b0356..34a75e4 100644
--- a/src/include/commands/trigger.h
+++ b/src/include/commands/trigger.h
@@ -181,6 +181,7 @@ extern void ExecBSTruncateTriggers(EState *estate,
 extern void ExecASTruncateTriggers(EState *estate,
 					   ResultRelInfo *relinfo);
 
+extern bool AfterTriggerQueueIsEmpty(void);
 extern void AfterTriggerBeginXact(void);
 extern void AfterTriggerBeginQuery(void);
 extern void AfterTriggerEndQuery(EState *estate);
diff --git a/src/include/nodes/nodes.h b/src/include/nodes/nodes.h
index bc71fea..0e45f8e 100644
--- a/src/include/nodes/nodes.h
+++ b/src/include/nodes/nodes.h
@@ -77,6 +77,7 @@ typedef enum NodeTag
 	T_SetOp,
 	T_LockRows,
 	T_Limit,
+	T_AlternativePlan,
 	/* these aren't subclasses of Plan: */
 	T_NestLoopParam,
 	T_PlanRowMark,
@@ -123,6 +124,7 @@ typedef enum NodeTag
 	T_SetOpState,
 	T_LockRowsState,
 	T_LimitState,
+	T_AlternativePlanState,
 
 	/*
 	 * TAGS FOR PRIMITIVE NODES (primnodes.h)
diff --git a/src/include/nodes/parsenodes.h b/src/include/nodes/parsenodes.h
index 5eaa435..f1438db 100644
--- a/src/include/nodes/parsenodes.h
+++ b/src/include/nodes/parsenodes.h
@@ -734,6 +734,10 @@ typedef enum RTEKind
 	RTE_CTE						/* common table expr (WITH list element) */
 } RTEKind;
 
+/* Bit flags to mark suitability of plans */
+#define PLAN_SUITABILITY_ALL_PURPOSE		0
+#define PLAN_SUITABILITY_FK_TRIGGER_EMPTY	1
+
 typedef struct RangeTblEntry
 {
 	NodeTag		type;
diff --git a/src/include/nodes/plannodes.h b/src/include/nodes/plannodes.h
index 48203a0..9169d36 100644
--- a/src/include/nodes/plannodes.h
+++ b/src/include/nodes/plannodes.h
@@ -70,8 +70,11 @@ typedef struct PlannedStmt
 
 	int			nParamExec;		/* number of PARAM_EXEC Params used */
 
+	int			suitableFor; /* under which conditions can this plan be used */
+
 	bool		hasRowSecurity;	/* row security applied? */
 
+
 } PlannedStmt;
 
 /* macro for fetching the Plan associated with a SubPlan node */
@@ -767,6 +770,20 @@ typedef struct LockRows
 	int			epqParam;		/* ID of Param for EvalPlanQual re-eval */
 } LockRows;
 
+
+/* ----------------
+ *		alternative plan node
+ *
+ * Stores a list of alternative plans and one
+ * all purpose plan.
+ * ----------------
+ */
+typedef struct AlternativePlan
+{
+	Plan		plan;
+	List	   *planList;
+} AlternativePlan;
+
 /* ----------------
  *		limit node
  *
diff --git a/src/include/nodes/relation.h b/src/include/nodes/relation.h
index 7116496..6cfaecd 100644
--- a/src/include/nodes/relation.h
+++ b/src/include/nodes/relation.h
@@ -95,6 +95,8 @@ typedef struct PlannerGlobal
 
 	int			nParamExec;		/* number of PARAM_EXEC Params used */
 
+	int			suitableFor; /* under which conditions can this plan be used */
+
 	Index		lastPHId;		/* highest PlaceHolderVar ID assigned */
 
 	Index		lastRowMarkId;	/* highest PlanRowMark ID assigned */
@@ -103,6 +105,7 @@ typedef struct PlannerGlobal
 
 	bool		hasRowSecurity;	/* row security applied? */
 
+
 } PlannerGlobal;
 
 /* macro for fetching the Plan associated with a SubPlan node */
@@ -359,6 +362,8 @@ typedef struct PlannerInfo
  *		lateral_referencers - relids of rels that reference this one laterally
  *		indexlist - list of IndexOptInfo nodes for relation's indexes
  *					(always NIL if it's not a table)
+ *		fklist - list of ForeignKeyInfo's for relation's foreign key
+ *					constraints. (always NIL if it's not a table)
  *		pages - number of disk pages in relation (zero if not a table)
  *		tuples - number of tuples in relation (not considering restrictions)
  *		allvisfrac - fraction of disk pages that are marked all-visible
@@ -452,6 +457,7 @@ typedef struct RelOptInfo
 	Relids		lateral_relids; /* minimum parameterization of rel */
 	Relids		lateral_referencers;	/* rels that reference me laterally */
 	List	   *indexlist;		/* list of IndexOptInfo */
+	List	   *fklist;			/* list of ForeignKeyInfo */
 	BlockNumber pages;			/* size estimates derived from pg_class */
 	double		tuples;
 	double		allvisfrac;
@@ -469,6 +475,8 @@ typedef struct RelOptInfo
 	QualCost	baserestrictcost;		/* cost of evaluating the above */
 	List	   *joininfo;		/* RestrictInfo structures for join clauses
 								 * involving this rel */
+	int			skipFlags;		/* it may be possible to not bother joining
+								 * this relation at all */
 	bool		has_eclass_joins;		/* T means joininfo is incomplete */
 } RelOptInfo;
 
@@ -542,6 +550,51 @@ typedef struct IndexOptInfo
 	bool		amhasgetbitmap; /* does AM have amgetbitmap interface? */
 } IndexOptInfo;
 
+/*
+ * ForeignKeyInfo
+ *		Used to store pg_constraint records for foreign key constraints for use
+ *		by the planner.
+ *
+ *		conindid - The index which supports the foreign key
+ *
+ *		confrelid - The relation that is referenced by this foreign key
+ *
+ *		convalidated - True if the foreign key has been validated.
+ *
+ *		conrelid - The Oid of the relation that the foreign key belongs to
+ *
+ *		confupdtype - ON UPDATE action for when the referenced table is updated
+ *
+ *		confdeltype - ON DELETE action, controls what to do when a record is
+ *					deleted from the referenced table.
+ *
+ *		confmatchtype - foreign key match type, e.g MATCH FULL, MATCH PARTIAL
+ *
+ *		conncols - Number of columns defined in the foreign key
+ *
+ *		conkey - An array of conncols elements to store the varattno of the
+ *					columns on the referencing side of the foreign key
+ *
+ *		confkey - An array of conncols elements to store the varattno of the
+ *					columns on the referenced side of the foreign key
+ *
+ *		conpfeqop - An array of conncols elements to store the operators for
+ *					PK = FK comparisons
+ */
+typedef struct ForeignKeyInfo
+{
+	Oid			conindid;		/* index supporting this constraint */
+	Oid			confrelid;		/* relation referenced by foreign key */
+	bool		convalidated;	/* constraint has been validated? */
+	Oid			conrelid;		/* relation this constraint constrains */
+	char		confupdtype;	/* foreign key's ON UPDATE action */
+	char		confdeltype;	/* foreign key's ON DELETE action */
+	char		confmatchtype;	/* foreign key's match type */
+	int			conncols;		/* number of columns references */
+	int16	   *conkey;			/* Columns of conrelid that the constraint applies to */
+	int16	   *confkey;		/* columns of confrelid that foreign key references */
+	Oid		   *conpfeqop;		/* Operator list for comparing PK to FK */
+} ForeignKeyInfo;
 
 /*
  * EquivalenceClasses
diff --git a/src/include/optimizer/paths.h b/src/include/optimizer/paths.h
index afa5f9b..ff9f4cd 100644
--- a/src/include/optimizer/paths.h
+++ b/src/include/optimizer/paths.h
@@ -37,7 +37,8 @@ typedef RelOptInfo *(*join_search_hook_type) (PlannerInfo *root,
 extern PGDLLIMPORT join_search_hook_type join_search_hook;
 
 
-extern RelOptInfo *make_one_rel(PlannerInfo *root, List *joinlist);
+extern RelOptInfo *make_one_rel(PlannerInfo *root, List *joinlist,
+								int skipflags);
 extern RelOptInfo *standard_join_search(PlannerInfo *root, int levels_needed,
 					 List *initial_rels);
 
@@ -119,6 +120,8 @@ extern List *generate_join_implied_equalities(PlannerInfo *root,
 								 Relids join_relids,
 								 Relids outer_relids,
 								 RelOptInfo *inner_rel);
+extern Oid select_equality_operator(EquivalenceClass *ec, Oid lefttype,
+								 Oid righttype);
 extern bool exprs_known_equal(PlannerInfo *root, Node *item1, Node *item2);
 extern void add_child_rel_equivalences(PlannerInfo *root,
 						   AppendRelInfo *appinfo,
diff --git a/src/include/optimizer/planmain.h b/src/include/optimizer/planmain.h
index 3fdc2cb..0d2ebb9 100644
--- a/src/include/optimizer/planmain.h
+++ b/src/include/optimizer/planmain.h
@@ -27,8 +27,9 @@ typedef void (*query_pathkeys_callback) (PlannerInfo *root, void *extra);
 /*
  * prototypes for plan/planmain.c
  */
-extern RelOptInfo *query_planner(PlannerInfo *root, List *tlist,
-			  query_pathkeys_callback qp_callback, void *qp_extra);
+extern List *query_planner(PlannerInfo *root, List *tlist,
+			  query_pathkeys_callback qp_callback, void *qp_extra,
+			  bool alternativePlans);
 
 /*
  * prototypes for plan/planagg.c
@@ -73,6 +74,7 @@ extern Group *make_group(PlannerInfo *root, List *tlist, List *qual,
 extern Plan *materialize_finished_plan(Plan *subplan);
 extern Unique *make_unique(Plan *lefttree, List *distinctList);
 extern LockRows *make_lockrows(Plan *lefttree, List *rowMarks, int epqParam);
+extern AlternativePlan *make_alternativeplan(List *planlist);
 extern Limit *make_limit(Plan *lefttree, Node *limitOffset, Node *limitCount,
 		   int64 offset_est, int64 count_est);
 extern SetOp *make_setop(SetOpCmd cmd, SetOpStrategy strategy, Plan *lefttree,
diff --git a/src/include/utils/lsyscache.h b/src/include/utils/lsyscache.h
index 1a556f8..1cb9970 100644
--- a/src/include/utils/lsyscache.h
+++ b/src/include/utils/lsyscache.h
@@ -68,6 +68,7 @@ extern Oid	get_atttype(Oid relid, AttrNumber attnum);
 extern int32 get_atttypmod(Oid relid, AttrNumber attnum);
 extern void get_atttypetypmodcoll(Oid relid, AttrNumber attnum,
 					  Oid *typid, int32 *typmod, Oid *collid);
+extern bool get_attnotnull(Oid relid, AttrNumber attnum);
 extern char *get_collation_name(Oid colloid);
 extern char *get_constraint_name(Oid conoid);
 extern Oid	get_opclass_family(Oid opclass);
diff --git a/src/test/regress/expected/join.out b/src/test/regress/expected/join.out
index 2501184..e485554 100644
--- a/src/test/regress/expected/join.out
+++ b/src/test/regress/expected/join.out
@@ -3276,6 +3276,171 @@ select i8.* from int8_tbl i8 left join (select f1 from int4_tbl group by f1) i4
 (1 row)
 
 rollback;
+begin work;
+create temp table c (
+  id int primary key
+);
+create temp table b (
+  id int primary key,
+  c_id int not null,
+  val int not null,
+  constraint b_c_id_fkey foreign key (c_id) references c deferrable
+);
+create temp table a (
+  id int primary key,
+  b_id int not null,
+  constraint a_b_id_fkey foreign key (b_id) references b deferrable
+);
+insert into c (id) values(1);
+insert into b (id,c_id,val) values(2,1,10);
+insert into a (id,b_id) values(3,2);
+-- this should remove inner join to b
+explain (costs off)
+select a.* from a inner join b on a.b_id = b.id;
+  QUERY PLAN   
+---------------
+ Seq Scan on a
+(1 row)
+
+-- this should remove inner join to b and c
+explain (costs off)
+select a.* from a inner join b on a.b_id = b.id inner join c on b.c_id = c.id;
+  QUERY PLAN   
+---------------
+ Seq Scan on a
+(1 row)
+
+-- Ensure all of the target entries have their proper aliases.
+select a.* from a inner join b on a.b_id = b.id inner join c on b.c_id = c.id;
+ id | b_id 
+----+------
+  3 |    2
+(1 row)
+
+-- change order of tables in query, this should generate the same plan as above.
+explain (costs off)
+select a.* from c inner join b on c.id = b.c_id inner join a on a.b_id = b.id;
+  QUERY PLAN   
+---------------
+ Seq Scan on a
+(1 row)
+
+-- inner join can't be removed due to b columns in the target list
+explain (costs off)
+select * from a inner join b on a.b_id = b.id;
+          QUERY PLAN          
+------------------------------
+ Hash Join
+   Hash Cond: (a.b_id = b.id)
+   ->  Seq Scan on a
+   ->  Hash
+         ->  Seq Scan on b
+(5 rows)
+
+-- this should not remove inner join to b due to quals restricting results from b
+explain (costs off)
+select a.* from a inner join b on a.b_id = b.id where b.val = 10;
+            QUERY PLAN            
+----------------------------------
+ Hash Join
+   Hash Cond: (a.b_id = b.id)
+   ->  Seq Scan on a
+   ->  Hash
+         ->  Seq Scan on b
+               Filter: (val = 10)
+(6 rows)
+
+-- this should not remove join to b
+explain (costs off)
+select a.* from a inner join b on a.b_id = b.id where b.val = b.id;
+            QUERY PLAN            
+----------------------------------
+ Hash Join
+   Hash Cond: (a.b_id = b.id)
+   ->  Seq Scan on a
+   ->  Hash
+         ->  Seq Scan on b
+               Filter: (id = val)
+(6 rows)
+
+-- this should not remove the join, no foreign key exists between a.id and b.id
+explain (costs off)
+select a.* from a inner join b on a.id = b.id;
+         QUERY PLAN         
+----------------------------
+ Hash Join
+   Hash Cond: (a.id = b.id)
+   ->  Seq Scan on a
+   ->  Hash
+         ->  Seq Scan on b
+(5 rows)
+
+-- ensure a left joined rel can't remove an inner joined rel
+explain (costs off)
+select a.* from b left join a on b.id = a.b_id;
+          QUERY PLAN          
+------------------------------
+ Hash Right Join
+   Hash Cond: (a.b_id = b.id)
+   ->  Seq Scan on a
+   ->  Hash
+         ->  Seq Scan on b
+(5 rows)
+
+-- Ensure we remove b, but don't try and remove c. c has no join condition.
+explain (costs off)
+select a.* from a inner join b on a.b_id = b.id cross join c;
+        QUERY PLAN         
+---------------------------
+ Nested Loop
+   ->  Seq Scan on c
+   ->  Materialize
+         ->  Seq Scan on a
+(4 rows)
+
+set constraints b_c_id_fkey deferred;
+-- join should be removed.
+explain (costs off)
+select b.* from b inner join c on b.c_id = c.id;
+  QUERY PLAN   
+---------------
+ Seq Scan on b
+(1 row)
+
+prepare ab as select b.* from b inner join c on b.c_id = c.id;
+explain (costs off)
+execute ab;
+  QUERY PLAN   
+---------------
+ Seq Scan on b
+(1 row)
+
+-- perform an update which will cause some pending fk triggers to be added
+update c set id = 2 where id=1;
+-- ensure inner join is no longer removed.
+explain (costs off)
+select b.* from b inner join c on b.c_id = c.id;
+          QUERY PLAN          
+------------------------------
+ Hash Join
+   Hash Cond: (b.c_id = c.id)
+   ->  Seq Scan on b
+   ->  Hash
+         ->  Seq Scan on c
+(5 rows)
+
+explain (costs off)
+execute ab;
+          QUERY PLAN          
+------------------------------
+ Hash Join
+   Hash Cond: (b.c_id = c.id)
+   ->  Seq Scan on b
+   ->  Hash
+         ->  Seq Scan on c
+(5 rows)
+
+rollback;
 create temp table parent (k int primary key, pd int);
 create temp table child (k int unique, cd int);
 insert into parent values (1, 10), (2, 20), (3, 30);
diff --git a/src/test/regress/sql/join.sql b/src/test/regress/sql/join.sql
index 718e1d9..c3ee72e 100644
--- a/src/test/regress/sql/join.sql
+++ b/src/test/regress/sql/join.sql
@@ -977,6 +977,89 @@ select i8.* from int8_tbl i8 left join (select f1 from int4_tbl group by f1) i4
 
 rollback;
 
+begin work;
+
+create temp table c (
+  id int primary key
+);
+create temp table b (
+  id int primary key,
+  c_id int not null,
+  val int not null,
+  constraint b_c_id_fkey foreign key (c_id) references c deferrable
+);
+create temp table a (
+  id int primary key,
+  b_id int not null,
+  constraint a_b_id_fkey foreign key (b_id) references b deferrable
+);
+
+insert into c (id) values(1);
+insert into b (id,c_id,val) values(2,1,10);
+insert into a (id,b_id) values(3,2);
+
+-- this should remove inner join to b
+explain (costs off)
+select a.* from a inner join b on a.b_id = b.id;
+
+-- this should remove inner join to b and c
+explain (costs off)
+select a.* from a inner join b on a.b_id = b.id inner join c on b.c_id = c.id;
+
+-- Ensure all of the target entries have their proper aliases.
+select a.* from a inner join b on a.b_id = b.id inner join c on b.c_id = c.id;
+
+-- change order of tables in query, this should generate the same plan as above.
+explain (costs off)
+select a.* from c inner join b on c.id = b.c_id inner join a on a.b_id = b.id;
+
+-- inner join can't be removed due to b columns in the target list
+explain (costs off)
+select * from a inner join b on a.b_id = b.id;
+
+-- this should not remove inner join to b due to quals restricting results from b
+explain (costs off)
+select a.* from a inner join b on a.b_id = b.id where b.val = 10;
+
+-- this should not remove join to b
+explain (costs off)
+select a.* from a inner join b on a.b_id = b.id where b.val = b.id;
+
+-- this should not remove the join, no foreign key exists between a.id and b.id
+explain (costs off)
+select a.* from a inner join b on a.id = b.id;
+
+-- ensure a left joined rel can't remove an inner joined rel
+explain (costs off)
+select a.* from b left join a on b.id = a.b_id;
+
+-- Ensure we remove b, but don't try and remove c. c has no join condition.
+explain (costs off)
+select a.* from a inner join b on a.b_id = b.id cross join c;
+
+set constraints b_c_id_fkey deferred;
+
+-- join should be removed.
+explain (costs off)
+select b.* from b inner join c on b.c_id = c.id;
+
+prepare ab as select b.* from b inner join c on b.c_id = c.id;
+
+explain (costs off)
+execute ab;
+
+-- perform an update which will cause some pending fk triggers to be added
+update c set id = 2 where id=1;
+
+-- ensure inner join is no longer removed.
+explain (costs off)
+select b.* from b inner join c on b.c_id = c.id;
+
+explain (costs off)
+execute ab;
+
+rollback;
+
 create temp table parent (k int primary key, pd int);
 create temp table child (k int unique, cd int);
 insert into parent values (1, 10), (2, 20), (3, 30);

diff --git a/src/backend/commands/trigger.c b/src/backend/commands/trigger.c
index 4899a27..43bc425 100644
--- a/src/backend/commands/trigger.c
+++ b/src/backend/commands/trigger.c
@@ -3889,6 +3889,17 @@ afterTriggerInvokeEvents(AfterTriggerEventList *events,
 	return all_fired;
 }
 
+/* ----------
+ * AfterTriggerQueueIsEmpty()
+ *
+ *	True if there are no pending triggers in the queue.
+ * ----------
+ */
+bool
+AfterTriggerQueueIsEmpty(void)
+{
+	return (afterTriggers.query_depth == -1 && afterTriggers.events.head == NULL);
+}
 
 /* ----------
  * AfterTriggerBeginXact()
diff --git a/src/backend/executor/Makefile b/src/backend/executor/Makefile
index af707b0..bfbd5b3 100644
--- a/src/backend/executor/Makefile
+++ b/src/backend/executor/Makefile
@@ -14,8 +14,8 @@ include $(top_builddir)/src/Makefile.global
 
 OBJS = execAmi.o execCurrent.o execGrouping.o execJunk.o execMain.o \
        execProcnode.o execQual.o execScan.o execTuples.o \
-       execUtils.o functions.o instrument.o nodeAppend.o nodeAgg.o \
-       nodeBitmapAnd.o nodeBitmapOr.o \
+       execUtils.o functions.o instrument.o nodeAlternativePlan.o nodeAppend.o \
+       nodeAgg.o nodeBitmapAnd.o nodeBitmapOr.o \
        nodeBitmapHeapscan.o nodeBitmapIndexscan.o nodeCustom.o nodeHash.o \
        nodeHashjoin.o nodeIndexscan.o nodeIndexonlyscan.o \
        nodeLimit.o nodeLockRows.o \
diff --git a/src/backend/executor/execProcnode.c b/src/backend/executor/execProcnode.c
index 9892499..523e187 100644
--- a/src/backend/executor/execProcnode.c
+++ b/src/backend/executor/execProcnode.c
@@ -79,6 +79,7 @@
 
 #include "executor/executor.h"
 #include "executor/nodeAgg.h"
+#include "executor/nodeAlternativePlan.h"
 #include "executor/nodeAppend.h"
 #include "executor/nodeBitmapAnd.h"
 #include "executor/nodeBitmapHeapscan.h"
@@ -147,6 +148,11 @@ ExecInitNode(Plan *node, EState *estate, int eflags)
 			/*
 			 * control nodes
 			 */
+		case T_AlternativePlan:
+			result = (PlanState *) ExecInitAlternativePlan((AlternativePlan *)node,
+												  estate, eflags);
+			break;
+
 		case T_Result:
 			result = (PlanState *) ExecInitResult((Result *) node,
 												  estate, eflags);
diff --git a/src/backend/executor/nodeAlternativePlan.c b/src/backend/executor/nodeAlternativePlan.c
new file mode 100644
index 0000000..cafe33a
--- /dev/null
+++ b/src/backend/executor/nodeAlternativePlan.c
@@ -0,0 +1,51 @@
+/*-------------------------------------------------------------------------
+ *
+ * nodeAlternativePlan.c
+ *	  Node to support storage of alternative plans.
+ *
+ *	  Note that this node is rather special as it only exists while the plan
+ *	  is being initialised.
+ *
+ *	  When the initialization method is called for this node, a decision is
+ *	  made to decide which plan should be initialized, the code here then calls
+ *	  the initialize method on the selected plan and returns the state value
+ *	  from the root node of that plan.
+ *
+ * Portions Copyright (c) 1996-2015, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ *
+ * IDENTIFICATION
+ *	  src/backend/executor/nodeAlternativePlan.c
+ *
+ *-------------------------------------------------------------------------
+ */
+
+#include "postgres.h"
+
+#include "commands/trigger.h"
+
+#include "executor/executor.h"
+#include "executor/nodeAlternativePlan.h"
+
+PlanState *
+ExecInitAlternativePlan(AlternativePlan *node, EState *estate, int eflags)
+{
+	/*
+	 * If we have items in the fk trigger queue, then we'd better use the all
+	 * all purpose plan. Since an AlternativePlan node has no state, we simply
+	 * just initialize the root node of the selected plan. This means that the
+	 * AlternativePlan node is *never* seen in EXPLAIN or EXPLAIN ANALYZE.
+	 */
+	if (!AfterTriggerQueueIsEmpty())
+		return (PlanState *) ExecInitNode((Plan *) list_nth(node->planList, 1),
+											estate, eflags);
+
+	/*
+	 * Otherwise we initialize the root node of the optimized plan and return
+	 * that.
+	 */
+	else
+		return (PlanState *) ExecInitNode((Plan *) linitial(node->planList),
+											estate, eflags);
+}
diff --git a/src/backend/nodes/copyfuncs.c b/src/backend/nodes/copyfuncs.c
index f1a24f5..3cd1a4e 100644
--- a/src/backend/nodes/copyfuncs.c
+++ b/src/backend/nodes/copyfuncs.c
@@ -93,6 +93,7 @@ _copyPlannedStmt(const PlannedStmt *from)
 	COPY_NODE_FIELD(relationOids);
 	COPY_NODE_FIELD(invalItems);
 	COPY_SCALAR_FIELD(nParamExec);
+	COPY_SCALAR_FIELD(suitableFor);
 
 	return newnode;
 }
@@ -963,6 +964,16 @@ _copyLimit(const Limit *from)
 	return newnode;
 }
 
+static AlternativePlan *
+_copyAlternativePlan(const AlternativePlan *from)
+{
+	AlternativePlan *newnode = makeNode(AlternativePlan);
+
+	COPY_NODE_FIELD(planList);
+
+	return newnode;
+}
+
 /*
  * _copyNestLoopParam
  */
@@ -4117,6 +4128,9 @@ copyObject(const void *from)
 		case T_Limit:
 			retval = _copyLimit(from);
 			break;
+		case T_AlternativePlan:
+			retval = _copyAlternativePlan(from);
+			break;
 		case T_NestLoopParam:
 			retval = _copyNestLoopParam(from);
 			break;
diff --git a/src/backend/nodes/outfuncs.c b/src/backend/nodes/outfuncs.c
index dd1278b..9824b3d 100644
--- a/src/backend/nodes/outfuncs.c
+++ b/src/backend/nodes/outfuncs.c
@@ -255,6 +255,7 @@ _outPlannedStmt(StringInfo str, const PlannedStmt *node)
 	WRITE_NODE_FIELD(relationOids);
 	WRITE_NODE_FIELD(invalItems);
 	WRITE_INT_FIELD(nParamExec);
+	WRITE_INT_FIELD(suitableFor);
 }
 
 /*
@@ -1716,6 +1717,7 @@ _outPlannerGlobal(StringInfo str, const PlannerGlobal *node)
 	WRITE_UINT_FIELD(lastPHId);
 	WRITE_UINT_FIELD(lastRowMarkId);
 	WRITE_BOOL_FIELD(transientPlan);
+	WRITE_INT_FIELD(suitableFor);
 }
 
 static void
@@ -1801,6 +1803,7 @@ _outRelOptInfo(StringInfo str, const RelOptInfo *node)
 	/* we don't try to print fdwroutine or fdw_private */
 	WRITE_NODE_FIELD(baserestrictinfo);
 	WRITE_NODE_FIELD(joininfo);
+	WRITE_INT_FIELD(removal_flags);
 	WRITE_BOOL_FIELD(has_eclass_joins);
 }
 
diff --git a/src/backend/optimizer/path/allpaths.c b/src/backend/optimizer/path/allpaths.c
index 58d78e6..69990a2 100644
--- a/src/backend/optimizer/path/allpaths.c
+++ b/src/backend/optimizer/path/allpaths.c
@@ -97,7 +97,8 @@ static void set_cte_pathlist(PlannerInfo *root, RelOptInfo *rel,
 				 RangeTblEntry *rte);
 static void set_worktable_pathlist(PlannerInfo *root, RelOptInfo *rel,
 					   RangeTblEntry *rte);
-static RelOptInfo *make_rel_from_joinlist(PlannerInfo *root, List *joinlist);
+static RelOptInfo *make_rel_from_joinlist(PlannerInfo *root, List *joinlist,
+					   int removal_flags);
 static bool subquery_is_pushdown_safe(Query *subquery, Query *topquery,
 						  pushdown_safety_info *safetyInfo);
 static bool recurse_pushdown_safe(Node *setOp, Query *topquery,
@@ -122,7 +123,7 @@ static void remove_unused_subquery_outputs(Query *subquery, RelOptInfo *rel);
  *	  single rel that represents the join of all base rels in the query.
  */
 RelOptInfo *
-make_one_rel(PlannerInfo *root, List *joinlist)
+make_one_rel(PlannerInfo *root, List *joinlist, int removal_flags)
 {
 	RelOptInfo *rel;
 	Index		rti;
@@ -142,7 +143,8 @@ make_one_rel(PlannerInfo *root, List *joinlist)
 		Assert(brel->relid == rti);		/* sanity check on array */
 
 		/* ignore RTEs that are "other rels" */
-		if (brel->reloptkind != RELOPT_BASEREL)
+		if (brel->reloptkind != RELOPT_BASEREL ||
+			brel->removal_flags & removal_flags)
 			continue;
 
 		root->all_baserels = bms_add_member(root->all_baserels, brel->relid);
@@ -157,12 +159,13 @@ make_one_rel(PlannerInfo *root, List *joinlist)
 	/*
 	 * Generate access paths for the entire join tree.
 	 */
-	rel = make_rel_from_joinlist(root, joinlist);
+	rel = make_rel_from_joinlist(root, joinlist, removal_flags);
+
 
 	/*
 	 * The result should join all and only the query's base rels.
 	 */
-	Assert(bms_equal(rel->relids, root->all_baserels));
+	Assert(bms_is_subset(root->all_baserels, rel->relids));
 
 	return rel;
 }
@@ -1496,7 +1499,7 @@ set_worktable_pathlist(PlannerInfo *root, RelOptInfo *rel, RangeTblEntry *rte)
  * data structure.
  */
 static RelOptInfo *
-make_rel_from_joinlist(PlannerInfo *root, List *joinlist)
+make_rel_from_joinlist(PlannerInfo *root, List *joinlist, int removal_flags)
 {
 	int			levels_needed;
 	List	   *initial_rels;
@@ -1528,11 +1531,23 @@ make_rel_from_joinlist(PlannerInfo *root, List *joinlist)
 			int			varno = ((RangeTblRef *) jlnode)->rtindex;
 
 			thisrel = find_base_rel(root, varno);
+
+			/*
+			 * If this relation can be removed for these removal_flags, then
+			 * we'll not bother including this in the list of relations to join
+			 * to
+			 */
+			if ((thisrel->removal_flags & removal_flags))
+			{
+				/* one less level needed too */
+				levels_needed--;
+				continue;
+			}
 		}
 		else if (IsA(jlnode, List))
 		{
 			/* Recurse to handle subproblem */
-			thisrel = make_rel_from_joinlist(root, (List *) jlnode);
+			thisrel = make_rel_from_joinlist(root, (List *) jlnode, removal_flags);
 		}
 		else
 		{
diff --git a/src/backend/optimizer/path/equivclass.c b/src/backend/optimizer/path/equivclass.c
index eb65c97..8ddc9db 100644
--- a/src/backend/optimizer/path/equivclass.c
+++ b/src/backend/optimizer/path/equivclass.c
@@ -49,8 +49,6 @@ static List *generate_join_implied_equalities_broken(PlannerInfo *root,
 										Relids outer_relids,
 										Relids nominal_inner_relids,
 										RelOptInfo *inner_rel);
-static Oid select_equality_operator(EquivalenceClass *ec,
-						 Oid lefttype, Oid righttype);
 static RestrictInfo *create_join_clause(PlannerInfo *root,
 				   EquivalenceClass *ec, Oid opno,
 				   EquivalenceMember *leftem,
@@ -1282,7 +1280,7 @@ generate_join_implied_equalities_broken(PlannerInfo *root,
  *
  * Returns InvalidOid if no operator can be found for this datatype combination
  */
-static Oid
+Oid
 select_equality_operator(EquivalenceClass *ec, Oid lefttype, Oid righttype)
 {
 	ListCell   *lc;
diff --git a/src/backend/optimizer/plan/analyzejoins.c b/src/backend/optimizer/plan/analyzejoins.c
index 11d3933..e6bfe37 100644
--- a/src/backend/optimizer/plan/analyzejoins.c
+++ b/src/backend/optimizer/plan/analyzejoins.c
@@ -32,13 +32,21 @@
 #include "utils/lsyscache.h"
 
 /* local functions */
-static bool join_is_removable(PlannerInfo *root, SpecialJoinInfo *sjinfo);
+static bool innerjoin_is_removable(PlannerInfo *root, List *joinlist,
+					  RangeTblRef *removalrtr, Relids ignoredrels);
+static bool leftjoin_is_removable(PlannerInfo *root, SpecialJoinInfo *sjinfo);
+static bool relation_is_needed(PlannerInfo *root, Relids joinrelids,
+					  RelOptInfo *rel, Relids ignoredrels);
+static bool relation_has_foreign_key_for(PlannerInfo *root, RelOptInfo *rel,
+					  RelOptInfo *referencedrel, List *referencing_vars,
+					  List *index_vars, List *operator_list);
+static bool expressions_match_foreign_key(ForeignKeyInfo *fk, List *fkvars,
+					  List *indexvars, List *operators);
 static void remove_rel_from_query(PlannerInfo *root, int relid,
 					  Relids joinrelids);
 static List *remove_rel_from_joinlist(List *joinlist, int relid, int *nremoved);
 static Oid	distinct_col_search(int colno, List *colnos, List *opids);
 
-
 /*
  * remove_useless_joins
  *		Check for relations that don't actually need to be joined at all,
@@ -46,26 +54,104 @@ static Oid	distinct_col_search(int colno, List *colnos, List *opids);
  *
  * We are passed the current joinlist and return the updated list.  Other
  * data structures that have to be updated are accessible via "root".
+ *
+ * There are 2 methods here for removing joins. Joins such as LEFT JOINs
+ * which can be proved to be needless due to lack of use of any of the joining
+ * relation's columns and the existence of a unique index on a subset of the
+ * join clause, can simply be removed from the query plan at plan time. For
+ * certain other join types we make use of foreign keys to attempt to prove the
+ * join is needless, though, for these we're unable to be certain that the join
+ * is not required at plan time, as if the plan is executed when pending
+ * foreign key triggers have not yet been fired, then the foreign key is
+ * effectively violated until these triggers have fired. Removing a join in
+ * such a case could cause a query to produce incorrect results.
+ *
+ * Instead we handle this case by marking the RangeTblEntry for the relation
+ * with a special flag which tells the executor that it's possible that joining
+ * to this relation may not be required. The executor may then check this flag
+ * and choose to skip the join based on if there are foreign key triggers
+ * pending or not.
  */
 List *
 remove_useless_joins(PlannerInfo *root, List *joinlist)
 {
 	ListCell   *lc;
+	Relids		removedrels = NULL;
 
 	/*
-	 * We are only interested in relations that are left-joined to, so we can
-	 * scan the join_info_list to find them easily.
+	 * Start by analyzing INNER JOINed relations in order to determine if any
+	 * of the relations can be ignored.
 	 */
 restart:
+	foreach(lc, joinlist)
+	{
+		RangeTblRef		*rtr = (RangeTblRef *) lfirst(lc);
+		RelOptInfo		*rel;
+
+		if (!IsA(rtr, RangeTblRef))
+			continue;
+
+		rel = root->simple_rel_array[rtr->rtindex];
+
+		/* Don't try to remove this one again if we've already removed it */
+		if ((rel->removal_flags & PLAN_SUITABILITY_FK_TRIGGER_EMPTY) != 0)
+			continue;
+
+		/* skip if the join can't be removed */
+		if (!innerjoin_is_removable(root, joinlist, rtr, removedrels))
+			continue;
+
+		/*
+		 * Since we're not actually removing the join here, we need to maintain
+		 * a list of relations that we've "removed" so when we're checking if
+		 * other relations can be removed we'll know that if the to be removed
+		 * relation is only referenced by a relation that we've already removed
+		 * that it can be safely assumed that the relation is not referenced by
+		 * any useful relation.
+		 */
+		removedrels = bms_add_member(removedrels, rtr->rtindex);
+
+		/*
+		 * Mark that this relation is only required when the foreign key trigger
+		 * queue us non-empty.
+		 */
+		rel->removal_flags |= PLAN_SUITABILITY_FK_TRIGGER_EMPTY;
+
+		/*
+		 * Globally mark this plan to say that there are some relations which
+		 * are only required when the foreign key trigger queue is non-empty.
+		 * The planner will later generate 2 plans, 1 which is suitable only
+		 * when all if these bitmask conditions are met, and another which is
+		 * an all purpose plan, which will be used if *any* of the bitmask's
+		 * conditions are not met.
+		 */
+		root->glob->suitableFor |= PLAN_SUITABILITY_FK_TRIGGER_EMPTY;
+
+		/*
+		 * Restart the scan.  This is necessary to ensure we find all removable
+		 * joins independently of their ordering. (note that since we've added
+		 * this relation to the removedrels, we may now realize that other
+		 * relations can also be removed as they're only referenced by the one
+		 * that we've just marked as possibly removable).
+		 */
+		goto restart;
+	}
+
+	/* now process special joins. Currently only left joins are supported */
 	foreach(lc, root->join_info_list)
 	{
 		SpecialJoinInfo *sjinfo = (SpecialJoinInfo *) lfirst(lc);
 		int			innerrelid;
 		int			nremoved;
 
-		/* Skip if not removable */
-		if (!join_is_removable(root, sjinfo))
-			continue;
+		if (sjinfo->jointype == JOIN_LEFT)
+		{
+			/* Skip if not removable */
+			if (!leftjoin_is_removable(root, sjinfo))
+				continue;
+		}
+		else
+			continue; /* we don't support this join type */
 
 		/*
 		 * Currently, join_is_removable can only succeed when the sjinfo's
@@ -91,12 +177,11 @@ restart:
 		root->join_info_list = list_delete_ptr(root->join_info_list, sjinfo);
 
 		/*
-		 * Restart the scan.  This is necessary to ensure we find all
-		 * removable joins independently of ordering of the join_info_list
-		 * (note that removal of attr_needed bits may make a join appear
-		 * removable that did not before).  Also, since we just deleted the
-		 * current list cell, we'd have to have some kluge to continue the
-		 * list scan anyway.
+		 * Restart the scan.  This is necessary to ensure we find all removable
+		 * joins independently of their ordering. (note that removal of
+		 * attr_needed bits may make a join, inner or outer, appear removable
+		 * that did not before).   Also, since we just deleted the current list
+		 * cell, we'd have to have some kluge to continue the list scan anyway.
 		 */
 		goto restart;
 	}
@@ -136,8 +221,226 @@ clause_sides_match_join(RestrictInfo *rinfo, Relids outerrelids,
 }
 
 /*
- * join_is_removable
- *	  Check whether we need not perform this special join at all, because
+ * innerjoin_is_removable
+ *		True if the join to removalrtr can be removed.
+ *
+ * In order to prove a relation which is inner joined is not required we must
+ * be sure that the join would emit exactly 1 row on the join condition. This
+ * differs from the logic which is used for proving LEFT JOINs can be removed,
+ * where it's possible to just check that a unique index exists on the relation
+ * being removed which has a set of columns that is a subset of the columns
+ * seen in the join condition. If no matching row is found then left join would
+ * not remove the non-matched row from the result set. This is not the case
+ * with INNER JOINs, so here we must use foreign keys as proof that the 1 row
+ * exists before we can allow any joins to be removed.
+ */
+static bool
+innerjoin_is_removable(PlannerInfo *root, List *joinlist,
+					   RangeTblRef *removalrtr, Relids ignoredrels)
+{
+	ListCell   *lc;
+	RelOptInfo *removalrel;
+
+	removalrel = find_base_rel(root, removalrtr->rtindex);
+
+	/*
+	 * As foreign keys may only reference base rels which have unique indexes,
+	 * we needn't go any further if we're not dealing with a base rel, or if
+	 * the base rel has no unique indexes. We'd also better abort if the
+	 * rtekind is anything but a relation, as things like sub-queries may have
+	 * grouping or distinct clauses that would cause us not to be able to use
+	 * the foreign key to prove the existence of a row matching the join
+	 * condition. We also abort if the rel has no eclass joins as such a rel
+	 * could well be joined using some operator which is not an equality
+	 * operator, or the rel may not even be inner joined at all.
+	 *
+	 * Here we actually only check if the rel has any indexes, ideally we'd be
+	 * checking for unique indexes, but we could only determine that by looping
+	 * over the indexlist, and this is likely too expensive a check to be worth
+	 * it here.
+	 */
+	if (removalrel->reloptkind != RELOPT_BASEREL ||
+		removalrel->rtekind != RTE_RELATION ||
+		removalrel->has_eclass_joins == false ||
+		removalrel->indexlist == NIL)
+		return false;
+
+	/*
+	 * Currently we disallow the removal if we find any baserestrictinfo items
+	 * on the relation being removed. The reason for this is that these would
+	 * filter out rows and make it so the foreign key cannot prove that we'll
+	 * match exactly 1 row on the join condition. However, this check is
+	 * currently probably a bit overly strict as it should be possible to just
+	 * check and ensure that each Var seen in the baserestrictinfo is also
+	 * present in an eclass and if so, just translate and move the whole
+	 * baserestrictinfo over to the relation which has the foreign key to prove
+	 * that this join is not needed. e.g:
+	 * SELECT a.* FROM a INNER JOIN b ON a.b_id = b.id WHERE b.id = 1;
+	 * could become: SELECT a.* FROM a WHERE a.b_id = 1;
+	 */
+	if (removalrel->baserestrictinfo != NIL)
+		return false;
+
+	/*
+	 * Currently only eclass joins are supported, so if there are any non
+	 * eclass join quals then we'll report the join is non-removable.
+	 */
+	if (removalrel->joininfo != NIL)
+		return false;
+
+	/*
+	 * Now we'll search through each relation in the joinlist to see if we can
+	 * find a relation which has a foreign key which references removalrel on
+	 * the join condition. If we find a rel with a foreign key which matches
+	 * the join condition exactly, then we can be sure that exactly 1 row will
+	 * be matched on the join, if we also see that no Vars from the relation
+	 * are needed, then we can report the join as removable.
+	 */
+	foreach (lc, joinlist)
+	{
+		RangeTblRef	*rtr = (RangeTblRef *) lfirst(lc);
+		RelOptInfo	*rel;
+		ListCell	*lc2;
+		List		*referencing_vars;
+		List		*index_vars;
+		List		*operator_list;
+		Relids		 joinrelids;
+
+		/* we can't remove ourself, or anything other than RangeTblRefs */
+		if (rtr == removalrtr || !IsA(rtr, RangeTblRef))
+			continue;
+
+		rel = find_base_rel(root, rtr->rtindex);
+
+		/*
+		 * The only relation type that can help us is a base rel with at least
+		 * one foreign key defined, if there's no eclass joins then this rel
+		 * is not going to help us prove the removalrel is not needed.
+		 */
+		if (rel->reloptkind != RELOPT_BASEREL ||
+			rel->rtekind != RTE_RELATION ||
+			rel->has_eclass_joins == false ||
+			rel->fklist == NIL)
+			continue;
+
+		/*
+		 * Both rels have eclass joins, but do they have eclass joins to each
+		 * other? Skip this rel if it does not.
+		 */
+		if (!have_relevant_eclass_joinclause(root, rel, removalrel))
+			continue;
+
+		joinrelids = bms_union(rel->relids, removalrel->relids);
+
+		/* if any of the Vars from the relation are needed then abort */
+		if (relation_is_needed(root, joinrelids, removalrel, ignoredrels))
+			return false;
+
+		referencing_vars = NIL;
+		index_vars = NIL;
+		operator_list = NIL;
+
+		/* now populate the lists with the join condition Vars */
+		foreach(lc2, root->eq_classes)
+		{
+			EquivalenceClass *ec = (EquivalenceClass *) lfirst(lc2);
+
+			if (list_length(ec->ec_members) <= 1)
+				continue;
+
+			if (bms_overlap(removalrel->relids, ec->ec_relids) &&
+				bms_overlap(rel->relids, ec->ec_relids))
+			{
+				ListCell *lc3;
+				Var *refvar = NULL;
+				Var *idxvar = NULL;
+
+				/*
+				 * Look at each member of the eclass and try to find a Var from
+				 * each side of the join that we can append to the list of
+				 * columns that should be checked against each foreign key.
+				 *
+				 * The following logic does not allow for join removals to take
+				 * place for foreign keys that have duplicate columns on the
+				 * referencing side of the foreign key, such as:
+				 * (a,a) references (x,y)
+				 * The use case for such a foreign key is likely small enough
+				 * that we needn't bother making this code anymore complex to
+				 * solve. If we find more than 1 Var from any of the rels then
+				 * we'll bail out.
+				 */
+				foreach (lc3, ec->ec_members)
+				{
+					EquivalenceMember *ecm = (EquivalenceMember *) lfirst(lc3);
+
+					Var *var = (Var *) ecm->em_expr;
+
+					if (!IsA(var, Var))
+						continue; /* Ignore Consts */
+
+					if (var->varno == rel->relid)
+					{
+						if (refvar != NULL)
+							return false;
+						refvar = var;
+					}
+
+					else if (var->varno == removalrel->relid)
+					{
+						if (idxvar != NULL)
+							return false;
+						idxvar = var;
+					}
+				}
+
+				if (refvar != NULL && idxvar != NULL)
+				{
+					Oid opno;
+					Oid reloid = root->simple_rte_array[refvar->varno]->relid;
+
+					/*
+					 * We cannot allow the removal to take place if any of the
+					 * columns in the join condition are nullable. This is due
+					 * to the fact that the join condition would end up
+					 * filtering out NULL values for us, but if we remove the
+					 * join, then there's nothing to stop the NULLs getting
+					 * into the resultset.
+					 */
+					if (!get_attnotnull(reloid, refvar->varattno))
+						return false;
+
+					/* grab the correct equality operator for these two vars */
+					opno = select_equality_operator(ec, refvar->vartype, idxvar->vartype);
+
+					if (!OidIsValid(opno))
+						return false;
+
+					referencing_vars = lappend(referencing_vars, refvar);
+					index_vars = lappend(index_vars, idxvar);
+					operator_list = lappend_oid(operator_list, opno);
+				}
+			}
+		}
+
+		/*
+		 * Did we find any conditions? It's ok that we just check 1 of the 3
+		 * lists to see if it's empty here as these will always contain the
+		 * same number of items
+		 */
+		if (referencing_vars != NIL)
+		{
+			if (relation_has_foreign_key_for(root, rel, removalrel,
+				referencing_vars, index_vars, operator_list))
+				return true; /* removalrel can be removed */
+		}
+	}
+
+	return false; /* can't remove join */
+}
+
+/*
+ * leftjoin_is_removable
+ *	  Check whether we need not perform this left join at all, because
  *	  it will just duplicate its left input.
  *
  * This is true for a left join for which the join condition cannot match
@@ -147,7 +450,7 @@ clause_sides_match_join(RestrictInfo *rinfo, Relids outerrelids,
  * above the join.
  */
 static bool
-join_is_removable(PlannerInfo *root, SpecialJoinInfo *sjinfo)
+leftjoin_is_removable(PlannerInfo *root, SpecialJoinInfo *sjinfo)
 {
 	int			innerrelid;
 	RelOptInfo *innerrel;
@@ -155,14 +458,14 @@ join_is_removable(PlannerInfo *root, SpecialJoinInfo *sjinfo)
 	Relids		joinrelids;
 	List	   *clause_list = NIL;
 	ListCell   *l;
-	int			attroff;
+
+	Assert(sjinfo->jointype == JOIN_LEFT);
 
 	/*
-	 * Must be a non-delaying left join to a single baserel, else we aren't
+	 * Must be a non-delaying join to a single baserel, else we aren't
 	 * going to be able to do anything with it.
 	 */
-	if (sjinfo->jointype != JOIN_LEFT ||
-		sjinfo->delay_upper_joins)
+	if (sjinfo->delay_upper_joins)
 		return false;
 
 	if (!bms_get_singleton_member(sjinfo->min_righthand, &innerrelid))
@@ -206,52 +509,9 @@ join_is_removable(PlannerInfo *root, SpecialJoinInfo *sjinfo)
 	/* Compute the relid set for the join we are considering */
 	joinrelids = bms_union(sjinfo->min_lefthand, sjinfo->min_righthand);
 
-	/*
-	 * We can't remove the join if any inner-rel attributes are used above the
-	 * join.
-	 *
-	 * Note that this test only detects use of inner-rel attributes in higher
-	 * join conditions and the target list.  There might be such attributes in
-	 * pushed-down conditions at this join, too.  We check that case below.
-	 *
-	 * As a micro-optimization, it seems better to start with max_attr and
-	 * count down rather than starting with min_attr and counting up, on the
-	 * theory that the system attributes are somewhat less likely to be wanted
-	 * and should be tested last.
-	 */
-	for (attroff = innerrel->max_attr - innerrel->min_attr;
-		 attroff >= 0;
-		 attroff--)
-	{
-		if (!bms_is_subset(innerrel->attr_needed[attroff], joinrelids))
-			return false;
-	}
-
-	/*
-	 * Similarly check that the inner rel isn't needed by any PlaceHolderVars
-	 * that will be used above the join.  We only need to fail if such a PHV
-	 * actually references some inner-rel attributes; but the correct check
-	 * for that is relatively expensive, so we first check against ph_eval_at,
-	 * which must mention the inner rel if the PHV uses any inner-rel attrs as
-	 * non-lateral references.  Note that if the PHV's syntactic scope is just
-	 * the inner rel, we can't drop the rel even if the PHV is variable-free.
-	 */
-	foreach(l, root->placeholder_list)
-	{
-		PlaceHolderInfo *phinfo = (PlaceHolderInfo *) lfirst(l);
-
-		if (bms_is_subset(phinfo->ph_needed, joinrelids))
-			continue;			/* PHV is not used above the join */
-		if (bms_overlap(phinfo->ph_lateral, innerrel->relids))
-			return false;		/* it references innerrel laterally */
-		if (!bms_overlap(phinfo->ph_eval_at, innerrel->relids))
-			continue;			/* it definitely doesn't reference innerrel */
-		if (bms_is_subset(phinfo->ph_eval_at, innerrel->relids))
-			return false;		/* there isn't any other place to eval PHV */
-		if (bms_overlap(pull_varnos((Node *) phinfo->ph_var->phexpr),
-						innerrel->relids))
-			return false;		/* it does reference innerrel */
-	}
+	/* if the relation is referenced in the query then it cannot be removed */
+	if (relation_is_needed(root, joinrelids, innerrel, NULL))
+		return false;
 
 	/*
 	 * Search for mergejoinable clauses that constrain the inner rel against
@@ -368,6 +628,218 @@ join_is_removable(PlannerInfo *root, SpecialJoinInfo *sjinfo)
 	return false;
 }
 
+/*
+ * relation_is_needed
+ *		True if any of the Vars from this relation are required in the query
+ */
+static inline bool
+relation_is_needed(PlannerInfo *root, Relids joinrelids, RelOptInfo *rel, Relids ignoredrels)
+{
+	int		  attroff;
+	ListCell *l;
+
+	/*
+	 * rel is referenced if any of it's attributes are used above the join.
+	 *
+	 * Note that this test only detects use of rel's attributes in higher
+	 * join conditions and the target list.  There might be such attributes in
+	 * pushed-down conditions at this join, too.  We check that case below.
+	 *
+	 * As a micro-optimization, it seems better to start with max_attr and
+	 * count down rather than starting with min_attr and counting up, on the
+	 * theory that the system attributes are somewhat less likely to be wanted
+	 * and should be tested last.
+	 */
+	for (attroff = rel->max_attr - rel->min_attr;
+		 attroff >= 0;
+		 attroff--)
+	{
+		if (!bms_is_subset(bms_difference(rel->attr_needed[attroff], ignoredrels), joinrelids))
+			return true;
+	}
+
+	/*
+	 * Similarly check that rel isn't needed by any PlaceHolderVars that will
+	 * be used above the join.  We only need to fail if such a PHV actually
+	 * references some of rel's attributes; but the correct check for that is
+	 * relatively expensive, so we first check against ph_eval_at, which must
+	 * mention rel if the PHV uses any of-rel's attrs as non-lateral
+	 * references.  Note that if the PHV's syntactic scope is just rel, we
+	 * can't return true even if the PHV is variable-free.
+	 */
+	foreach(l, root->placeholder_list)
+	{
+		PlaceHolderInfo *phinfo = (PlaceHolderInfo *) lfirst(l);
+
+		if (bms_is_subset(phinfo->ph_needed, joinrelids))
+			continue;			/* PHV is not used above the join */
+		if (bms_overlap(phinfo->ph_lateral, rel->relids))
+			return true;		/* it references rel laterally */
+		if (!bms_overlap(phinfo->ph_eval_at, rel->relids))
+			continue;			/* it definitely doesn't reference rel */
+		if (bms_is_subset(phinfo->ph_eval_at, rel->relids))
+			return true;		/* there isn't any other place to eval PHV */
+		if (bms_overlap(pull_varnos((Node *) phinfo->ph_var->phexpr),
+						rel->relids))
+			return true;		/* it does reference rel */
+	}
+
+	return false; /* it does not reference rel */
+}
+
+/*
+ * relation_has_foreign_key_for
+ *	  Checks if rel has a foreign key which references referencedrel with the
+ *	  given list of expressions.
+ *
+ *	For the match to succeed:
+ *	  referencing_vars must match the columns defined in the foreign key.
+ *	  index_vars must match the columns defined in the index for the foreign key.
+ */
+static bool
+relation_has_foreign_key_for(PlannerInfo *root, RelOptInfo *rel,
+			RelOptInfo *referencedrel, List *referencing_vars,
+			List *index_vars, List *operator_list)
+{
+	ListCell *lc;
+	Oid		  refreloid;
+
+	/*
+	 * Look up the Oid of the referenced relation. We only want to look at
+	 * foreign keys on the referencing relation which reference this relation.
+	 */
+	refreloid = root->simple_rte_array[referencedrel->relid]->relid;
+
+	Assert(list_length(referencing_vars) > 0);
+	Assert(list_length(referencing_vars) == list_length(index_vars));
+	Assert(list_length(referencing_vars) == list_length(operator_list));
+
+	/*
+	 * Search through each foreign key on the referencing relation and try
+	 * to find one which references the relation in the join condition. If we
+	 * find one then we'll send the join conditions off to
+	 * expressions_match_foreign_key() to see if they match the foreign key.
+	 */
+	foreach(lc, rel->fklist)
+	{
+		ForeignKeyInfo *fk = (ForeignKeyInfo *) lfirst(lc);
+
+		if (fk->confrelid == refreloid)
+		{
+			if (expressions_match_foreign_key(fk, referencing_vars,
+				index_vars, operator_list))
+				return true;
+		}
+	}
+
+	return false;
+}
+
+/*
+ * expressions_match_foreign_key
+ *		True if the given fkvars, indexvars and operators will match
+ *		exactly 1 record in the referenced relation of the foreign key.
+ *
+ * Note: This function expects fkvars and indexvars to only contain Var types.
+ *		 Expression indexes are not supported by foreign keys.
+ */
+static bool
+expressions_match_foreign_key(ForeignKeyInfo *fk, List *fkvars,
+					List *indexvars, List *operators)
+{
+	ListCell  *lc;
+	ListCell  *lc2;
+	ListCell  *lc3;
+	Bitmapset *allitems;
+	Bitmapset *matcheditems;
+	int		   lstidx;
+	int		   col;
+
+	Assert(list_length(fkvars) == list_length(indexvars));
+	Assert(list_length(fkvars) == list_length(operators));
+
+	/*
+	 * Fast path out if there's not enough conditions to match each column in
+	 * the foreign key. Note that we cannot check that the number of
+	 * expressions are equal here since it would cause any expressions which
+	 * are duplicated not to match.
+	 */
+	if (list_length(fkvars) < fk->conncols)
+		return false;
+
+	/*
+	 * We need to ensure that each foreign key column can be matched to a list
+	 * item, and we need to ensure that each list item can be matched to a
+	 * foreign key column. We do this by looping over each foreign key column
+	 * and checking that we can find an item in the list which matches the
+	 * current column, however this method does not allow us to ensure that no
+	 * additional items exist in the list. We could solve that by performing
+	 * another loop over each list item and check that it matches a foreign key
+	 * column, but that's a bit wasteful. Instead we'll use 2 bitmapsets, one
+	 * to store the 0 based index of each list item, and with the other we'll
+	 * store each list index that we've managed to match. After we're done
+	 * matching we'll just make sure that both bitmapsets are equal.
+	 */
+	allitems = NULL;
+	matcheditems = NULL;
+
+	/*
+	 * Build a bitmapset which contains each 1 based list index. It seems more
+	 * efficient to do this in reverse so that we allocate enough memory for
+	 * the bitmapset on first loop rather than reallocating each time we find
+	 * we need a bit more space.
+	 */
+	for (lstidx = list_length(fkvars) - 1; lstidx >= 0; lstidx--)
+		allitems = bms_add_member(allitems, lstidx);
+
+	for (col = 0; col < fk->conncols; col++)
+	{
+		bool  matched = false;
+
+		lstidx = 0;
+
+		forthree(lc, fkvars, lc2, indexvars, lc3, operators)
+		{
+			Var *expr = (Var *) lfirst(lc);
+			Var *idxexpr = (Var *) lfirst(lc2);
+			Oid  opr = lfirst_oid(lc3);
+
+			Assert(IsA(expr, Var));
+			Assert(IsA(idxexpr, Var));
+
+			/* Does this join qual match up to the current fkey column? */
+			if (fk->conkey[col] == expr->varattno &&
+				fk->confkey[col] == idxexpr->varattno &&
+				equality_ops_are_compatible(opr, fk->conpfeqop[col]))
+			{
+				matched = true;
+
+				/* mark this list item as matched */
+				matcheditems = bms_add_member(matcheditems, lstidx);
+
+				/*
+				 * Don't break here as there may be duplicate expressions
+				 * that we also need to match against.
+				 */
+			}
+			lstidx++;
+		}
+
+		/* punt if there's no match. */
+		if (!matched)
+			return false;
+	}
+
+	/*
+	 * Ensure that we managed to match every item in the list to a foreign key
+	 * column.
+	 */
+	if (!bms_equal(allitems, matcheditems))
+		return false;
+
+	return true; /* matched */
+}
+
 
 /*
  * Remove the target relid from the planner's data structures, having
diff --git a/src/backend/optimizer/plan/createplan.c b/src/backend/optimizer/plan/createplan.c
index 655be81..7540a1d 100644
--- a/src/backend/optimizer/plan/createplan.c
+++ b/src/backend/optimizer/plan/createplan.c
@@ -4676,6 +4676,15 @@ make_lockrows(Plan *lefttree, List *rowMarks, int epqParam)
 	return node;
 }
 
+AlternativePlan *
+make_alternativeplan(List *planlist)
+{
+	AlternativePlan *node = makeNode(AlternativePlan);
+	node->planList = planlist;
+
+	return node;
+}
+
 /*
  * Note: offset_est and count_est are passed in to save having to repeat
  * work already done to estimate the values of the limitOffset and limitCount
diff --git a/src/backend/optimizer/plan/planagg.c b/src/backend/optimizer/plan/planagg.c
index b90c2ef..5cd2ab5 100644
--- a/src/backend/optimizer/plan/planagg.c
+++ b/src/backend/optimizer/plan/planagg.c
@@ -409,6 +409,7 @@ build_minmax_path(PlannerInfo *root, MinMaxAggInfo *mminfo,
 	Path	   *sorted_path;
 	Cost		path_cost;
 	double		path_fraction;
+	List	   *final_rel_list;
 
 	/*----------
 	 * Generate modified query of the form
@@ -478,8 +479,12 @@ build_minmax_path(PlannerInfo *root, MinMaxAggInfo *mminfo,
 	subroot->tuple_fraction = 1.0;
 	subroot->limit_tuples = 1.0;
 
-	final_rel = query_planner(subroot, parse->targetList,
-							  minmax_qp_callback, NULL);
+	final_rel_list = query_planner(subroot, parse->targetList,
+							  minmax_qp_callback, NULL, true);
+
+	Assert(list_length(final_rel_list) ==  1);
+
+	final_rel = (RelOptInfo *) linitial(final_rel_list);
 
 	/*
 	 * Get the best presorted path, that being the one that's cheapest for
diff --git a/src/backend/optimizer/plan/planmain.c b/src/backend/optimizer/plan/planmain.c
index 848df97..6cf5915 100644
--- a/src/backend/optimizer/plan/planmain.c
+++ b/src/backend/optimizer/plan/planmain.c
@@ -34,7 +34,7 @@
  *
  * Since query_planner does not handle the toplevel processing (grouping,
  * sorting, etc) it cannot select the best path by itself.  Instead, it
- * returns the RelOptInfo for the top level of joining, and the caller
+ * returns a list of RelOptInfo for the top level of joining, and the caller
  * (grouping_planner) can choose one of the surviving paths for the rel.
  * Normally it would choose either the rel's cheapest path, or the cheapest
  * path for the desired sort order.
@@ -50,14 +50,23 @@
  * plan.  This value is *not* available at call time, but is computed by
  * qp_callback once we have completed merging the query's equivalence classes.
  * (We cannot construct canonical pathkeys until that's done.)
+ *
+ * Note: during the planning process, the planner may discover optimization
+ * opportunities that may or may not be possible to utiliize during query
+ * execution. In this case the planner will generate 2 plans. 1 for the fully
+ * optimized version, and 1 all purpose plan which will only be used if
+ * conditions are not found to be favourable for the optimized version of the
+ * plan during executor startup.
  */
-RelOptInfo *
+List *
 query_planner(PlannerInfo *root, List *tlist,
-			  query_pathkeys_callback qp_callback, void *qp_extra)
+			  query_pathkeys_callback qp_callback, void *qp_extra,
+			  bool all_purpose_plan_only)
 {
 	Query	   *parse = root->parse;
 	List	   *joinlist;
 	RelOptInfo *final_rel;
+	List	   *final_rel_list = NIL;
 	Index		rti;
 	double		total_pages;
 
@@ -84,7 +93,7 @@ query_planner(PlannerInfo *root, List *tlist,
 		root->canon_pathkeys = NIL;
 		(*qp_callback) (root, qp_extra);
 
-		return final_rel;
+		return lappend(NIL, final_rel);
 	}
 
 	/*
@@ -231,14 +240,37 @@ query_planner(PlannerInfo *root, List *tlist,
 	root->total_table_pages = total_pages;
 
 	/*
-	 * Ready to do the primary planning.
+	 * If the planner found any optimizations that caused the plan not to be
+	 * suitable in all situations, then we must create 2 plans. One will be
+	 * the fully the optimized version and the other will be a general purpose
+	 * plan that will only be used by the executor if any of the required
+	 * conditions for the optimization were not met. Note that we'll only
+	 * generate an optimized plan if the caller didn't specifically request an
+	 * all purpose plan.
 	 */
-	final_rel = make_one_rel(root, joinlist);
+	if (root->glob->suitableFor != PLAN_SUITABILITY_ALL_PURPOSE
+		&& all_purpose_plan_only == false)
+	{
+		/* Generate fully optimized plan, with all removable joins removed */
+		final_rel = make_one_rel(root, joinlist, root->glob->suitableFor);
+
+		/* Check that we got at least one usable path */
+		if (!final_rel || !final_rel->cheapest_total_path ||
+			final_rel->cheapest_total_path->param_info != NULL)
+			elog(ERROR, "failed to construct the join relation");
+
+		final_rel_list = lappend(final_rel_list, final_rel);
+	}
+
+	/* generate an all purpose plan */
+	final_rel = make_one_rel(root, joinlist, PLAN_SUITABILITY_ALL_PURPOSE);
 
 	/* Check that we got at least one usable path */
 	if (!final_rel || !final_rel->cheapest_total_path ||
 		final_rel->cheapest_total_path->param_info != NULL)
 		elog(ERROR, "failed to construct the join relation");
 
-	return final_rel;
+	final_rel_list = lappend(final_rel_list, final_rel);
+
+	return final_rel_list;
 }
diff --git a/src/backend/optimizer/plan/planner.c b/src/backend/optimizer/plan/planner.c
index 9cbbcfb..7ca31e3 100644
--- a/src/backend/optimizer/plan/planner.c
+++ b/src/backend/optimizer/plan/planner.c
@@ -178,6 +178,7 @@ standard_planner(Query *parse, int cursorOptions, ParamListInfo boundParams)
 	glob->lastRowMarkId = 0;
 	glob->transientPlan = false;
 	glob->hasRowSecurity = false;
+	glob->suitableFor = PLAN_SUITABILITY_ALL_PURPOSE;
 
 	/* Determine what fraction of the plan is likely to be scanned */
 	if (cursorOptions & CURSOR_OPT_FAST_PLAN)
@@ -256,6 +257,7 @@ standard_planner(Query *parse, int cursorOptions, ParamListInfo boundParams)
 	result->invalItems = glob->invalItems;
 	result->nParamExec = glob->nParamExec;
 	result->hasRowSecurity = glob->hasRowSecurity;
+	result->suitableFor = glob->suitableFor;
 
 	return result;
 }
@@ -1087,10 +1089,12 @@ grouping_planner(PlannerInfo *root, double tuple_fraction)
 	int64		count_est = 0;
 	double		limit_tuples = -1.0;
 	Plan	   *result_plan;
+	List	   *result_plan_list = NIL;
 	List	   *current_pathkeys;
 	double		dNumGroups = 0;
 	bool		use_hashed_distinct = false;
 	bool		tested_hashed_distinct = false;
+	ListCell   *lc;
 
 	/* Tweak caller-supplied tuple_fraction if have LIMIT/OFFSET */
 	if (parse->limitCount || parse->limitOffset)
@@ -1169,6 +1173,8 @@ grouping_planner(PlannerInfo *root, double tuple_fraction)
 		root->sort_pathkeys = make_pathkeys_for_sortclauses(root,
 															parse->sortClause,
 															tlist);
+
+		result_plan_list = list_make1(result_plan);
 	}
 	else
 	{
@@ -1178,6 +1184,7 @@ grouping_planner(PlannerInfo *root, double tuple_fraction)
 		bool		need_tlist_eval = true;
 		standard_qp_extra qp_extra;
 		RelOptInfo *final_rel;
+		List	   *final_rel_list;
 		Path	   *cheapest_path;
 		Path	   *sorted_path;
 		Path	   *best_path;
@@ -1288,710 +1295,723 @@ grouping_planner(PlannerInfo *root, double tuple_fraction)
 		 * standard_qp_callback) pathkey representations of the query's sort
 		 * clause, distinct clause, etc.
 		 */
-		final_rel = query_planner(root, sub_tlist,
-								  standard_qp_callback, &qp_extra);
-
-		/*
-		 * Extract rowcount and width estimates for use below.
-		 */
-		path_rows = final_rel->rows;
-		path_width = final_rel->width;
+		final_rel_list = query_planner(root, sub_tlist,
+							  standard_qp_callback, &qp_extra, false);
 
-		/*
-		 * If there's grouping going on, estimate the number of result groups.
-		 * We couldn't do this any earlier because it depends on relation size
-		 * estimates that are created within query_planner().
-		 *
-		 * Then convert tuple_fraction to fractional form if it is absolute,
-		 * and if grouping or aggregation is involved, adjust tuple_fraction
-		 * to describe the fraction of the underlying un-aggregated tuples
-		 * that will be fetched.
-		 */
-		dNumGroups = 1;			/* in case not grouping */
-
-		if (parse->groupClause)
+		foreach(lc, final_rel_list)
 		{
-			List	   *groupExprs;
-
-			groupExprs = get_sortgrouplist_exprs(parse->groupClause,
-												 parse->targetList);
-			dNumGroups = estimate_num_groups(root, groupExprs, path_rows);
-
+			final_rel = (RelOptInfo *) lfirst(lc);
 			/*
-			 * In GROUP BY mode, an absolute LIMIT is relative to the number
-			 * of groups not the number of tuples.  If the caller gave us a
-			 * fraction, keep it as-is.  (In both cases, we are effectively
-			 * assuming that all the groups are about the same size.)
+			 * Extract rowcount and width estimates for use below.
 			 */
-			if (tuple_fraction >= 1.0)
-				tuple_fraction /= dNumGroups;
+			path_rows = final_rel->rows;
+			path_width = final_rel->width;
 
 			/*
-			 * If both GROUP BY and ORDER BY are specified, we will need two
-			 * levels of sort --- and, therefore, certainly need to read all
-			 * the tuples --- unless ORDER BY is a subset of GROUP BY.
-			 * Likewise if we have both DISTINCT and GROUP BY, or if we have a
-			 * window specification not compatible with the GROUP BY.
-			 */
-			if (!pathkeys_contained_in(root->sort_pathkeys,
-									   root->group_pathkeys) ||
-				!pathkeys_contained_in(root->distinct_pathkeys,
-									   root->group_pathkeys) ||
-				!pathkeys_contained_in(root->window_pathkeys,
-									   root->group_pathkeys))
-				tuple_fraction = 0.0;
-		}
-		else if (parse->hasAggs || root->hasHavingQual)
-		{
-			/*
-			 * Ungrouped aggregate will certainly want to read all the tuples,
-			 * and it will deliver a single result row (so leave dNumGroups
-			 * set to 1).
-			 */
-			tuple_fraction = 0.0;
-		}
-		else if (parse->distinctClause)
-		{
-			/*
-			 * Since there was no grouping or aggregation, it's reasonable to
-			 * assume the UNIQUE filter has effects comparable to GROUP BY.
-			 * (If DISTINCT is used with grouping, we ignore its effects for
-			 * rowcount estimation purposes; this amounts to assuming the
-			 * grouped rows are distinct already.)
-			 */
-			List	   *distinctExprs;
-
-			distinctExprs = get_sortgrouplist_exprs(parse->distinctClause,
-													parse->targetList);
-			dNumGroups = estimate_num_groups(root, distinctExprs, path_rows);
-
-			/*
-			 * Adjust tuple_fraction the same way as for GROUP BY, too.
-			 */
-			if (tuple_fraction >= 1.0)
-				tuple_fraction /= dNumGroups;
-		}
-		else
-		{
-			/*
-			 * Plain non-grouped, non-aggregated query: an absolute tuple
-			 * fraction can be divided by the number of tuples.
+			 * If there's grouping going on, estimate the number of result groups.
+			 * We couldn't do this any earlier because it depends on relation size
+			 * estimates that are created within query_planner().
+			 *
+			 * Then convert tuple_fraction to fractional form if it is absolute,
+			 * and if grouping or aggregation is involved, adjust tuple_fraction
+			 * to describe the fraction of the underlying un-aggregated tuples
+			 * that will be fetched.
 			 */
-			if (tuple_fraction >= 1.0)
-				tuple_fraction /= path_rows;
-		}
+			dNumGroups = 1;			/* in case not grouping */
 
-		/*
-		 * Pick out the cheapest-total path as well as the cheapest presorted
-		 * path for the requested pathkeys (if there is one).  We should take
-		 * the tuple fraction into account when selecting the cheapest
-		 * presorted path, but not when selecting the cheapest-total path,
-		 * since if we have to sort then we'll have to fetch all the tuples.
-		 * (But there's a special case: if query_pathkeys is NIL, meaning
-		 * order doesn't matter, then the "cheapest presorted" path will be
-		 * the cheapest overall for the tuple fraction.)
-		 */
-		cheapest_path = final_rel->cheapest_total_path;
-
-		sorted_path =
-			get_cheapest_fractional_path_for_pathkeys(final_rel->pathlist,
-													  root->query_pathkeys,
-													  NULL,
-													  tuple_fraction);
+			if (parse->groupClause)
+			{
+				List	   *groupExprs;
 
-		/* Don't consider same path in both guises; just wastes effort */
-		if (sorted_path == cheapest_path)
-			sorted_path = NULL;
+				groupExprs = get_sortgrouplist_exprs(parse->groupClause,
+													 parse->targetList);
+				dNumGroups = estimate_num_groups(root, groupExprs, path_rows);
 
-		/*
-		 * Forget about the presorted path if it would be cheaper to sort the
-		 * cheapest-total path.  Here we need consider only the behavior at
-		 * the tuple_fraction point.  Also, limit_tuples is only relevant if
-		 * not grouping/aggregating, so use root->limit_tuples in the
-		 * cost_sort call.
-		 */
-		if (sorted_path)
-		{
-			Path		sort_path;		/* dummy for result of cost_sort */
+				/*
+				 * In GROUP BY mode, an absolute LIMIT is relative to the number
+				 * of groups not the number of tuples.  If the caller gave us a
+				 * fraction, keep it as-is.  (In both cases, we are effectively
+				 * assuming that all the groups are about the same size.)
+				 */
+				if (tuple_fraction >= 1.0)
+					tuple_fraction /= dNumGroups;
 
-			if (root->query_pathkeys == NIL ||
-				pathkeys_contained_in(root->query_pathkeys,
-									  cheapest_path->pathkeys))
-			{
-				/* No sort needed for cheapest path */
-				sort_path.startup_cost = cheapest_path->startup_cost;
-				sort_path.total_cost = cheapest_path->total_cost;
+				/*
+				 * If both GROUP BY and ORDER BY are specified, we will need two
+				 * levels of sort --- and, therefore, certainly need to read all
+				 * the tuples --- unless ORDER BY is a subset of GROUP BY.
+				 * Likewise if we have both DISTINCT and GROUP BY, or if we have a
+				 * window specification not compatible with the GROUP BY.
+				 */
+				if (!pathkeys_contained_in(root->sort_pathkeys,
+										   root->group_pathkeys) ||
+					!pathkeys_contained_in(root->distinct_pathkeys,
+										   root->group_pathkeys) ||
+					!pathkeys_contained_in(root->window_pathkeys,
+										   root->group_pathkeys))
+					tuple_fraction = 0.0;
 			}
-			else
+			else if (parse->hasAggs || root->hasHavingQual)
 			{
-				/* Figure cost for sorting */
-				cost_sort(&sort_path, root, root->query_pathkeys,
-						  cheapest_path->total_cost,
-						  path_rows, path_width,
-						  0.0, work_mem, root->limit_tuples);
+				/*
+				 * Ungrouped aggregate will certainly want to read all the tuples,
+				 * and it will deliver a single result row (so leave dNumGroups
+				 * set to 1).
+				 */
+				tuple_fraction = 0.0;
 			}
-
-			if (compare_fractional_path_costs(sorted_path, &sort_path,
-											  tuple_fraction) > 0)
+			else if (parse->distinctClause)
 			{
-				/* Presorted path is a loser */
-				sorted_path = NULL;
-			}
-		}
+				/*
+				 * Since there was no grouping or aggregation, it's reasonable to
+				 * assume the UNIQUE filter has effects comparable to GROUP BY.
+				 * (If DISTINCT is used with grouping, we ignore its effects for
+				 * rowcount estimation purposes; this amounts to assuming the
+				 * grouped rows are distinct already.)
+				 */
+				List	   *distinctExprs;
 
-		/*
-		 * Consider whether we want to use hashing instead of sorting.
-		 */
-		if (parse->groupClause)
-		{
-			/*
-			 * If grouping, decide whether to use sorted or hashed grouping.
-			 */
-			use_hashed_grouping =
-				choose_hashed_grouping(root,
-									   tuple_fraction, limit_tuples,
-									   path_rows, path_width,
-									   cheapest_path, sorted_path,
-									   dNumGroups, &agg_costs);
-			/* Also convert # groups to long int --- but 'ware overflow! */
-			numGroups = (long) Min(dNumGroups, (double) LONG_MAX);
-		}
-		else if (parse->distinctClause && sorted_path &&
-				 !root->hasHavingQual && !parse->hasAggs && !activeWindows)
-		{
-			/*
-			 * We'll reach the DISTINCT stage without any intermediate
-			 * processing, so figure out whether we will want to hash or not
-			 * so we can choose whether to use cheapest or sorted path.
-			 */
-			use_hashed_distinct =
-				choose_hashed_distinct(root,
-									   tuple_fraction, limit_tuples,
-									   path_rows, path_width,
-									   cheapest_path->startup_cost,
-									   cheapest_path->total_cost,
-									   sorted_path->startup_cost,
-									   sorted_path->total_cost,
-									   sorted_path->pathkeys,
-									   dNumGroups);
-			tested_hashed_distinct = true;
-		}
+				distinctExprs = get_sortgrouplist_exprs(parse->distinctClause,
+														parse->targetList);
+				dNumGroups = estimate_num_groups(root, distinctExprs, path_rows);
 
-		/*
-		 * Select the best path.  If we are doing hashed grouping, we will
-		 * always read all the input tuples, so use the cheapest-total path.
-		 * Otherwise, the comparison above is correct.
-		 */
-		if (use_hashed_grouping || use_hashed_distinct || !sorted_path)
-			best_path = cheapest_path;
-		else
-			best_path = sorted_path;
+				/*
+				 * Adjust tuple_fraction the same way as for GROUP BY, too.
+				 */
+				if (tuple_fraction >= 1.0)
+					tuple_fraction /= dNumGroups;
+			}
+			else
+			{
+				/*
+				 * Plain non-grouped, non-aggregated query: an absolute tuple
+				 * fraction can be divided by the number of tuples.
+				 */
+				if (tuple_fraction >= 1.0)
+					tuple_fraction /= path_rows;
+			}
 
-		/*
-		 * Check to see if it's possible to optimize MIN/MAX aggregates. If
-		 * so, we will forget all the work we did so far to choose a "regular"
-		 * path ... but we had to do it anyway to be able to tell which way is
-		 * cheaper.
-		 */
-		result_plan = optimize_minmax_aggregates(root,
-												 tlist,
-												 &agg_costs,
-												 best_path);
-		if (result_plan != NULL)
-		{
-			/*
-			 * optimize_minmax_aggregates generated the full plan, with the
-			 * right tlist, and it has no sort order.
-			 */
-			current_pathkeys = NIL;
-		}
-		else
-		{
 			/*
-			 * Normal case --- create a plan according to query_planner's
-			 * results.
+			 * Pick out the cheapest-total path as well as the cheapest presorted
+			 * path for the requested pathkeys (if there is one).  We should take
+			 * the tuple fraction into account when selecting the cheapest
+			 * presorted path, but not when selecting the cheapest-total path,
+			 * since if we have to sort then we'll have to fetch all the tuples.
+			 * (But there's a special case: if query_pathkeys is NIL, meaning
+			 * order doesn't matter, then the "cheapest presorted" path will be
+			 * the cheapest overall for the tuple fraction.)
 			 */
-			bool		need_sort_for_grouping = false;
+			cheapest_path = final_rel->cheapest_total_path;
 
-			result_plan = create_plan(root, best_path);
-			current_pathkeys = best_path->pathkeys;
+			sorted_path =
+				get_cheapest_fractional_path_for_pathkeys(final_rel->pathlist,
+														  root->query_pathkeys,
+														  NULL,
+														  tuple_fraction);
 
-			/* Detect if we'll need an explicit sort for grouping */
-			if (parse->groupClause && !use_hashed_grouping &&
-			  !pathkeys_contained_in(root->group_pathkeys, current_pathkeys))
-			{
-				need_sort_for_grouping = true;
-
-				/*
-				 * Always override create_plan's tlist, so that we don't sort
-				 * useless data from a "physical" tlist.
-				 */
-				need_tlist_eval = true;
-			}
+			/* Don't consider same path in both guises; just wastes effort */
+			if (sorted_path == cheapest_path)
+				sorted_path = NULL;
 
 			/*
-			 * create_plan returns a plan with just a "flat" tlist of required
-			 * Vars.  Usually we need to insert the sub_tlist as the tlist of
-			 * the top plan node.  However, we can skip that if we determined
-			 * that whatever create_plan chose to return will be good enough.
+			 * Forget about the presorted path if it would be cheaper to sort the
+			 * cheapest-total path.  Here we need consider only the behavior at
+			 * the tuple_fraction point.  Also, limit_tuples is only relevant if
+			 * not grouping/aggregating, so use root->limit_tuples in the
+			 * cost_sort call.
 			 */
-			if (need_tlist_eval)
+			if (sorted_path)
 			{
-				/*
-				 * If the top-level plan node is one that cannot do expression
-				 * evaluation and its existing target list isn't already what
-				 * we need, we must insert a Result node to project the
-				 * desired tlist.
-				 */
-				if (!is_projection_capable_plan(result_plan) &&
-					!tlist_same_exprs(sub_tlist, result_plan->targetlist))
+				Path		sort_path;		/* dummy for result of cost_sort */
+
+				if (root->query_pathkeys == NIL ||
+					pathkeys_contained_in(root->query_pathkeys,
+										  cheapest_path->pathkeys))
 				{
-					result_plan = (Plan *) make_result(root,
-													   sub_tlist,
-													   NULL,
-													   result_plan);
+					/* No sort needed for cheapest path */
+					sort_path.startup_cost = cheapest_path->startup_cost;
+					sort_path.total_cost = cheapest_path->total_cost;
 				}
 				else
 				{
-					/*
-					 * Otherwise, just replace the subplan's flat tlist with
-					 * the desired tlist.
-					 */
-					result_plan->targetlist = sub_tlist;
+					/* Figure cost for sorting */
+					cost_sort(&sort_path, root, root->query_pathkeys,
+							  cheapest_path->total_cost,
+							  path_rows, path_width,
+							  0.0, work_mem, root->limit_tuples);
 				}
 
+				if (compare_fractional_path_costs(sorted_path, &sort_path,
+												  tuple_fraction) > 0)
+				{
+					/* Presorted path is a loser */
+					sorted_path = NULL;
+				}
+			}
+
+			/*
+			 * Consider whether we want to use hashing instead of sorting.
+			 */
+			if (parse->groupClause)
+			{
 				/*
-				 * Also, account for the cost of evaluation of the sub_tlist.
-				 * See comments for add_tlist_costs_to_plan() for more info.
+				 * If grouping, decide whether to use sorted or hashed grouping.
 				 */
-				add_tlist_costs_to_plan(root, result_plan, sub_tlist);
+				use_hashed_grouping =
+					choose_hashed_grouping(root,
+										   tuple_fraction, limit_tuples,
+										   path_rows, path_width,
+										   cheapest_path, sorted_path,
+										   dNumGroups, &agg_costs);
+				/* Also convert # groups to long int --- but 'ware overflow! */
+				numGroups = (long) Min(dNumGroups, (double) LONG_MAX);
 			}
-			else
+			else if (parse->distinctClause && sorted_path &&
+					 !root->hasHavingQual && !parse->hasAggs && !activeWindows)
 			{
 				/*
-				 * Since we're using create_plan's tlist and not the one
-				 * make_subplanTargetList calculated, we have to refigure any
-				 * grouping-column indexes make_subplanTargetList computed.
+				 * We'll reach the DISTINCT stage without any intermediate
+				 * processing, so figure out whether we will want to hash or not
+				 * so we can choose whether to use cheapest or sorted path.
 				 */
-				locate_grouping_columns(root, tlist, result_plan->targetlist,
-										groupColIdx);
+				use_hashed_distinct =
+					choose_hashed_distinct(root,
+										   tuple_fraction, limit_tuples,
+										   path_rows, path_width,
+										   cheapest_path->startup_cost,
+										   cheapest_path->total_cost,
+										   sorted_path->startup_cost,
+										   sorted_path->total_cost,
+										   sorted_path->pathkeys,
+										   dNumGroups);
+				tested_hashed_distinct = true;
 			}
 
 			/*
-			 * Insert AGG or GROUP node if needed, plus an explicit sort step
-			 * if necessary.
-			 *
-			 * HAVING clause, if any, becomes qual of the Agg or Group node.
+			 * Select the best path.  If we are doing hashed grouping, we will
+			 * always read all the input tuples, so use the cheapest-total path.
+			 * Otherwise, the comparison above is correct.
 			 */
-			if (use_hashed_grouping)
+			if (use_hashed_grouping || use_hashed_distinct || !sorted_path)
+				best_path = cheapest_path;
+			else
+				best_path = sorted_path;
+
+			/*
+			 * Check to see if it's possible to optimize MIN/MAX aggregates. If
+			 * so, we will forget all the work we did so far to choose a "regular"
+			 * path ... but we had to do it anyway to be able to tell which way is
+			 * cheaper.
+			 */
+			result_plan = optimize_minmax_aggregates(root,
+													 tlist,
+													 &agg_costs,
+													 best_path);
+			if (result_plan != NULL)
 			{
-				/* Hashed aggregate plan --- no sort needed */
-				result_plan = (Plan *) make_agg(root,
-												tlist,
-												(List *) parse->havingQual,
-												AGG_HASHED,
-												&agg_costs,
-												numGroupCols,
-												groupColIdx,
-									extract_grouping_ops(parse->groupClause),
-												numGroups,
-												result_plan);
-				/* Hashed aggregation produces randomly-ordered results */
+				/*
+				 * optimize_minmax_aggregates generated the full plan, with the
+				 * right tlist, and it has no sort order.
+				 */
 				current_pathkeys = NIL;
 			}
-			else if (parse->hasAggs)
+			else
 			{
-				/* Plain aggregate plan --- sort if needed */
-				AggStrategy aggstrategy;
+				/*
+				 * Normal case --- create a plan according to query_planner's
+				 * results.
+				 */
+				bool		need_sort_for_grouping = false;
+
+				result_plan = create_plan(root, best_path);
+				current_pathkeys = best_path->pathkeys;
 
-				if (parse->groupClause)
+				/* Detect if we'll need an explicit sort for grouping */
+				if (parse->groupClause && !use_hashed_grouping &&
+				  !pathkeys_contained_in(root->group_pathkeys, current_pathkeys))
 				{
-					if (need_sort_for_grouping)
+					need_sort_for_grouping = true;
+
+					/*
+					 * Always override create_plan's tlist, so that we don't sort
+					 * useless data from a "physical" tlist.
+					 */
+					need_tlist_eval = true;
+				}
+
+				/*
+				 * create_plan returns a plan with just a "flat" tlist of required
+				 * Vars.  Usually we need to insert the sub_tlist as the tlist of
+				 * the top plan node.  However, we can skip that if we determined
+				 * that whatever create_plan chose to return will be good enough.
+				 */
+				if (need_tlist_eval)
+				{
+					/*
+					 * If the top-level plan node is one that cannot do expression
+					 * evaluation and its existing target list isn't already what
+					 * we need, we must insert a Result node to project the
+					 * desired tlist.
+					 */
+					if (!is_projection_capable_plan(result_plan) &&
+						!tlist_same_exprs(sub_tlist, result_plan->targetlist))
 					{
-						result_plan = (Plan *)
-							make_sort_from_groupcols(root,
-													 parse->groupClause,
-													 groupColIdx,
-													 result_plan);
-						current_pathkeys = root->group_pathkeys;
+						result_plan = (Plan *) make_result(root,
+														   sub_tlist,
+														   NULL,
+														   result_plan);
+					}
+					else
+					{
+						/*
+						 * Otherwise, just replace the subplan's flat tlist with
+						 * the desired tlist.
+						 */
+						result_plan->targetlist = sub_tlist;
 					}
-					aggstrategy = AGG_SORTED;
 
 					/*
-					 * The AGG node will not change the sort ordering of its
-					 * groups, so current_pathkeys describes the result too.
+					 * Also, account for the cost of evaluation of the sub_tlist.
+					 * See comments for add_tlist_costs_to_plan() for more info.
 					 */
+					add_tlist_costs_to_plan(root, result_plan, sub_tlist);
 				}
 				else
 				{
-					aggstrategy = AGG_PLAIN;
-					/* Result will be only one row anyway; no sort order */
-					current_pathkeys = NIL;
+					/*
+					 * Since we're using create_plan's tlist and not the one
+					 * make_subplanTargetList calculated, we have to refigure any
+					 * grouping-column indexes make_subplanTargetList computed.
+					 */
+					locate_grouping_columns(root, tlist, result_plan->targetlist,
+											groupColIdx);
 				}
 
-				result_plan = (Plan *) make_agg(root,
-												tlist,
-												(List *) parse->havingQual,
-												aggstrategy,
-												&agg_costs,
-												numGroupCols,
-												groupColIdx,
-									extract_grouping_ops(parse->groupClause),
-												numGroups,
-												result_plan);
-			}
-			else if (parse->groupClause)
-			{
 				/*
-				 * GROUP BY without aggregation, so insert a group node (plus
-				 * the appropriate sort node, if necessary).
+				 * Insert AGG or GROUP node if needed, plus an explicit sort step
+				 * if necessary.
 				 *
-				 * Add an explicit sort if we couldn't make the path come out
-				 * the way the GROUP node needs it.
+				 * HAVING clause, if any, becomes qual of the Agg or Group node.
 				 */
-				if (need_sort_for_grouping)
+				if (use_hashed_grouping)
 				{
-					result_plan = (Plan *)
-						make_sort_from_groupcols(root,
-												 parse->groupClause,
-												 groupColIdx,
-												 result_plan);
-					current_pathkeys = root->group_pathkeys;
+					/* Hashed aggregate plan --- no sort needed */
+					result_plan = (Plan *) make_agg(root,
+													tlist,
+													(List *) parse->havingQual,
+													AGG_HASHED,
+													&agg_costs,
+													numGroupCols,
+													groupColIdx,
+										extract_grouping_ops(parse->groupClause),
+													numGroups,
+													result_plan);
+					/* Hashed aggregation produces randomly-ordered results */
+					current_pathkeys = NIL;
 				}
+				else if (parse->hasAggs)
+				{
+					/* Plain aggregate plan --- sort if needed */
+					AggStrategy aggstrategy;
 
-				result_plan = (Plan *) make_group(root,
-												  tlist,
-												  (List *) parse->havingQual,
-												  numGroupCols,
-												  groupColIdx,
-									extract_grouping_ops(parse->groupClause),
-												  dNumGroups,
-												  result_plan);
-				/* The Group node won't change sort ordering */
-			}
-			else if (root->hasHavingQual)
-			{
-				/*
-				 * No aggregates, and no GROUP BY, but we have a HAVING qual.
-				 * This is a degenerate case in which we are supposed to emit
-				 * either 0 or 1 row depending on whether HAVING succeeds.
-				 * Furthermore, there cannot be any variables in either HAVING
-				 * or the targetlist, so we actually do not need the FROM
-				 * table at all!  We can just throw away the plan-so-far and
-				 * generate a Result node.  This is a sufficiently unusual
-				 * corner case that it's not worth contorting the structure of
-				 * this routine to avoid having to generate the plan in the
-				 * first place.
-				 */
-				result_plan = (Plan *) make_result(root,
-												   tlist,
-												   parse->havingQual,
-												   NULL);
-			}
-		}						/* end of non-minmax-aggregate case */
-
-		/*
-		 * Since each window function could require a different sort order, we
-		 * stack up a WindowAgg node for each window, with sort steps between
-		 * them as needed.
-		 */
-		if (activeWindows)
-		{
-			List	   *window_tlist;
-			ListCell   *l;
+					if (parse->groupClause)
+					{
+						if (need_sort_for_grouping)
+						{
+							result_plan = (Plan *)
+								make_sort_from_groupcols(root,
+														 parse->groupClause,
+														 groupColIdx,
+														 result_plan);
+							current_pathkeys = root->group_pathkeys;
+						}
+						aggstrategy = AGG_SORTED;
+
+						/*
+						 * The AGG node will not change the sort ordering of its
+						 * groups, so current_pathkeys describes the result too.
+						 */
+					}
+					else
+					{
+						aggstrategy = AGG_PLAIN;
+						/* Result will be only one row anyway; no sort order */
+						current_pathkeys = NIL;
+					}
 
-			/*
-			 * If the top-level plan node is one that cannot do expression
-			 * evaluation, we must insert a Result node to project the desired
-			 * tlist.  (In some cases this might not really be required, but
-			 * it's not worth trying to avoid it.  In particular, think not to
-			 * skip adding the Result if the initial window_tlist matches the
-			 * top-level plan node's output, because we might change the tlist
-			 * inside the following loop.)	Note that on second and subsequent
-			 * passes through the following loop, the top-level node will be a
-			 * WindowAgg which we know can project; so we only need to check
-			 * once.
-			 */
-			if (!is_projection_capable_plan(result_plan))
-			{
-				result_plan = (Plan *) make_result(root,
-												   NIL,
-												   NULL,
-												   result_plan);
-			}
+					result_plan = (Plan *) make_agg(root,
+													tlist,
+													(List *) parse->havingQual,
+													aggstrategy,
+													&agg_costs,
+													numGroupCols,
+													groupColIdx,
+										extract_grouping_ops(parse->groupClause),
+													numGroups,
+													result_plan);
+				}
+				else if (parse->groupClause)
+				{
+					/*
+					 * GROUP BY without aggregation, so insert a group node (plus
+					 * the appropriate sort node, if necessary).
+					 *
+					 * Add an explicit sort if we couldn't make the path come out
+					 * the way the GROUP node needs it.
+					 */
+					if (need_sort_for_grouping)
+					{
+						result_plan = (Plan *)
+							make_sort_from_groupcols(root,
+													 parse->groupClause,
+													 groupColIdx,
+													 result_plan);
+						current_pathkeys = root->group_pathkeys;
+					}
 
-			/*
-			 * The "base" targetlist for all steps of the windowing process is
-			 * a flat tlist of all Vars and Aggs needed in the result.  (In
-			 * some cases we wouldn't need to propagate all of these all the
-			 * way to the top, since they might only be needed as inputs to
-			 * WindowFuncs.  It's probably not worth trying to optimize that
-			 * though.)  We also add window partitioning and sorting
-			 * expressions to the base tlist, to ensure they're computed only
-			 * once at the bottom of the stack (that's critical for volatile
-			 * functions).  As we climb up the stack, we'll add outputs for
-			 * the WindowFuncs computed at each level.
-			 */
-			window_tlist = make_windowInputTargetList(root,
+					result_plan = (Plan *) make_group(root,
 													  tlist,
-													  activeWindows);
+													  (List *) parse->havingQual,
+													  numGroupCols,
+													  groupColIdx,
+										extract_grouping_ops(parse->groupClause),
+													  dNumGroups,
+													  result_plan);
+					/* The Group node won't change sort ordering */
+				}
+				else if (root->hasHavingQual)
+				{
+					/*
+					 * No aggregates, and no GROUP BY, but we have a HAVING qual.
+					 * This is a degenerate case in which we are supposed to emit
+					 * either 0 or 1 row depending on whether HAVING succeeds.
+					 * Furthermore, there cannot be any variables in either HAVING
+					 * or the targetlist, so we actually do not need the FROM
+					 * table at all!  We can just throw away the plan-so-far and
+					 * generate a Result node.  This is a sufficiently unusual
+					 * corner case that it's not worth contorting the structure of
+					 * this routine to avoid having to generate the plan in the
+					 * first place.
+					 */
+					result_plan = (Plan *) make_result(root,
+													   tlist,
+													   parse->havingQual,
+													   NULL);
+				}
+			}						/* end of non-minmax-aggregate case */
 
 			/*
-			 * The copyObject steps here are needed to ensure that each plan
-			 * node has a separately modifiable tlist.  (XXX wouldn't a
-			 * shallow list copy do for that?)
+			 * Since each window function could require a different sort order, we
+			 * stack up a WindowAgg node for each window, with sort steps between
+			 * them as needed.
 			 */
-			result_plan->targetlist = (List *) copyObject(window_tlist);
-
-			foreach(l, activeWindows)
+			if (activeWindows)
 			{
-				WindowClause *wc = (WindowClause *) lfirst(l);
-				List	   *window_pathkeys;
-				int			partNumCols;
-				AttrNumber *partColIdx;
-				Oid		   *partOperators;
-				int			ordNumCols;
-				AttrNumber *ordColIdx;
-				Oid		   *ordOperators;
-
-				window_pathkeys = make_pathkeys_for_window(root,
-														   wc,
-														   tlist);
+				List	   *window_tlist;
+				ListCell   *l;
 
 				/*
-				 * This is a bit tricky: we build a sort node even if we don't
-				 * really have to sort.  Even when no explicit sort is needed,
-				 * we need to have suitable resjunk items added to the input
-				 * plan's tlist for any partitioning or ordering columns that
-				 * aren't plain Vars.  (In theory, make_windowInputTargetList
-				 * should have provided all such columns, but let's not assume
-				 * that here.)	Furthermore, this way we can use existing
-				 * infrastructure to identify which input columns are the
-				 * interesting ones.
+				 * If the top-level plan node is one that cannot do expression
+				 * evaluation, we must insert a Result node to project the desired
+				 * tlist.  (In some cases this might not really be required, but
+				 * it's not worth trying to avoid it.  In particular, think not to
+				 * skip adding the Result if the initial window_tlist matches the
+				 * top-level plan node's output, because we might change the tlist
+				 * inside the following loop.)	Note that on second and subsequent
+				 * passes through the following loop, the top-level node will be a
+				 * WindowAgg which we know can project; so we only need to check
+				 * once.
 				 */
-				if (window_pathkeys)
-				{
-					Sort	   *sort_plan;
-
-					sort_plan = make_sort_from_pathkeys(root,
-														result_plan,
-														window_pathkeys,
-														-1.0);
-					if (!pathkeys_contained_in(window_pathkeys,
-											   current_pathkeys))
-					{
-						/* we do indeed need to sort */
-						result_plan = (Plan *) sort_plan;
-						current_pathkeys = window_pathkeys;
-					}
-					/* In either case, extract the per-column information */
-					get_column_info_for_window(root, wc, tlist,
-											   sort_plan->numCols,
-											   sort_plan->sortColIdx,
-											   &partNumCols,
-											   &partColIdx,
-											   &partOperators,
-											   &ordNumCols,
-											   &ordColIdx,
-											   &ordOperators);
-				}
-				else
+				if (!is_projection_capable_plan(result_plan))
 				{
-					/* empty window specification, nothing to sort */
-					partNumCols = 0;
-					partColIdx = NULL;
-					partOperators = NULL;
-					ordNumCols = 0;
-					ordColIdx = NULL;
-					ordOperators = NULL;
+					result_plan = (Plan *) make_result(root,
+													   NIL,
+													   NULL,
+													   result_plan);
 				}
 
-				if (lnext(l))
-				{
-					/* Add the current WindowFuncs to the running tlist */
-					window_tlist = add_to_flat_tlist(window_tlist,
-										   wflists->windowFuncs[wc->winref]);
-				}
-				else
+				/*
+				 * The "base" targetlist for all steps of the windowing process is
+				 * a flat tlist of all Vars and Aggs needed in the result.  (In
+				 * some cases we wouldn't need to propagate all of these all the
+				 * way to the top, since they might only be needed as inputs to
+				 * WindowFuncs.  It's probably not worth trying to optimize that
+				 * though.)  We also add window partitioning and sorting
+				 * expressions to the base tlist, to ensure they're computed only
+				 * once at the bottom of the stack (that's critical for volatile
+				 * functions).  As we climb up the stack, we'll add outputs for
+				 * the WindowFuncs computed at each level.
+				 */
+				window_tlist = make_windowInputTargetList(root,
+														  tlist,
+														  activeWindows);
+
+				/*
+				 * The copyObject steps here are needed to ensure that each plan
+				 * node has a separately modifiable tlist.  (XXX wouldn't a
+				 * shallow list copy do for that?)
+				 */
+				result_plan->targetlist = (List *) copyObject(window_tlist);
+
+				foreach(l, activeWindows)
 				{
-					/* Install the original tlist in the topmost WindowAgg */
-					window_tlist = tlist;
-				}
+					WindowClause *wc = (WindowClause *) lfirst(l);
+					List	   *window_pathkeys;
+					int			partNumCols;
+					AttrNumber *partColIdx;
+					Oid		   *partOperators;
+					int			ordNumCols;
+					AttrNumber *ordColIdx;
+					Oid		   *ordOperators;
+
+					window_pathkeys = make_pathkeys_for_window(root,
+															   wc,
+															   tlist);
+
+					/*
+					 * This is a bit tricky: we build a sort node even if we don't
+					 * really have to sort.  Even when no explicit sort is needed,
+					 * we need to have suitable resjunk items added to the input
+					 * plan's tlist for any partitioning or ordering columns that
+					 * aren't plain Vars.  (In theory, make_windowInputTargetList
+					 * should have provided all such columns, but let's not assume
+					 * that here.)	Furthermore, this way we can use existing
+					 * infrastructure to identify which input columns are the
+					 * interesting ones.
+					 */
+					if (window_pathkeys)
+					{
+						Sort	   *sort_plan;
+
+						sort_plan = make_sort_from_pathkeys(root,
+															result_plan,
+															window_pathkeys,
+															-1.0);
+						if (!pathkeys_contained_in(window_pathkeys,
+												   current_pathkeys))
+						{
+							/* we do indeed need to sort */
+							result_plan = (Plan *) sort_plan;
+							current_pathkeys = window_pathkeys;
+						}
+						/* In either case, extract the per-column information */
+						get_column_info_for_window(root, wc, tlist,
+												   sort_plan->numCols,
+												   sort_plan->sortColIdx,
+												   &partNumCols,
+												   &partColIdx,
+												   &partOperators,
+												   &ordNumCols,
+												   &ordColIdx,
+												   &ordOperators);
+					}
+					else
+					{
+						/* empty window specification, nothing to sort */
+						partNumCols = 0;
+						partColIdx = NULL;
+						partOperators = NULL;
+						ordNumCols = 0;
+						ordColIdx = NULL;
+						ordOperators = NULL;
+					}
 
-				/* ... and make the WindowAgg plan node */
-				result_plan = (Plan *)
-					make_windowagg(root,
-								   (List *) copyObject(window_tlist),
-								   wflists->windowFuncs[wc->winref],
-								   wc->winref,
-								   partNumCols,
-								   partColIdx,
-								   partOperators,
-								   ordNumCols,
-								   ordColIdx,
-								   ordOperators,
-								   wc->frameOptions,
-								   wc->startOffset,
-								   wc->endOffset,
-								   result_plan);
+					if (lnext(l))
+					{
+						/* Add the current WindowFuncs to the running tlist */
+						window_tlist = add_to_flat_tlist(window_tlist,
+											   wflists->windowFuncs[wc->winref]);
+					}
+					else
+					{
+						/* Install the original tlist in the topmost WindowAgg */
+						window_tlist = tlist;
+					}
+
+					/* ... and make the WindowAgg plan node */
+					result_plan = (Plan *)
+						make_windowagg(root,
+									   (List *) copyObject(window_tlist),
+									   wflists->windowFuncs[wc->winref],
+									   wc->winref,
+									   partNumCols,
+									   partColIdx,
+									   partOperators,
+									   ordNumCols,
+									   ordColIdx,
+									   ordOperators,
+									   wc->frameOptions,
+									   wc->startOffset,
+									   wc->endOffset,
+									   result_plan);
+				}
 			}
-		}
+
+			result_plan_list = lappend(result_plan_list, result_plan);
+		}						 /* foreach final_rel_list */
 	}							/* end of if (setOperations) */
 
-	/*
-	 * If there is a DISTINCT clause, add the necessary node(s).
-	 */
-	if (parse->distinctClause)
+	foreach(lc, result_plan_list)
 	{
-		double		dNumDistinctRows;
-		long		numDistinctRows;
+		result_plan = (Plan *) lfirst(lc);
 
 		/*
-		 * If there was grouping or aggregation, use the current number of
-		 * rows as the estimated number of DISTINCT rows (ie, assume the
-		 * result was already mostly unique).  If not, use the number of
-		 * distinct-groups calculated previously.
+		 * If there is a DISTINCT clause, add the necessary node(s).
 		 */
-		if (parse->groupClause || root->hasHavingQual || parse->hasAggs)
-			dNumDistinctRows = result_plan->plan_rows;
-		else
-			dNumDistinctRows = dNumGroups;
-
-		/* Also convert to long int --- but 'ware overflow! */
-		numDistinctRows = (long) Min(dNumDistinctRows, (double) LONG_MAX);
-
-		/* Choose implementation method if we didn't already */
-		if (!tested_hashed_distinct)
+		if (parse->distinctClause)
 		{
-			/*
-			 * At this point, either hashed or sorted grouping will have to
-			 * work from result_plan, so we pass that as both "cheapest" and
-			 * "sorted".
-			 */
-			use_hashed_distinct =
-				choose_hashed_distinct(root,
-									   tuple_fraction, limit_tuples,
-									   result_plan->plan_rows,
-									   result_plan->plan_width,
-									   result_plan->startup_cost,
-									   result_plan->total_cost,
-									   result_plan->startup_cost,
-									   result_plan->total_cost,
-									   current_pathkeys,
-									   dNumDistinctRows);
-		}
+			double		dNumDistinctRows;
+			long		numDistinctRows;
 
-		if (use_hashed_distinct)
-		{
-			/* Hashed aggregate plan --- no sort needed */
-			result_plan = (Plan *) make_agg(root,
-											result_plan->targetlist,
-											NIL,
-											AGG_HASHED,
-											NULL,
-										  list_length(parse->distinctClause),
-								 extract_grouping_cols(parse->distinctClause,
-													result_plan->targetlist),
-								 extract_grouping_ops(parse->distinctClause),
-											numDistinctRows,
-											result_plan);
-			/* Hashed aggregation produces randomly-ordered results */
-			current_pathkeys = NIL;
-		}
-		else
-		{
 			/*
-			 * Use a Unique node to implement DISTINCT.  Add an explicit sort
-			 * if we couldn't make the path come out the way the Unique node
-			 * needs it.  If we do have to sort, always sort by the more
-			 * rigorous of DISTINCT and ORDER BY, to avoid a second sort
-			 * below.  However, for regular DISTINCT, don't sort now if we
-			 * don't have to --- sorting afterwards will likely be cheaper,
-			 * and also has the possibility of optimizing via LIMIT.  But for
-			 * DISTINCT ON, we *must* force the final sort now, else it won't
-			 * have the desired behavior.
+			 * If there was grouping or aggregation, use the current number of
+			 * rows as the estimated number of DISTINCT rows (ie, assume the
+			 * result was already mostly unique).  If not, use the number of
+			 * distinct-groups calculated previously.
 			 */
-			List	   *needed_pathkeys;
-
-			if (parse->hasDistinctOn &&
-				list_length(root->distinct_pathkeys) <
-				list_length(root->sort_pathkeys))
-				needed_pathkeys = root->sort_pathkeys;
+			if (parse->groupClause || root->hasHavingQual || parse->hasAggs)
+				dNumDistinctRows = result_plan->plan_rows;
 			else
-				needed_pathkeys = root->distinct_pathkeys;
+				dNumDistinctRows = dNumGroups;
+
+			/* Also convert to long int --- but 'ware overflow! */
+			numDistinctRows = (long) Min(dNumDistinctRows, (double) LONG_MAX);
+
+			/* Choose implementation method if we didn't already */
+			if (!tested_hashed_distinct)
+			{
+				/*
+				 * At this point, either hashed or sorted grouping will have to
+				 * work from result_plan, so we pass that as both "cheapest" and
+				 * "sorted".
+				 */
+				use_hashed_distinct =
+					choose_hashed_distinct(root,
+										   tuple_fraction, limit_tuples,
+										   result_plan->plan_rows,
+										   result_plan->plan_width,
+										   result_plan->startup_cost,
+										   result_plan->total_cost,
+										   result_plan->startup_cost,
+										   result_plan->total_cost,
+										   current_pathkeys,
+										   dNumDistinctRows);
+			}
 
-			if (!pathkeys_contained_in(needed_pathkeys, current_pathkeys))
+			if (use_hashed_distinct)
+			{
+				/* Hashed aggregate plan --- no sort needed */
+				result_plan = (Plan *) make_agg(root,
+												result_plan->targetlist,
+												NIL,
+												AGG_HASHED,
+												NULL,
+											  list_length(parse->distinctClause),
+									 extract_grouping_cols(parse->distinctClause,
+														result_plan->targetlist),
+									 extract_grouping_ops(parse->distinctClause),
+												numDistinctRows,
+												result_plan);
+				/* Hashed aggregation produces randomly-ordered results */
+				current_pathkeys = NIL;
+			}
+			else
 			{
-				if (list_length(root->distinct_pathkeys) >=
+				/*
+				 * Use a Unique node to implement DISTINCT.  Add an explicit sort
+				 * if we couldn't make the path come out the way the Unique node
+				 * needs it.  If we do have to sort, always sort by the more
+				 * rigorous of DISTINCT and ORDER BY, to avoid a second sort
+				 * below.  However, for regular DISTINCT, don't sort now if we
+				 * don't have to --- sorting afterwards will likely be cheaper,
+				 * and also has the possibility of optimizing via LIMIT.  But for
+				 * DISTINCT ON, we *must* force the final sort now, else it won't
+				 * have the desired behavior.
+				 */
+				List	   *needed_pathkeys;
+
+				if (parse->hasDistinctOn &&
+					list_length(root->distinct_pathkeys) <
 					list_length(root->sort_pathkeys))
-					current_pathkeys = root->distinct_pathkeys;
+					needed_pathkeys = root->sort_pathkeys;
 				else
+					needed_pathkeys = root->distinct_pathkeys;
+
+				if (!pathkeys_contained_in(needed_pathkeys, current_pathkeys))
 				{
-					current_pathkeys = root->sort_pathkeys;
-					/* Assert checks that parser didn't mess up... */
-					Assert(pathkeys_contained_in(root->distinct_pathkeys,
-												 current_pathkeys));
+					if (list_length(root->distinct_pathkeys) >=
+						list_length(root->sort_pathkeys))
+						current_pathkeys = root->distinct_pathkeys;
+					else
+					{
+						current_pathkeys = root->sort_pathkeys;
+						/* Assert checks that parser didn't mess up... */
+						Assert(pathkeys_contained_in(root->distinct_pathkeys,
+													 current_pathkeys));
+					}
+
+					result_plan = (Plan *) make_sort_from_pathkeys(root,
+																   result_plan,
+																current_pathkeys,
+																   -1.0);
 				}
 
+				result_plan = (Plan *) make_unique(result_plan,
+												   parse->distinctClause);
+				result_plan->plan_rows = dNumDistinctRows;
+				/* The Unique node won't change sort ordering */
+			}
+		}
+
+		/*
+		 * If ORDER BY was given and we were not able to make the plan come out in
+		 * the right order, add an explicit sort step.
+		 */
+		if (parse->sortClause)
+		{
+			if (!pathkeys_contained_in(root->sort_pathkeys, current_pathkeys))
+			{
 				result_plan = (Plan *) make_sort_from_pathkeys(root,
 															   result_plan,
-															current_pathkeys,
-															   -1.0);
+															 root->sort_pathkeys,
+															   limit_tuples);
+				current_pathkeys = root->sort_pathkeys;
 			}
-
-			result_plan = (Plan *) make_unique(result_plan,
-											   parse->distinctClause);
-			result_plan->plan_rows = dNumDistinctRows;
-			/* The Unique node won't change sort ordering */
 		}
-	}
 
-	/*
-	 * If ORDER BY was given and we were not able to make the plan come out in
-	 * the right order, add an explicit sort step.
-	 */
-	if (parse->sortClause)
-	{
-		if (!pathkeys_contained_in(root->sort_pathkeys, current_pathkeys))
+		/*
+		 * If there is a FOR [KEY] UPDATE/SHARE clause, add the LockRows node.
+		 * (Note: we intentionally test parse->rowMarks not root->rowMarks here.
+		 * If there are only non-locking rowmarks, they should be handled by the
+		 * ModifyTable node instead.)
+		 */
+		if (parse->rowMarks)
 		{
-			result_plan = (Plan *) make_sort_from_pathkeys(root,
-														   result_plan,
-														 root->sort_pathkeys,
-														   limit_tuples);
-			current_pathkeys = root->sort_pathkeys;
-		}
-	}
+			result_plan = (Plan *) make_lockrows(result_plan,
+												 root->rowMarks,
+												 SS_assign_special_param(root));
 
-	/*
-	 * If there is a FOR [KEY] UPDATE/SHARE clause, add the LockRows node.
-	 * (Note: we intentionally test parse->rowMarks not root->rowMarks here.
-	 * If there are only non-locking rowmarks, they should be handled by the
-	 * ModifyTable node instead.)
-	 */
-	if (parse->rowMarks)
-	{
-		result_plan = (Plan *) make_lockrows(result_plan,
-											 root->rowMarks,
-											 SS_assign_special_param(root));
+			/*
+			 * The result can no longer be assumed sorted, since locking might
+			 * cause the sort key columns to be replaced with new values.
+			 */
+			current_pathkeys = NIL;
+		}
 
 		/*
-		 * The result can no longer be assumed sorted, since locking might
-		 * cause the sort key columns to be replaced with new values.
+		 * Finally, if there is a LIMIT/OFFSET clause, add the LIMIT node.
 		 */
-		current_pathkeys = NIL;
-	}
+		if (limit_needed(parse))
+		{
+			result_plan = (Plan *) make_limit(result_plan,
+											  parse->limitOffset,
+											  parse->limitCount,
+											  offset_est,
+											  count_est);
+		}
 
-	/*
-	 * Finally, if there is a LIMIT/OFFSET clause, add the LIMIT node.
-	 */
-	if (limit_needed(parse))
-	{
-		result_plan = (Plan *) make_limit(result_plan,
-										  parse->limitOffset,
-										  parse->limitCount,
-										  offset_est,
-										  count_est);
-	}
+		lfirst(lc) = result_plan;
+	} /* foreach all_plans */
 
 	/*
 	 * Return the actual output ordering in query_pathkeys for possible use by
@@ -1999,7 +2019,16 @@ grouping_planner(PlannerInfo *root, double tuple_fraction)
 	 */
 	root->query_pathkeys = current_pathkeys;
 
-	return result_plan;
+	/* if there is only one plan, then just return that plan */
+	if (list_length(result_plan_list) == 1)
+		return (Plan *) linitial(result_plan_list);
+
+	/*
+	 * Otherwise we'd better add an AlternativePlan node to allow the executor
+	 * to decide which plan to use.
+	 */
+	else
+		return (Plan *) make_alternativeplan(result_plan_list);
 }
 
 /*
diff --git a/src/backend/optimizer/plan/setrefs.c b/src/backend/optimizer/plan/setrefs.c
index 7703946..c0b7a34 100644
--- a/src/backend/optimizer/plan/setrefs.c
+++ b/src/backend/optimizer/plan/setrefs.c
@@ -435,6 +435,17 @@ set_plan_refs(PlannerInfo *root, Plan *plan, int rtoffset)
 	 */
 	switch (nodeTag(plan))
 	{
+		case T_AlternativePlan:
+			{
+				AlternativePlan *aplan = (AlternativePlan *) plan;
+				ListCell *lc;
+				foreach(lc, aplan->planList)
+				{
+					Plan *plan = (Plan *) lfirst(lc);
+					set_plan_refs(root, plan, rtoffset);
+				}
+			}
+			break;
 		case T_SeqScan:
 			{
 				SeqScan    *splan = (SeqScan *) plan;
diff --git a/src/backend/optimizer/util/plancat.c b/src/backend/optimizer/util/plancat.c
index 265c865..855bc96 100644
--- a/src/backend/optimizer/util/plancat.c
+++ b/src/backend/optimizer/util/plancat.c
@@ -25,7 +25,9 @@
 #include "access/transam.h"
 #include "access/xlog.h"
 #include "catalog/catalog.h"
+#include "catalog/pg_constraint.h"
 #include "catalog/heap.h"
+#include "catalog/pg_type.h"
 #include "foreign/fdwapi.h"
 #include "miscadmin.h"
 #include "nodes/makefuncs.h"
@@ -38,6 +40,7 @@
 #include "parser/parsetree.h"
 #include "rewrite/rewriteManip.h"
 #include "storage/bufmgr.h"
+#include "utils/fmgroids.h"
 #include "utils/lsyscache.h"
 #include "utils/rel.h"
 #include "utils/snapmgr.h"
@@ -89,6 +92,12 @@ get_relation_info(PlannerInfo *root, Oid relationObjectId, bool inhparent,
 	Relation	relation;
 	bool		hasindex;
 	List	   *indexinfos = NIL;
+	List	   *fkinfos = NIL;
+	Relation	fkeyRel;
+	Relation	fkeyRelIdx;
+	ScanKeyData fkeyScankey;
+	SysScanDesc fkeyScan;
+	HeapTuple	tuple;
 
 	/*
 	 * We need not lock the relation since it was already locked, either by
@@ -384,6 +393,111 @@ get_relation_info(PlannerInfo *root, Oid relationObjectId, bool inhparent,
 
 	heap_close(relation, NoLock);
 
+	/* load foreign key constraints */
+	ScanKeyInit(&fkeyScankey,
+				Anum_pg_constraint_conrelid,
+				BTEqualStrategyNumber, F_OIDEQ,
+				ObjectIdGetDatum(relationObjectId));
+
+	fkeyRel = heap_open(ConstraintRelationId, AccessShareLock);
+	fkeyRelIdx = index_open(ConstraintRelidIndexId, AccessShareLock);
+	fkeyScan = systable_beginscan_ordered(fkeyRel, fkeyRelIdx, NULL, 1, &fkeyScankey);
+
+	while ((tuple = systable_getnext_ordered(fkeyScan, ForwardScanDirection)) != NULL)
+	{
+		Form_pg_constraint con = (Form_pg_constraint) GETSTRUCT(tuple);
+		ForeignKeyInfo *fkinfo;
+		Datum		adatum;
+		bool		isNull;
+		ArrayType  *arr;
+		int			nelements;
+
+		/* skip if not a foreign key */
+		if (con->contype != CONSTRAINT_FOREIGN)
+			continue;
+
+		/* we're not interested unless the fkey has been validated */
+		if (!con->convalidated)
+			continue;
+
+		fkinfo = (ForeignKeyInfo *) palloc(sizeof(ForeignKeyInfo));
+		fkinfo->conindid = con->conindid;
+		fkinfo->confrelid = con->confrelid;
+		fkinfo->convalidated = con->convalidated;
+		fkinfo->conrelid = con->conrelid;
+		fkinfo->confupdtype = con->confupdtype;
+		fkinfo->confdeltype = con->confdeltype;
+		fkinfo->confmatchtype = con->confmatchtype;
+
+		adatum = heap_getattr(tuple, Anum_pg_constraint_conkey,
+							RelationGetDescr(fkeyRel), &isNull);
+
+		if (isNull)
+			elog(ERROR, "null conkey for constraint %u",
+				HeapTupleGetOid(tuple));
+
+		arr = DatumGetArrayTypeP(adatum);		/* ensure not toasted */
+		nelements = ARR_DIMS(arr)[0];
+		if (ARR_NDIM(arr) != 1 ||
+			nelements < 0 ||
+			ARR_HASNULL(arr) ||
+			ARR_ELEMTYPE(arr) != INT2OID)
+			elog(ERROR, "conkey is not a 1-D smallint array");
+
+		fkinfo->conkey = (int16 *) ARR_DATA_PTR(arr);
+		fkinfo->conncols = nelements;
+
+		adatum = heap_getattr(tuple, Anum_pg_constraint_confkey,
+							RelationGetDescr(fkeyRel), &isNull);
+
+		if (isNull)
+			elog(ERROR, "null confkey for constraint %u",
+				HeapTupleGetOid(tuple));
+
+		arr = DatumGetArrayTypeP(adatum);		/* ensure not toasted */
+		nelements = ARR_DIMS(arr)[0];
+
+		if (ARR_NDIM(arr) != 1 ||
+			nelements < 0 ||
+			ARR_HASNULL(arr) ||
+			ARR_ELEMTYPE(arr) != INT2OID)
+			elog(ERROR, "confkey is not a 1-D smallint array");
+
+		/* sanity check */
+		if (nelements != fkinfo->conncols)
+			elog(ERROR, "number of confkey elements does not equal conkey elements");
+
+		fkinfo->confkey = (int16 *) ARR_DATA_PTR(arr);
+		adatum = heap_getattr(tuple, Anum_pg_constraint_conpfeqop,
+							RelationGetDescr(fkeyRel), &isNull);
+
+		if (isNull)
+			elog(ERROR, "null conpfeqop for constraint %u",
+				HeapTupleGetOid(tuple));
+
+		arr = DatumGetArrayTypeP(adatum);		/* ensure not toasted */
+		nelements = ARR_DIMS(arr)[0];
+
+		if (ARR_NDIM(arr) != 1 ||
+			nelements < 0 ||
+			ARR_HASNULL(arr) ||
+			ARR_ELEMTYPE(arr) != OIDOID)
+			elog(ERROR, "conpfeqop is not a 1-D smallint array");
+
+		/* sanity check */
+		if (nelements != fkinfo->conncols)
+			elog(ERROR, "number of conpfeqop elements does not equal conkey elements");
+
+		fkinfo->conpfeqop = (Oid *) ARR_DATA_PTR(arr);
+
+		fkinfos = lappend(fkinfos, fkinfo);
+	}
+
+	rel->fklist = fkinfos;
+	systable_endscan_ordered(fkeyScan);
+	index_close(fkeyRelIdx, AccessShareLock);
+	heap_close(fkeyRel, AccessShareLock);
+
 	/*
 	 * Allow a plugin to editorialize on the info we obtained from the
 	 * catalogs.  Actions might include altering the assumed relation size,
diff --git a/src/backend/optimizer/util/relnode.c b/src/backend/optimizer/util/relnode.c
index 8cfbea0..0be29e6 100644
--- a/src/backend/optimizer/util/relnode.c
+++ b/src/backend/optimizer/util/relnode.c
@@ -115,6 +115,7 @@ build_simple_rel(PlannerInfo *root, int relid, RelOptKind reloptkind)
 	rel->lateral_relids = NULL;
 	rel->lateral_referencers = NULL;
 	rel->indexlist = NIL;
+	rel->fklist = NIL;
 	rel->pages = 0;
 	rel->tuples = 0;
 	rel->allvisfrac = 0;
@@ -127,6 +128,7 @@ build_simple_rel(PlannerInfo *root, int relid, RelOptKind reloptkind)
 	rel->baserestrictcost.startup = 0;
 	rel->baserestrictcost.per_tuple = 0;
 	rel->joininfo = NIL;
+	rel->removal_flags = PLAN_SUITABILITY_ALL_PURPOSE;
 	rel->has_eclass_joins = false;
 
 	/* Check type of rtable entry */
@@ -377,6 +379,7 @@ build_join_rel(PlannerInfo *root,
 	joinrel->lateral_relids = NULL;
 	joinrel->lateral_referencers = NULL;
 	joinrel->indexlist = NIL;
+	joinrel->fklist = NIL;
 	joinrel->pages = 0;
 	joinrel->tuples = 0;
 	joinrel->allvisfrac = 0;
@@ -389,6 +392,7 @@ build_join_rel(PlannerInfo *root,
 	joinrel->baserestrictcost.startup = 0;
 	joinrel->baserestrictcost.per_tuple = 0;
 	joinrel->joininfo = NIL;
+	joinrel->removal_flags = PLAN_SUITABILITY_ALL_PURPOSE;
 	joinrel->has_eclass_joins = false;
 
 	/*
diff --git a/src/backend/utils/cache/lsyscache.c b/src/backend/utils/cache/lsyscache.c
index 818c2f6..115e398 100644
--- a/src/backend/utils/cache/lsyscache.c
+++ b/src/backend/utils/cache/lsyscache.c
@@ -916,6 +916,33 @@ get_atttypetypmodcoll(Oid relid, AttrNumber attnum,
 	ReleaseSysCache(tp);
 }
 
+/*
+ * get_attnotnull
+ *
+ *		Given the relation id and the attribute number,
+ *		return the "attnotnull" field from the attribute relation.
+ */
+bool
+get_attnotnull(Oid relid, AttrNumber attnum)
+{
+	HeapTuple	tp;
+
+	tp = SearchSysCache2(ATTNUM,
+						 ObjectIdGetDatum(relid),
+						 Int16GetDatum(attnum));
+	if (HeapTupleIsValid(tp))
+	{
+		Form_pg_attribute att_tup = (Form_pg_attribute) GETSTRUCT(tp);
+		bool		result;
+
+		result = att_tup->attnotnull;
+		ReleaseSysCache(tp);
+		return result;
+	}
+	else
+		return false;
+}
+
 /*				---------- COLLATION CACHE ----------					 */
 
 /*
diff --git a/src/include/commands/trigger.h b/src/include/commands/trigger.h
index d0c0dcc..2ae3ea0 100644
--- a/src/include/commands/trigger.h
+++ b/src/include/commands/trigger.h
@@ -181,6 +181,7 @@ extern void ExecBSTruncateTriggers(EState *estate,
 extern void ExecASTruncateTriggers(EState *estate,
 					   ResultRelInfo *relinfo);
 
+extern bool AfterTriggerQueueIsEmpty(void);
 extern void AfterTriggerBeginXact(void);
 extern void AfterTriggerBeginQuery(void);
 extern void AfterTriggerEndQuery(EState *estate);
diff --git a/src/include/executor/nodeAlternativePlan.h b/src/include/executor/nodeAlternativePlan.h
new file mode 100644
index 0000000..092f4ef
--- /dev/null
+++ b/src/include/executor/nodeAlternativePlan.h
@@ -0,0 +1,25 @@
+/*-------------------------------------------------------------------------
+ *
+ * nodeAppend.h
+ *
+ *
+ *
+ * Portions Copyright (c) 1996-2015, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ * src/include/executor/nodeAlternativePlan.h
+ *
+ *-------------------------------------------------------------------------
+ */
+#ifndef NODEALTERNATIVEPLAN_H
+#define NODEALTERNATIVEPLAN_H
+
+#include "nodes/execnodes.h"
+
+extern PlanState *ExecInitAlternativePlan(AlternativePlan *node,
+						EState *estate, int eflags);
+/*
+ * Note that this node is only ever seen during initialization of a plan and
+ * it has no state type.
+ */
+#endif   /* NODEALTERNATIVEPLAN_H */
diff --git a/src/include/nodes/nodes.h b/src/include/nodes/nodes.h
index 97ef0fc..668d426 100644
--- a/src/include/nodes/nodes.h
+++ b/src/include/nodes/nodes.h
@@ -77,6 +77,7 @@ typedef enum NodeTag
 	T_SetOp,
 	T_LockRows,
 	T_Limit,
+	T_AlternativePlan,
 	/* these aren't subclasses of Plan: */
 	T_NestLoopParam,
 	T_PlanRowMark,
diff --git a/src/include/nodes/parsenodes.h b/src/include/nodes/parsenodes.h
index b1dfa85..3018256 100644
--- a/src/include/nodes/parsenodes.h
+++ b/src/include/nodes/parsenodes.h
@@ -734,6 +734,10 @@ typedef enum RTEKind
 	RTE_CTE						/* common table expr (WITH list element) */
 } RTEKind;
 
+/* Bit flags to mark suitability of plans */
+#define PLAN_SUITABILITY_ALL_PURPOSE		0
+#define PLAN_SUITABILITY_FK_TRIGGER_EMPTY	1
+
 typedef struct RangeTblEntry
 {
 	NodeTag		type;
diff --git a/src/include/nodes/plannodes.h b/src/include/nodes/plannodes.h
index 316c9ce..a3d3127 100644
--- a/src/include/nodes/plannodes.h
+++ b/src/include/nodes/plannodes.h
@@ -70,8 +70,11 @@ typedef struct PlannedStmt
 
 	int			nParamExec;		/* number of PARAM_EXEC Params used */
 
+	int			suitableFor; /* under which conditions can this plan be used */
+
 	bool		hasRowSecurity;	/* row security applied? */
 
+
 } PlannedStmt;
 
 /* macro for fetching the Plan associated with a SubPlan node */
@@ -767,6 +770,20 @@ typedef struct LockRows
 	int			epqParam;		/* ID of Param for EvalPlanQual re-eval */
 } LockRows;
 
+
+/* ----------------
+ *		alternative plan node
+ *
+ * Stores a list of alternative plans and one
+ * all purpose plan.
+ * ----------------
+ */
+typedef struct AlternativePlan
+{
+	Plan		plan;
+	List	   *planList;
+} AlternativePlan;
+
 /* ----------------
  *		limit node
  *
diff --git a/src/include/nodes/relation.h b/src/include/nodes/relation.h
index 6845a40..d94339f 100644
--- a/src/include/nodes/relation.h
+++ b/src/include/nodes/relation.h
@@ -95,6 +95,8 @@ typedef struct PlannerGlobal
 
 	int			nParamExec;		/* number of PARAM_EXEC Params used */
 
+	int			suitableFor; /* under which conditions can this plan be used */
+
 	Index		lastPHId;		/* highest PlaceHolderVar ID assigned */
 
 	Index		lastRowMarkId;	/* highest PlanRowMark ID assigned */
@@ -103,6 +105,7 @@ typedef struct PlannerGlobal
 
 	bool		hasRowSecurity;	/* row security applied? */
 
+
 } PlannerGlobal;
 
 /* macro for fetching the Plan associated with a SubPlan node */
@@ -359,6 +362,8 @@ typedef struct PlannerInfo
  *		lateral_referencers - relids of rels that reference this one laterally
  *		indexlist - list of IndexOptInfo nodes for relation's indexes
  *					(always NIL if it's not a table)
+ *		fklist - list of ForeignKeyInfo's for relation's foreign key
+ *					constraints. (always NIL if it's not a table)
  *		pages - number of disk pages in relation (zero if not a table)
  *		tuples - number of tuples in relation (not considering restrictions)
  *		allvisfrac - fraction of disk pages that are marked all-visible
@@ -452,6 +457,7 @@ typedef struct RelOptInfo
 	Relids		lateral_relids; /* minimum parameterization of rel */
 	Relids		lateral_referencers;	/* rels that reference me laterally */
 	List	   *indexlist;		/* list of IndexOptInfo */
+	List	   *fklist;			/* list of ForeignKeyInfo */
 	BlockNumber pages;			/* size estimates derived from pg_class */
 	double		tuples;
 	double		allvisfrac;
@@ -469,6 +475,8 @@ typedef struct RelOptInfo
 	QualCost	baserestrictcost;		/* cost of evaluating the above */
 	List	   *joininfo;		/* RestrictInfo structures for join clauses
 								 * involving this rel */
+	int			removal_flags;		/* it may be possible to not bother joining
+									 * this relation at all */
 	bool		has_eclass_joins;		/* T means joininfo is incomplete */
 } RelOptInfo;
 
@@ -542,6 +550,51 @@ typedef struct IndexOptInfo
 	bool		amhasgetbitmap; /* does AM have amgetbitmap interface? */
 } IndexOptInfo;
 
+/*
+ * ForeignKeyInfo
+ *		Used to store pg_constraint records for foreign key constraints for use
+ *		by the planner.
+ *
+ *		conindid - The index which supports the foreign key
+ *
+ *		confrelid - The relation that is referenced by this foreign key
+ *
+ *		convalidated - True if the foreign key has been validated.
+ *
+ *		conrelid - The Oid of the relation that the foreign key belongs to
+ *
+ *		confupdtype - ON UPDATE action for when the referenced table is updated
+ *
+ *		confdeltype - ON DELETE action, controls what to do when a record is
+ *					deleted from the referenced table.
+ *
+ *		confmatchtype - foreign key match type, e.g MATCH FULL, MATCH PARTIAL
+ *
+ *		conncols - Number of columns defined in the foreign key
+ *
+ *		conkey - An array of conncols elements to store the varattno of the
+ *					columns on the referencing side of the foreign key
+ *
+ *		confkey - An array of conncols elements to store the varattno of the
+ *					columns on the referenced side of the foreign key
+ *
+ *		conpfeqop - An array of conncols elements to store the operators for
+ *					PK = FK comparisons
+ */
+typedef struct ForeignKeyInfo
+{
+	Oid			conindid;		/* index supporting this constraint */
+	Oid			confrelid;		/* relation referenced by foreign key */
+	bool		convalidated;	/* constraint has been validated? */
+	Oid			conrelid;		/* relation this constraint constrains */
+	char		confupdtype;	/* foreign key's ON UPDATE action */
+	char		confdeltype;	/* foreign key's ON DELETE action */
+	char		confmatchtype;	/* foreign key's match type */
+	int			conncols;		/* number of columns references */
+	int16	   *conkey;			/* Columns of conrelid that the constraint applies to */
+	int16	   *confkey;		/* columns of confrelid that foreign key references */
+	Oid		   *conpfeqop;		/* Operator list for comparing PK to FK */
+} ForeignKeyInfo;
 
 /*
  * EquivalenceClasses
diff --git a/src/include/optimizer/paths.h b/src/include/optimizer/paths.h
index 6cad92e..7b040fa 100644
--- a/src/include/optimizer/paths.h
+++ b/src/include/optimizer/paths.h
@@ -37,7 +37,8 @@ typedef RelOptInfo *(*join_search_hook_type) (PlannerInfo *root,
 extern PGDLLIMPORT join_search_hook_type join_search_hook;
 
 
-extern RelOptInfo *make_one_rel(PlannerInfo *root, List *joinlist);
+extern RelOptInfo *make_one_rel(PlannerInfo *root, List *joinlist,
+								int removal_flags);
 extern RelOptInfo *standard_join_search(PlannerInfo *root, int levels_needed,
 					 List *initial_rels);
 
@@ -119,6 +120,8 @@ extern List *generate_join_implied_equalities(PlannerInfo *root,
 								 Relids join_relids,
 								 Relids outer_relids,
 								 RelOptInfo *inner_rel);
+extern Oid select_equality_operator(EquivalenceClass *ec, Oid lefttype,
+								 Oid righttype);
 extern bool exprs_known_equal(PlannerInfo *root, Node *item1, Node *item2);
 extern void add_child_rel_equivalences(PlannerInfo *root,
 						   AppendRelInfo *appinfo,
diff --git a/src/include/optimizer/planmain.h b/src/include/optimizer/planmain.h
index 082f7d7..7bcd93a 100644
--- a/src/include/optimizer/planmain.h
+++ b/src/include/optimizer/planmain.h
@@ -27,8 +27,9 @@ typedef void (*query_pathkeys_callback) (PlannerInfo *root, void *extra);
 /*
  * prototypes for plan/planmain.c
  */
-extern RelOptInfo *query_planner(PlannerInfo *root, List *tlist,
-			  query_pathkeys_callback qp_callback, void *qp_extra);
+extern List *query_planner(PlannerInfo *root, List *tlist,
+			  query_pathkeys_callback qp_callback, void *qp_extra,
+			  bool all_purpose_plan_only);
 
 /*
  * prototypes for plan/planagg.c
@@ -73,6 +74,7 @@ extern Group *make_group(PlannerInfo *root, List *tlist, List *qual,
 extern Plan *materialize_finished_plan(Plan *subplan);
 extern Unique *make_unique(Plan *lefttree, List *distinctList);
 extern LockRows *make_lockrows(Plan *lefttree, List *rowMarks, int epqParam);
+extern AlternativePlan *make_alternativeplan(List *planlist);
 extern Limit *make_limit(Plan *lefttree, Node *limitOffset, Node *limitCount,
 		   int64 offset_est, int64 count_est);
 extern SetOp *make_setop(SetOpCmd cmd, SetOpStrategy strategy, Plan *lefttree,
diff --git a/src/include/utils/lsyscache.h b/src/include/utils/lsyscache.h
index 2f5ede1..14e64fc 100644
--- a/src/include/utils/lsyscache.h
+++ b/src/include/utils/lsyscache.h
@@ -68,6 +68,7 @@ extern Oid	get_atttype(Oid relid, AttrNumber attnum);
 extern int32 get_atttypmod(Oid relid, AttrNumber attnum);
 extern void get_atttypetypmodcoll(Oid relid, AttrNumber attnum,
 					  Oid *typid, int32 *typmod, Oid *collid);
+extern bool get_attnotnull(Oid relid, AttrNumber attnum);
 extern char *get_collation_name(Oid colloid);
 extern char *get_constraint_name(Oid conoid);
 extern Oid	get_opclass_family(Oid opclass);
diff --git a/src/test/regress/expected/join.out b/src/test/regress/expected/join.out
index 2501184..e485554 100644
--- a/src/test/regress/expected/join.out
+++ b/src/test/regress/expected/join.out
@@ -3276,6 +3276,171 @@ select i8.* from int8_tbl i8 left join (select f1 from int4_tbl group by f1) i4
 (1 row)
 
 rollback;
+begin work;
+create temp table c (
+  id int primary key
+);
+create temp table b (
+  id int primary key,
+  c_id int not null,
+  val int not null,
+  constraint b_c_id_fkey foreign key (c_id) references c deferrable
+);
+create temp table a (
+  id int primary key,
+  b_id int not null,
+  constraint a_b_id_fkey foreign key (b_id) references b deferrable
+);
+insert into c (id) values(1);
+insert into b (id,c_id,val) values(2,1,10);
+insert into a (id,b_id) values(3,2);
+-- this should remove inner join to b
+explain (costs off)
+select a.* from a inner join b on a.b_id = b.id;
+  QUERY PLAN   
+---------------
+ Seq Scan on a
+(1 row)
+
+-- this should remove inner join to b and c
+explain (costs off)
+select a.* from a inner join b on a.b_id = b.id inner join c on b.c_id = c.id;
+  QUERY PLAN   
+---------------
+ Seq Scan on a
+(1 row)
+
+-- Ensure all of the target entries have their proper aliases.
+select a.* from a inner join b on a.b_id = b.id inner join c on b.c_id = c.id;
+ id | b_id 
+----+------
+  3 |    2
+(1 row)
+
+-- change order of tables in query, this should generate the same plan as above.
+explain (costs off)
+select a.* from c inner join b on c.id = b.c_id inner join a on a.b_id = b.id;
+  QUERY PLAN   
+---------------
+ Seq Scan on a
+(1 row)
+
+-- inner join can't be removed due to b columns in the target list
+explain (costs off)
+select * from a inner join b on a.b_id = b.id;
+          QUERY PLAN          
+------------------------------
+ Hash Join
+   Hash Cond: (a.b_id = b.id)
+   ->  Seq Scan on a
+   ->  Hash
+         ->  Seq Scan on b
+(5 rows)
+
+-- this should not remove inner join to b due to quals restricting results from b
+explain (costs off)
+select a.* from a inner join b on a.b_id = b.id where b.val = 10;
+            QUERY PLAN            
+----------------------------------
+ Hash Join
+   Hash Cond: (a.b_id = b.id)
+   ->  Seq Scan on a
+   ->  Hash
+         ->  Seq Scan on b
+               Filter: (val = 10)
+(6 rows)
+
+-- this should not remove join to b
+explain (costs off)
+select a.* from a inner join b on a.b_id = b.id where b.val = b.id;
+            QUERY PLAN            
+----------------------------------
+ Hash Join
+   Hash Cond: (a.b_id = b.id)
+   ->  Seq Scan on a
+   ->  Hash
+         ->  Seq Scan on b
+               Filter: (id = val)
+(6 rows)
+
+-- this should not remove the join, no foreign key exists between a.id and b.id
+explain (costs off)
+select a.* from a inner join b on a.id = b.id;
+         QUERY PLAN         
+----------------------------
+ Hash Join
+   Hash Cond: (a.id = b.id)
+   ->  Seq Scan on a
+   ->  Hash
+         ->  Seq Scan on b
+(5 rows)
+
+-- ensure a left joined rel can't remove an inner joined rel
+explain (costs off)
+select a.* from b left join a on b.id = a.b_id;
+          QUERY PLAN          
+------------------------------
+ Hash Right Join
+   Hash Cond: (a.b_id = b.id)
+   ->  Seq Scan on a
+   ->  Hash
+         ->  Seq Scan on b
+(5 rows)
+
+-- Ensure we remove b, but don't try and remove c. c has no join condition.
+explain (costs off)
+select a.* from a inner join b on a.b_id = b.id cross join c;
+        QUERY PLAN         
+---------------------------
+ Nested Loop
+   ->  Seq Scan on c
+   ->  Materialize
+         ->  Seq Scan on a
+(4 rows)
+
+set constraints b_c_id_fkey deferred;
+-- join should be removed.
+explain (costs off)
+select b.* from b inner join c on b.c_id = c.id;
+  QUERY PLAN   
+---------------
+ Seq Scan on b
+(1 row)
+
+prepare ab as select b.* from b inner join c on b.c_id = c.id;
+explain (costs off)
+execute ab;
+  QUERY PLAN   
+---------------
+ Seq Scan on b
+(1 row)
+
+-- perform an update which will cause some pending fk triggers to be added
+update c set id = 2 where id=1;
+-- ensure inner join is no longer removed.
+explain (costs off)
+select b.* from b inner join c on b.c_id = c.id;
+          QUERY PLAN          
+------------------------------
+ Hash Join
+   Hash Cond: (b.c_id = c.id)
+   ->  Seq Scan on b
+   ->  Hash
+         ->  Seq Scan on c
+(5 rows)
+
+explain (costs off)
+execute ab;
+          QUERY PLAN          
+------------------------------
+ Hash Join
+   Hash Cond: (b.c_id = c.id)
+   ->  Seq Scan on b
+   ->  Hash
+         ->  Seq Scan on c
+(5 rows)
+
+rollback;
 create temp table parent (k int primary key, pd int);
 create temp table child (k int unique, cd int);
 insert into parent values (1, 10), (2, 20), (3, 30);
diff --git a/src/test/regress/sql/join.sql b/src/test/regress/sql/join.sql
index 718e1d9..c3ee72e 100644
--- a/src/test/regress/sql/join.sql
+++ b/src/test/regress/sql/join.sql
@@ -977,6 +977,89 @@ select i8.* from int8_tbl i8 left join (select f1 from int4_tbl group by f1) i4
 
 rollback;
 
+begin work;
+
+create temp table c (
+  id int primary key
+);
+create temp table b (
+  id int primary key,
+  c_id int not null,
+  val int not null,
+  constraint b_c_id_fkey foreign key (c_id) references c deferrable
+);
+create temp table a (
+  id int primary key,
+  b_id int not null,
+  constraint a_b_id_fkey foreign key (b_id) references b deferrable
+);
+
+insert into c (id) values(1);
+insert into b (id,c_id,val) values(2,1,10);
+insert into a (id,b_id) values(3,2);
+
+-- this should remove inner join to b
+explain (costs off)
+select a.* from a inner join b on a.b_id = b.id;
+
+-- this should remove inner join to b and c
+explain (costs off)
+select a.* from a inner join b on a.b_id = b.id inner join c on b.c_id = c.id;
+
+-- Ensure all of the target entries have their proper aliases.
+select a.* from a inner join b on a.b_id = b.id inner join c on b.c_id = c.id;
+
+-- change order of tables in query, this should generate the same plan as above.
+explain (costs off)
+select a.* from c inner join b on c.id = b.c_id inner join a on a.b_id = b.id;
+
+-- inner join can't be removed due to b columns in the target list
+explain (costs off)
+select * from a inner join b on a.b_id = b.id;
+
+-- this should not remove inner join to b due to quals restricting results from b
+explain (costs off)
+select a.* from a inner join b on a.b_id = b.id where b.val = 10;
+
+-- this should not remove join to b
+explain (costs off)
+select a.* from a inner join b on a.b_id = b.id where b.val = b.id;
+
+-- this should not remove the join, no foreign key exists between a.id and b.id
+explain (costs off)
+select a.* from a inner join b on a.id = b.id;
+
+-- ensure a left joined rel can't remove an inner joined rel
+explain (costs off)
+select a.* from b left join a on b.id = a.b_id;
+
+-- Ensure we remove b, but don't try and remove c. c has no join condition.
+explain (costs off)
+select a.* from a inner join b on a.b_id = b.id cross join c;
+
+set constraints b_c_id_fkey deferred;
+
+-- join should be removed.
+explain (costs off)
+select b.* from b inner join c on b.c_id = c.id;
+
+prepare ab as select b.* from b inner join c on b.c_id = c.id;
+
+explain (costs off)
+execute ab;
+
+-- perform an update which will cause some pending fk triggers to be added
+update c set id = 2 where id=1;
+
+-- ensure inner join is no longer removed.
+explain (costs off)
+select b.* from b inner join c on b.c_id = c.id;
+
+explain (costs off)
+execute ab;
+
+rollback;
+
 create temp table parent (k int primary key, pd int);
 create temp table child (k int unique, cd int);
 insert into parent values (1, 10), (2, 20), (3, 30);

diff --git a/src/backend/commands/trigger.c b/src/backend/commands/trigger.c
index e491c5b..f55acd2 100644
--- a/src/backend/commands/trigger.c
+++ b/src/backend/commands/trigger.c
@@ -3899,6 +3899,17 @@ afterTriggerInvokeEvents(AfterTriggerEventList *events,
 	return all_fired;
 }
 
+/* ----------
+ * AfterTriggerQueueIsEmpty()
+ *
+ *	True if there are no pending triggers in the queue.
+ * ----------
+ */
+bool
+AfterTriggerQueueIsEmpty(void)
+{
+	return (afterTriggers.query_depth == -1 && afterTriggers.events.head == NULL);
+}
 
 /* ----------
  * AfterTriggerBeginXact()
diff --git a/src/backend/executor/Makefile b/src/backend/executor/Makefile
index af707b0..bfbd5b3 100644
--- a/src/backend/executor/Makefile
+++ b/src/backend/executor/Makefile
@@ -14,8 +14,8 @@ include $(top_builddir)/src/Makefile.global
 
 OBJS = execAmi.o execCurrent.o execGrouping.o execJunk.o execMain.o \
        execProcnode.o execQual.o execScan.o execTuples.o \
-       execUtils.o functions.o instrument.o nodeAppend.o nodeAgg.o \
-       nodeBitmapAnd.o nodeBitmapOr.o \
+       execUtils.o functions.o instrument.o nodeAlternativePlan.o nodeAppend.o \
+       nodeAgg.o nodeBitmapAnd.o nodeBitmapOr.o \
        nodeBitmapHeapscan.o nodeBitmapIndexscan.o nodeCustom.o nodeHash.o \
        nodeHashjoin.o nodeIndexscan.o nodeIndexonlyscan.o \
        nodeLimit.o nodeLockRows.o \
diff --git a/src/backend/executor/execProcnode.c b/src/backend/executor/execProcnode.c
index 9892499..523e187 100644
--- a/src/backend/executor/execProcnode.c
+++ b/src/backend/executor/execProcnode.c
@@ -79,6 +79,7 @@
 
 #include "executor/executor.h"
 #include "executor/nodeAgg.h"
+#include "executor/nodeAlternativePlan.h"
 #include "executor/nodeAppend.h"
 #include "executor/nodeBitmapAnd.h"
 #include "executor/nodeBitmapHeapscan.h"
@@ -147,6 +148,11 @@ ExecInitNode(Plan *node, EState *estate, int eflags)
 			/*
 			 * control nodes
 			 */
+		case T_AlternativePlan:
+			result = (PlanState *) ExecInitAlternativePlan((AlternativePlan *)node,
+												  estate, eflags);
+			break;
+
 		case T_Result:
 			result = (PlanState *) ExecInitResult((Result *) node,
 												  estate, eflags);
diff --git a/src/backend/executor/nodeAlternativePlan.c b/src/backend/executor/nodeAlternativePlan.c
new file mode 100644
index 0000000..cafe33a
--- /dev/null
+++ b/src/backend/executor/nodeAlternativePlan.c
@@ -0,0 +1,51 @@
+/*-------------------------------------------------------------------------
+ *
+ * nodeAlternativePlan.c
+ *	  Node to support storage of alternative plans.
+ *
+ *	  Note that this node is rather special as it only exists while the plan
+ *	  is being initialised.
+ *
+ *	  When the initialization method is called for this node, a decision is
+ *	  made to decide which plan should be initialized, the code here then calls
+ *	  the initialize method on the selected plan and returns the state value
+ *	  from the root node of that plan.
+ *
+ * Portions Copyright (c) 1996-2015, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ *
+ * IDENTIFICATION
+ *	  src/backend/executor/nodeAlternativePlan.c
+ *
+ *-------------------------------------------------------------------------
+ */
+
+#include "postgres.h"
+
+#include "commands/trigger.h"
+
+#include "executor/executor.h"
+#include "executor/nodeAlternativePlan.h"
+
+PlanState *
+ExecInitAlternativePlan(AlternativePlan *node, EState *estate, int eflags)
+{
+	/*
+	 * If we have items in the fk trigger queue, then we'd better use the all
+	 * all purpose plan. Since an AlternativePlan node has no state, we simply
+	 * just initialize the root node of the selected plan. This means that the
+	 * AlternativePlan node is *never* seen in EXPLAIN or EXPLAIN ANALYZE.
+	 */
+	if (!AfterTriggerQueueIsEmpty())
+		return (PlanState *) ExecInitNode((Plan *) list_nth(node->planList, 1),
+											estate, eflags);
+
+	/*
+	 * Otherwise we initialize the root node of the optimized plan and return
+	 * that.
+	 */
+	else
+		return (PlanState *) ExecInitNode((Plan *) linitial(node->planList),
+											estate, eflags);
+}
diff --git a/src/backend/nodes/copyfuncs.c b/src/backend/nodes/copyfuncs.c
index 3c6a964..f23e761 100644
--- a/src/backend/nodes/copyfuncs.c
+++ b/src/backend/nodes/copyfuncs.c
@@ -94,6 +94,7 @@ _copyPlannedStmt(const PlannedStmt *from)
 	COPY_NODE_FIELD(invalItems);
 	COPY_SCALAR_FIELD(nParamExec);
 	COPY_SCALAR_FIELD(hasRowSecurity);
+	COPY_SCALAR_FIELD(suitableFor);
 
 	return newnode;
 }
@@ -965,6 +966,16 @@ _copyLimit(const Limit *from)
 	return newnode;
 }
 
+static AlternativePlan *
+_copyAlternativePlan(const AlternativePlan *from)
+{
+	AlternativePlan *newnode = makeNode(AlternativePlan);
+
+	COPY_NODE_FIELD(planList);
+
+	return newnode;
+}
+
 /*
  * _copyNestLoopParam
  */
@@ -4130,6 +4141,9 @@ copyObject(const void *from)
 		case T_Limit:
 			retval = _copyLimit(from);
 			break;
+		case T_AlternativePlan:
+			retval = _copyAlternativePlan(from);
+			break;
 		case T_NestLoopParam:
 			retval = _copyNestLoopParam(from);
 			break;
diff --git a/src/backend/nodes/outfuncs.c b/src/backend/nodes/outfuncs.c
index 385b289..440a7e2 100644
--- a/src/backend/nodes/outfuncs.c
+++ b/src/backend/nodes/outfuncs.c
@@ -256,6 +256,7 @@ _outPlannedStmt(StringInfo str, const PlannedStmt *node)
 	WRITE_NODE_FIELD(invalItems);
 	WRITE_INT_FIELD(nParamExec);
 	WRITE_BOOL_FIELD(hasRowSecurity);
+	WRITE_INT_FIELD(suitableFor);
 }
 
 /*
@@ -1723,6 +1724,7 @@ _outPlannerGlobal(StringInfo str, const PlannerGlobal *node)
 	WRITE_UINT_FIELD(lastRowMarkId);
 	WRITE_BOOL_FIELD(transientPlan);
 	WRITE_BOOL_FIELD(hasRowSecurity);
+	WRITE_INT_FIELD(suitableFor);
 }
 
 static void
@@ -1809,6 +1811,7 @@ _outRelOptInfo(StringInfo str, const RelOptInfo *node)
 	/* we don't try to print fdwroutine or fdw_private */
 	WRITE_NODE_FIELD(baserestrictinfo);
 	WRITE_NODE_FIELD(joininfo);
+	WRITE_INT_FIELD(removal_flags);
 	WRITE_BOOL_FIELD(has_eclass_joins);
 }
 
diff --git a/src/backend/optimizer/path/allpaths.c b/src/backend/optimizer/path/allpaths.c
index 58d78e6..69990a2 100644
--- a/src/backend/optimizer/path/allpaths.c
+++ b/src/backend/optimizer/path/allpaths.c
@@ -97,7 +97,8 @@ static void set_cte_pathlist(PlannerInfo *root, RelOptInfo *rel,
 				 RangeTblEntry *rte);
 static void set_worktable_pathlist(PlannerInfo *root, RelOptInfo *rel,
 					   RangeTblEntry *rte);
-static RelOptInfo *make_rel_from_joinlist(PlannerInfo *root, List *joinlist);
+static RelOptInfo *make_rel_from_joinlist(PlannerInfo *root, List *joinlist,
+					   int removal_flags);
 static bool subquery_is_pushdown_safe(Query *subquery, Query *topquery,
 						  pushdown_safety_info *safetyInfo);
 static bool recurse_pushdown_safe(Node *setOp, Query *topquery,
@@ -122,7 +123,7 @@ static void remove_unused_subquery_outputs(Query *subquery, RelOptInfo *rel);
  *	  single rel that represents the join of all base rels in the query.
  */
 RelOptInfo *
-make_one_rel(PlannerInfo *root, List *joinlist)
+make_one_rel(PlannerInfo *root, List *joinlist, int removal_flags)
 {
 	RelOptInfo *rel;
 	Index		rti;
@@ -142,7 +143,8 @@ make_one_rel(PlannerInfo *root, List *joinlist)
 		Assert(brel->relid == rti);		/* sanity check on array */
 
 		/* ignore RTEs that are "other rels" */
-		if (brel->reloptkind != RELOPT_BASEREL)
+		if (brel->reloptkind != RELOPT_BASEREL ||
+			brel->removal_flags & removal_flags)
 			continue;
 
 		root->all_baserels = bms_add_member(root->all_baserels, brel->relid);
@@ -157,12 +159,13 @@ make_one_rel(PlannerInfo *root, List *joinlist)
 	/*
 	 * Generate access paths for the entire join tree.
 	 */
-	rel = make_rel_from_joinlist(root, joinlist);
+	rel = make_rel_from_joinlist(root, joinlist, removal_flags);
+
 
 	/*
 	 * The result should join all and only the query's base rels.
 	 */
-	Assert(bms_equal(rel->relids, root->all_baserels));
+	Assert(bms_is_subset(root->all_baserels, rel->relids));
 
 	return rel;
 }
@@ -1496,7 +1499,7 @@ set_worktable_pathlist(PlannerInfo *root, RelOptInfo *rel, RangeTblEntry *rte)
  * data structure.
  */
 static RelOptInfo *
-make_rel_from_joinlist(PlannerInfo *root, List *joinlist)
+make_rel_from_joinlist(PlannerInfo *root, List *joinlist, int removal_flags)
 {
 	int			levels_needed;
 	List	   *initial_rels;
@@ -1528,11 +1531,23 @@ make_rel_from_joinlist(PlannerInfo *root, List *joinlist)
 			int			varno = ((RangeTblRef *) jlnode)->rtindex;
 
 			thisrel = find_base_rel(root, varno);
+
+			/*
+			 * If this relation can be removed for these removal_flags, then
+			 * we'll not bother including this in the list of relations to join
+			 * to
+			 */
+			if ((thisrel->removal_flags & removal_flags))
+			{
+				/* one less level needed too */
+				levels_needed--;
+				continue;
+			}
 		}
 		else if (IsA(jlnode, List))
 		{
 			/* Recurse to handle subproblem */
-			thisrel = make_rel_from_joinlist(root, (List *) jlnode);
+			thisrel = make_rel_from_joinlist(root, (List *) jlnode, removal_flags);
 		}
 		else
 		{
diff --git a/src/backend/optimizer/path/equivclass.c b/src/backend/optimizer/path/equivclass.c
index eb65c97..8ddc9db 100644
--- a/src/backend/optimizer/path/equivclass.c
+++ b/src/backend/optimizer/path/equivclass.c
@@ -49,8 +49,6 @@ static List *generate_join_implied_equalities_broken(PlannerInfo *root,
 										Relids outer_relids,
 										Relids nominal_inner_relids,
 										RelOptInfo *inner_rel);
-static Oid select_equality_operator(EquivalenceClass *ec,
-						 Oid lefttype, Oid righttype);
 static RestrictInfo *create_join_clause(PlannerInfo *root,
 				   EquivalenceClass *ec, Oid opno,
 				   EquivalenceMember *leftem,
@@ -1282,7 +1280,7 @@ generate_join_implied_equalities_broken(PlannerInfo *root,
  *
  * Returns InvalidOid if no operator can be found for this datatype combination
  */
-static Oid
+Oid
 select_equality_operator(EquivalenceClass *ec, Oid lefttype, Oid righttype)
 {
 	ListCell   *lc;
diff --git a/src/backend/optimizer/plan/analyzejoins.c b/src/backend/optimizer/plan/analyzejoins.c
index 11d3933..f52e1ee 100644
--- a/src/backend/optimizer/plan/analyzejoins.c
+++ b/src/backend/optimizer/plan/analyzejoins.c
@@ -32,13 +32,21 @@
 #include "utils/lsyscache.h"
 
 /* local functions */
-static bool join_is_removable(PlannerInfo *root, SpecialJoinInfo *sjinfo);
+static bool innerjoin_is_removable(PlannerInfo *root, List *joinlist,
+					  RangeTblRef *removalrtr, Relids ignoredrels);
+static bool leftjoin_is_removable(PlannerInfo *root, SpecialJoinInfo *sjinfo);
+static bool relation_is_needed(PlannerInfo *root, Relids joinrelids,
+					  RelOptInfo *rel, Relids ignoredrels);
+static bool relation_has_foreign_key_for(PlannerInfo *root, RelOptInfo *rel,
+					  RelOptInfo *referencedrel, List *referencing_vars,
+					  List *index_vars, List *operator_list);
+static bool expressions_match_foreign_key(ForeignKeyInfo *fk, List *fkvars,
+					  List *indexvars, List *operators);
 static void remove_rel_from_query(PlannerInfo *root, int relid,
 					  Relids joinrelids);
 static List *remove_rel_from_joinlist(List *joinlist, int relid, int *nremoved);
 static Oid	distinct_col_search(int colno, List *colnos, List *opids);
 
-
 /*
  * remove_useless_joins
  *		Check for relations that don't actually need to be joined at all,
@@ -46,26 +54,104 @@ static Oid	distinct_col_search(int colno, List *colnos, List *opids);
  *
  * We are passed the current joinlist and return the updated list.  Other
  * data structures that have to be updated are accessible via "root".
+ *
+ * There are 2 methods here for removing joins. Joins such as LEFT JOINs
+ * which can be proved to be needless due to lack of use of any of the joining
+ * relation's columns and the existence of a unique index on a subset of the
+ * join clause, can simply be removed from the query plan at plan time. For
+ * certain other join types we make use of foreign keys to attempt to prove the
+ * join is needless, though, for these we're unable to be certain that the join
+ * is not required at plan time, as if the plan is executed when pending
+ * foreign key triggers have not yet been fired, then the foreign key is
+ * effectively violated until these triggers have fired. Removing a join in
+ * such a case could cause a query to produce incorrect results.
+ *
+ * Instead we handle this case by marking the RangeTblEntry for the relation
+ * with a special flag which tells the executor that it's possible that joining
+ * to this relation may not be required. The executor may then check this flag
+ * and choose to skip the join based on if there are foreign key triggers
+ * pending or not.
  */
 List *
 remove_useless_joins(PlannerInfo *root, List *joinlist)
 {
 	ListCell   *lc;
+	Relids		removedrels = NULL;
 
 	/*
-	 * We are only interested in relations that are left-joined to, so we can
-	 * scan the join_info_list to find them easily.
+	 * Start by analyzing INNER JOINed relations in order to determine if any
+	 * of the relations can be ignored.
 	 */
 restart:
+	foreach(lc, joinlist)
+	{
+		RangeTblRef		*rtr = (RangeTblRef *) lfirst(lc);
+		RelOptInfo		*rel;
+
+		if (!IsA(rtr, RangeTblRef))
+			continue;
+
+		rel = root->simple_rel_array[rtr->rtindex];
+
+		/* Don't try to remove this one again if we've already removed it */
+		if ((rel->removal_flags & PLAN_SUITABILITY_FK_TRIGGER_EMPTY) != 0)
+			continue;
+
+		/* skip if the join can't be removed */
+		if (!innerjoin_is_removable(root, joinlist, rtr, removedrels))
+			continue;
+
+		/*
+		 * Since we're not actually removing the join here, we need to maintain
+		 * a list of relations that we've "removed" so when we're checking if
+		 * other relations can be removed we'll know that if the to be removed
+		 * relation is only referenced by a relation that we've already removed
+		 * that it can be safely assumed that the relation is not referenced by
+		 * any useful relation.
+		 */
+		removedrels = bms_add_member(removedrels, rtr->rtindex);
+
+		/*
+		 * Mark that this relation is only required when the foreign key trigger
+		 * queue us non-empty.
+		 */
+		rel->removal_flags |= PLAN_SUITABILITY_FK_TRIGGER_EMPTY;
+
+		/*
+		 * Globally mark this plan to say that there are some relations which
+		 * are only required when the foreign key trigger queue is non-empty.
+		 * The planner will later generate 2 plans, 1 which is suitable only
+		 * when all if these bitmask conditions are met, and another which is
+		 * an all purpose plan, which will be used if *any* of the bitmask's
+		 * conditions are not met.
+		 */
+		root->glob->suitableFor |= PLAN_SUITABILITY_FK_TRIGGER_EMPTY;
+
+		/*
+		 * Restart the scan.  This is necessary to ensure we find all removable
+		 * joins independently of their ordering. (note that since we've added
+		 * this relation to the removedrels, we may now realize that other
+		 * relations can also be removed as they're only referenced by the one
+		 * that we've just marked as possibly removable).
+		 */
+		goto restart;
+	}
+
+	/* now process special joins. Currently only left joins are supported */
 	foreach(lc, root->join_info_list)
 	{
 		SpecialJoinInfo *sjinfo = (SpecialJoinInfo *) lfirst(lc);
 		int			innerrelid;
 		int			nremoved;
 
-		/* Skip if not removable */
-		if (!join_is_removable(root, sjinfo))
-			continue;
+		if (sjinfo->jointype == JOIN_LEFT)
+		{
+			/* Skip if not removable */
+			if (!leftjoin_is_removable(root, sjinfo))
+				continue;
+		}
+		else
+			continue; /* we don't support this join type */
 
 		/*
 		 * Currently, join_is_removable can only succeed when the sjinfo's
@@ -91,12 +177,11 @@ restart:
 		root->join_info_list = list_delete_ptr(root->join_info_list, sjinfo);
 
 		/*
-		 * Restart the scan.  This is necessary to ensure we find all
-		 * removable joins independently of ordering of the join_info_list
-		 * (note that removal of attr_needed bits may make a join appear
-		 * removable that did not before).  Also, since we just deleted the
-		 * current list cell, we'd have to have some kluge to continue the
-		 * list scan anyway.
+		 * Restart the scan.  This is necessary to ensure we find all removable
+		 * joins independently of their ordering. (note that removal of
+		 * attr_needed bits may make a join, inner or outer, appear removable
+		 * that did not before).   Also, since we just deleted the current list
+		 * cell, we'd have to have some kluge to continue the list scan anyway.
 		 */
 		goto restart;
 	}
@@ -136,8 +221,230 @@ clause_sides_match_join(RestrictInfo *rinfo, Relids outerrelids,
 }
 
 /*
- * join_is_removable
- *	  Check whether we need not perform this special join at all, because
+ * innerjoin_is_removable
+ *		True if the join to removalrtr can be removed.
+ *
+ * In order to prove a relation which is inner joined is not required we must
+ * be sure that the join would emit exactly 1 row on the join condition. This
+ * differs from the logic which is used for proving LEFT JOINs can be removed,
+ * where it's possible to just check that a unique index exists on the relation
+ * being removed which has a set of columns that is a subset of the columns
+ * seen in the join condition. If no matching row is found then left join would
+ * not remove the non-matched row from the result set. This is not the case
+ * with INNER JOINs, so here we must use foreign keys as proof that the 1 row
+ * exists before we can allow any joins to be removed. With INNER JOINs we
+ * require that the join condition columns matches exactly to the foreign key,
+ * if there are any extra conditions then we can't ensure that the row exists,
+ * if any are missing, then we can't ensure that the relation will only produce
+ * at most 1 row for each matching on the joining relation.
+ */
+static bool
+innerjoin_is_removable(PlannerInfo *root, List *joinlist,
+					   RangeTblRef *removalrtr, Relids ignoredrels)
+{
+	ListCell   *lc;
+	RelOptInfo *removalrel;
+
+	removalrel = find_base_rel(root, removalrtr->rtindex);
+
+	/*
+	 * As foreign keys may only reference base rels which have unique indexes,
+	 * we needn't go any further if we're not dealing with a base rel, or if
+	 * the base rel has no unique indexes. We'd also better abort if the
+	 * rtekind is anything but a relation, as things like sub-queries may have
+	 * grouping or distinct clauses that would cause us not to be able to use
+	 * the foreign key to prove the existence of a row matching the join
+	 * condition. We also abort if the rel has no eclass joins as such a rel
+	 * could well be joined using some operator which is not an equality
+	 * operator, or the rel may not even be inner joined at all.
+	 *
+	 * Here we actually only check if the rel has any indexes, ideally we'd be
+	 * checking for unique indexes, but we could only determine that by looping
+	 * over the indexlist, and this is likely too expensive a check to be worth
+	 * it here.
+	 */
+	if (removalrel->reloptkind != RELOPT_BASEREL ||
+		removalrel->rtekind != RTE_RELATION ||
+		removalrel->has_eclass_joins == false ||
+		removalrel->indexlist == NIL)
+		return false;
+
+	/*
+	 * Currently we disallow the removal if we find any baserestrictinfo items
+	 * on the relation being removed. The reason for this is that these would
+	 * filter out rows and make it so the foreign key cannot prove that we'll
+	 * match exactly 1 row on the join condition. However, this check is
+	 * currently probably a bit overly strict as it should be possible to just
+	 * check and ensure that each Var seen in the baserestrictinfo is also
+	 * present in an eclass and if so, just translate and move the whole
+	 * baserestrictinfo over to the relation which has the foreign key to prove
+	 * that this join is not needed. e.g:
+	 * SELECT a.* FROM a INNER JOIN b ON a.b_id = b.id WHERE b.id = 1;
+	 * could become: SELECT a.* FROM a WHERE a.b_id = 1;
+	 */
+	if (removalrel->baserestrictinfo != NIL)
+		return false;
+
+	/*
+	 * Currently only eclass joins are supported, so if there are any non
+	 * eclass join quals then we'll report the join is non-removable.
+	 */
+	if (removalrel->joininfo != NIL)
+		return false;
+
+	/*
+	 * Now we'll search through each relation in the joinlist to see if we can
+	 * find a relation which has a foreign key which references removalrel on
+	 * the join condition. If we find a rel with a foreign key which matches
+	 * the join condition exactly, then we can be sure that exactly 1 row will
+	 * be matched on the join, if we also see that no Vars from the relation
+	 * are needed, then we can report the join as removable.
+	 */
+	foreach (lc, joinlist)
+	{
+		RangeTblRef	*rtr = (RangeTblRef *) lfirst(lc);
+		RelOptInfo	*rel;
+		ListCell	*lc2;
+		List		*referencing_vars;
+		List		*index_vars;
+		List		*operator_list;
+		Relids		 joinrelids;
+
+		/* we can't remove ourself, or anything other than RangeTblRefs */
+		if (rtr == removalrtr || !IsA(rtr, RangeTblRef))
+			continue;
+
+		rel = find_base_rel(root, rtr->rtindex);
+
+		/*
+		 * The only relation type that can help us is a base rel with at least
+		 * one foreign key defined, if there's no eclass joins then this rel
+		 * is not going to help us prove the removalrel is not needed.
+		 */
+		if (rel->reloptkind != RELOPT_BASEREL ||
+			rel->rtekind != RTE_RELATION ||
+			rel->has_eclass_joins == false ||
+			rel->fklist == NIL)
+			continue;
+
+		/*
+		 * Both rels have eclass joins, but do they have eclass joins to each
+		 * other? Skip this rel if it does not.
+		 */
+		if (!have_relevant_eclass_joinclause(root, rel, removalrel))
+			continue;
+
+		joinrelids = bms_union(rel->relids, removalrel->relids);
+
+		/* if any of the Vars from the relation are needed then abort */
+		if (relation_is_needed(root, joinrelids, removalrel, ignoredrels))
+			return false;
+
+		referencing_vars = NIL;
+		index_vars = NIL;
+		operator_list = NIL;
+
+		/* now populate the lists with the join condition Vars */
+		foreach(lc2, root->eq_classes)
+		{
+			EquivalenceClass *ec = (EquivalenceClass *) lfirst(lc2);
+
+			if (list_length(ec->ec_members) < 2 || ec->ec_has_volatile)
+				continue;
+
+			if (bms_overlap(removalrel->relids, ec->ec_relids) &&
+				bms_overlap(rel->relids, ec->ec_relids))
+			{
+				ListCell *lc3;
+				Var *refvar = NULL;
+				Var *idxvar = NULL;
+
+				/*
+				 * Look at each member of the eclass and try to find a Var from
+				 * each side of the join that we can append to the list of
+				 * columns that should be checked against each foreign key.
+				 *
+				 * The following logic does not allow for join removals to take
+				 * place for foreign keys that have duplicate columns on the
+				 * referencing side of the foreign key, such as:
+				 * (a,a) references (x,y)
+				 * The use case for such a foreign key is likely small enough
+				 * that we needn't bother making this code anymore complex to
+				 * solve. If we find more than 1 Var from any of the rels then
+				 * we'll bail out.
+				 */
+				foreach (lc3, ec->ec_members)
+				{
+					EquivalenceMember *ecm = (EquivalenceMember *) lfirst(lc3);
+
+					Var *var = (Var *) ecm->em_expr;
+
+					if (!IsA(var, Var))
+						continue; /* Skip non Vars */
+
+					if (var->varno == rel->relid)
+					{
+						if (refvar != NULL)
+							return false;
+						refvar = var;
+					}
+
+					else if (var->varno == removalrel->relid)
+					{
+						if (idxvar != NULL)
+							return false;
+						idxvar = var;
+					}
+				}
+
+				if (refvar != NULL && idxvar != NULL)
+				{
+					Oid opno;
+					Oid reloid = root->simple_rte_array[refvar->varno]->relid;
+
+					/*
+					 * We cannot allow the removal to take place if any of the
+					 * columns in the join condition are nullable. This is due
+					 * to the fact that the join condition would end up
+					 * filtering out NULL values for us, but if we remove the
+					 * join, then there's nothing to stop the NULLs getting
+					 * into the resultset.
+					 */
+					if (!get_attnotnull(reloid, refvar->varattno))
+						return false;
+
+					/* grab the correct equality operator for these two vars */
+					opno = select_equality_operator(ec, refvar->vartype, idxvar->vartype);
+
+					if (!OidIsValid(opno))
+						return false;
+
+					referencing_vars = lappend(referencing_vars, refvar);
+					index_vars = lappend(index_vars, idxvar);
+					operator_list = lappend_oid(operator_list, opno);
+				}
+			}
+		}
+
+		/*
+		 * Did we find any conditions? It's ok that we just check 1 of the 3
+		 * lists to see if it's empty here as these will always contain the
+		 * same number of items
+		 */
+		if (referencing_vars != NIL)
+		{
+			if (relation_has_foreign_key_for(root, rel, removalrel,
+				referencing_vars, index_vars, operator_list))
+				return true; /* removalrel can be removed */
+		}
+	}
+
+	return false; /* can't remove join */
+}
+
+/*
+ * leftjoin_is_removable
+ *	  Check whether we need not perform this left join at all, because
  *	  it will just duplicate its left input.
  *
  * This is true for a left join for which the join condition cannot match
@@ -147,7 +454,7 @@ clause_sides_match_join(RestrictInfo *rinfo, Relids outerrelids,
  * above the join.
  */
 static bool
-join_is_removable(PlannerInfo *root, SpecialJoinInfo *sjinfo)
+leftjoin_is_removable(PlannerInfo *root, SpecialJoinInfo *sjinfo)
 {
 	int			innerrelid;
 	RelOptInfo *innerrel;
@@ -155,14 +462,14 @@ join_is_removable(PlannerInfo *root, SpecialJoinInfo *sjinfo)
 	Relids		joinrelids;
 	List	   *clause_list = NIL;
 	ListCell   *l;
-	int			attroff;
+
+	Assert(sjinfo->jointype == JOIN_LEFT);
 
 	/*
-	 * Must be a non-delaying left join to a single baserel, else we aren't
+	 * Must be a non-delaying join to a single baserel, else we aren't
 	 * going to be able to do anything with it.
 	 */
-	if (sjinfo->jointype != JOIN_LEFT ||
-		sjinfo->delay_upper_joins)
+	if (sjinfo->delay_upper_joins)
 		return false;
 
 	if (!bms_get_singleton_member(sjinfo->min_righthand, &innerrelid))
@@ -206,52 +513,9 @@ join_is_removable(PlannerInfo *root, SpecialJoinInfo *sjinfo)
 	/* Compute the relid set for the join we are considering */
 	joinrelids = bms_union(sjinfo->min_lefthand, sjinfo->min_righthand);
 
-	/*
-	 * We can't remove the join if any inner-rel attributes are used above the
-	 * join.
-	 *
-	 * Note that this test only detects use of inner-rel attributes in higher
-	 * join conditions and the target list.  There might be such attributes in
-	 * pushed-down conditions at this join, too.  We check that case below.
-	 *
-	 * As a micro-optimization, it seems better to start with max_attr and
-	 * count down rather than starting with min_attr and counting up, on the
-	 * theory that the system attributes are somewhat less likely to be wanted
-	 * and should be tested last.
-	 */
-	for (attroff = innerrel->max_attr - innerrel->min_attr;
-		 attroff >= 0;
-		 attroff--)
-	{
-		if (!bms_is_subset(innerrel->attr_needed[attroff], joinrelids))
-			return false;
-	}
-
-	/*
-	 * Similarly check that the inner rel isn't needed by any PlaceHolderVars
-	 * that will be used above the join.  We only need to fail if such a PHV
-	 * actually references some inner-rel attributes; but the correct check
-	 * for that is relatively expensive, so we first check against ph_eval_at,
-	 * which must mention the inner rel if the PHV uses any inner-rel attrs as
-	 * non-lateral references.  Note that if the PHV's syntactic scope is just
-	 * the inner rel, we can't drop the rel even if the PHV is variable-free.
-	 */
-	foreach(l, root->placeholder_list)
-	{
-		PlaceHolderInfo *phinfo = (PlaceHolderInfo *) lfirst(l);
-
-		if (bms_is_subset(phinfo->ph_needed, joinrelids))
-			continue;			/* PHV is not used above the join */
-		if (bms_overlap(phinfo->ph_lateral, innerrel->relids))
-			return false;		/* it references innerrel laterally */
-		if (!bms_overlap(phinfo->ph_eval_at, innerrel->relids))
-			continue;			/* it definitely doesn't reference innerrel */
-		if (bms_is_subset(phinfo->ph_eval_at, innerrel->relids))
-			return false;		/* there isn't any other place to eval PHV */
-		if (bms_overlap(pull_varnos((Node *) phinfo->ph_var->phexpr),
-						innerrel->relids))
-			return false;		/* it does reference innerrel */
-	}
+	/* if the relation is referenced in the query then it cannot be removed */
+	if (relation_is_needed(root, joinrelids, innerrel, NULL))
+		return false;
 
 	/*
 	 * Search for mergejoinable clauses that constrain the inner rel against
@@ -368,6 +632,218 @@ join_is_removable(PlannerInfo *root, SpecialJoinInfo *sjinfo)
 	return false;
 }
 
+/*
+ * relation_is_needed
+ *		True if any of the Vars from this relation are required in the query
+ */
+static inline bool
+relation_is_needed(PlannerInfo *root, Relids joinrelids, RelOptInfo *rel, Relids ignoredrels)
+{
+	int		  attroff;
+	ListCell *l;
+
+	/*
+	 * rel is referenced if any of it's attributes are used above the join.
+	 *
+	 * Note that this test only detects use of rel's attributes in higher
+	 * join conditions and the target list.  There might be such attributes in
+	 * pushed-down conditions at this join, too.
+	 *
+	 * As a micro-optimization, it seems better to start with max_attr and
+	 * count down rather than starting with min_attr and counting up, on the
+	 * theory that the system attributes are somewhat less likely to be wanted
+	 * and should be tested last.
+	 */
+	for (attroff = rel->max_attr - rel->min_attr;
+		 attroff >= 0;
+		 attroff--)
+	{
+		if (!bms_is_subset(bms_difference(rel->attr_needed[attroff], ignoredrels), joinrelids))
+			return true;
+	}
+
+	/*
+	 * Similarly check that rel isn't needed by any PlaceHolderVars that will
+	 * be used above the join.  We only need to fail if such a PHV actually
+	 * references some of rel's attributes; but the correct check for that is
+	 * relatively expensive, so we first check against ph_eval_at, which must
+	 * mention rel if the PHV uses any of-rel's attrs as non-lateral
+	 * references.  Note that if the PHV's syntactic scope is just rel, we
+	 * can't return true even if the PHV is variable-free.
+	 */
+	foreach(l, root->placeholder_list)
+	{
+		PlaceHolderInfo *phinfo = (PlaceHolderInfo *) lfirst(l);
+
+		if (bms_is_subset(phinfo->ph_needed, joinrelids))
+			continue;			/* PHV is not used above the join */
+		if (bms_overlap(phinfo->ph_lateral, rel->relids))
+			return true;		/* it references rel laterally */
+		if (!bms_overlap(phinfo->ph_eval_at, rel->relids))
+			continue;			/* it definitely doesn't reference rel */
+		if (bms_is_subset(phinfo->ph_eval_at, rel->relids))
+			return true;		/* there isn't any other place to eval PHV */
+		if (bms_overlap(pull_varnos((Node *) phinfo->ph_var->phexpr),
+						rel->relids))
+			return true;		/* it does reference rel */
+	}
+
+	return false; /* it does not reference rel */
+}
+
+/*
+ * relation_has_foreign_key_for
+ *	  Checks if rel has a foreign key which references referencedrel with the
+ *	  given list of expressions.
+ *
+ *	For the match to succeed:
+ *	  referencing_vars must match the columns defined in the foreign key.
+ *	  index_vars must match the columns defined in the index for the foreign key.
+ */
+static bool
+relation_has_foreign_key_for(PlannerInfo *root, RelOptInfo *rel,
+			RelOptInfo *referencedrel, List *referencing_vars,
+			List *index_vars, List *operator_list)
+{
+	ListCell *lc;
+	Oid		  refreloid;
+
+	/*
+	 * Look up the Oid of the referenced relation. We only want to look at
+	 * foreign keys on the referencing relation which reference this relation.
+	 */
+	refreloid = root->simple_rte_array[referencedrel->relid]->relid;
+
+	Assert(list_length(referencing_vars) > 0);
+	Assert(list_length(referencing_vars) == list_length(index_vars));
+	Assert(list_length(referencing_vars) == list_length(operator_list));
+
+	/*
+	 * Search through each foreign key on the referencing relation and try
+	 * to find one which references the relation in the join condition. If we
+	 * find one then we'll send the join conditions off to
+	 * expressions_match_foreign_key() to see if they match the foreign key.
+	 */
+	foreach(lc, rel->fklist)
+	{
+		ForeignKeyInfo *fk = (ForeignKeyInfo *) lfirst(lc);
+
+		if (fk->confrelid == refreloid)
+		{
+			if (expressions_match_foreign_key(fk, referencing_vars,
+				index_vars, operator_list))
+				return true;
+		}
+	}
+
+	return false;
+}
+
+/*
+ * expressions_match_foreign_key
+ *		True if the given fkvars, indexvars and operators will match
+ *		exactly 1 record in the referenced relation of the foreign key.
+ *
+ * Note: This function expects fkvars and indexvars to only contain Var types.
+ *		 Expression indexes are not supported by foreign keys.
+ */
+static bool
+expressions_match_foreign_key(ForeignKeyInfo *fk, List *fkvars,
+					List *indexvars, List *operators)
+{
+	ListCell  *lc;
+	ListCell  *lc2;
+	ListCell  *lc3;
+	Bitmapset *allitems;
+	Bitmapset *matcheditems;
+	int		   lstidx;
+	int		   col;
+
+	Assert(list_length(fkvars) == list_length(indexvars));
+	Assert(list_length(fkvars) == list_length(operators));
+
+	/*
+	 * Fast path out if there's not enough conditions to match each column in
+	 * the foreign key. Note that we cannot check that the number of
+	 * expressions are equal here since it would cause any expressions which
+	 * are duplicated not to match.
+	 */
+	if (list_length(fkvars) < fk->conncols)
+		return false;
+
+	/*
+	 * We need to ensure that each foreign key column can be matched to a list
+	 * item, and we need to ensure that each list item can be matched to a
+	 * foreign key column. We do this by looping over each foreign key column
+	 * and checking that we can find an item in the list which matches the
+	 * current column, however this method does not allow us to ensure that no
+	 * additional items exist in the list. We could solve that by performing
+	 * another loop over each list item and check that it matches a foreign key
+	 * column, but that's a bit wasteful. Instead we'll use 2 bitmapsets, one
+	 * to store the 0 based index of each list item, and with the other we'll
+	 * store each list index that we've managed to match. After we're done
+	 * matching we'll just make sure that both bitmapsets are equal.
+	 */
+	allitems = NULL;
+	matcheditems = NULL;
+
+	/*
+	 * Build a bitmapset which contains each 1 based list index. It seems more
+	 * efficient to do this in reverse so that we allocate enough memory for
+	 * the bitmapset on first loop rather than reallocating each time we find
+	 * we need a bit more space.
+	 */
+	for (lstidx = list_length(fkvars) - 1; lstidx >= 0; lstidx--)
+		allitems = bms_add_member(allitems, lstidx);
+
+	for (col = 0; col < fk->conncols; col++)
+	{
+		bool  matched = false;
+
+		lstidx = 0;
+
+		forthree(lc, fkvars, lc2, indexvars, lc3, operators)
+		{
+			Var *expr = (Var *) lfirst(lc);
+			Var *idxexpr = (Var *) lfirst(lc2);
+			Oid  opr = lfirst_oid(lc3);
+
+			Assert(IsA(expr, Var));
+			Assert(IsA(idxexpr, Var));
+
+			/* Does this join qual match up to the current fkey column? */
+			if (fk->conkey[col] == expr->varattno &&
+				fk->confkey[col] == idxexpr->varattno &&
+				equality_ops_are_compatible(opr, fk->conpfeqop[col]))
+			{
+				matched = true;
+
+				/* mark this list item as matched */
+				matcheditems = bms_add_member(matcheditems, lstidx);
+
+				/*
+				 * Don't break here as there may be duplicate expressions
+				 * that we also need to match against.
+				 */
+			}
+			lstidx++;
+		}
+
+		/* punt if there's no match. */
+		if (!matched)
+			return false;
+	}
+
+	/*
+	 * Ensure that we managed to match every item in the list to a foreign key
+	 * column.
+	 */
+	if (!bms_equal(allitems, matcheditems))
+		return false;
+
+	return true; /* matched */
+}
+
 
 /*
  * Remove the target relid from the planner's data structures, having
diff --git a/src/backend/optimizer/plan/createplan.c b/src/backend/optimizer/plan/createplan.c
index cb69c03..6f02834 100644
--- a/src/backend/optimizer/plan/createplan.c
+++ b/src/backend/optimizer/plan/createplan.c
@@ -4679,6 +4679,15 @@ make_lockrows(Plan *lefttree, List *rowMarks, int epqParam)
 	return node;
 }
 
+AlternativePlan *
+make_alternativeplan(List *planlist)
+{
+	AlternativePlan *node = makeNode(AlternativePlan);
+	node->planList = planlist;
+
+	return node;
+}
+
 /*
  * Note: offset_est and count_est are passed in to save having to repeat
  * work already done to estimate the values of the limitOffset and limitCount
diff --git a/src/backend/optimizer/plan/planagg.c b/src/backend/optimizer/plan/planagg.c
index af772a2..22c9f30 100644
--- a/src/backend/optimizer/plan/planagg.c
+++ b/src/backend/optimizer/plan/planagg.c
@@ -409,6 +409,7 @@ build_minmax_path(PlannerInfo *root, MinMaxAggInfo *mminfo,
 	Path	   *sorted_path;
 	Cost		path_cost;
 	double		path_fraction;
+	List	   *final_rel_list;
 
 	/*----------
 	 * Generate modified query of the form
@@ -479,8 +480,12 @@ build_minmax_path(PlannerInfo *root, MinMaxAggInfo *mminfo,
 	subroot->tuple_fraction = 1.0;
 	subroot->limit_tuples = 1.0;
 
-	final_rel = query_planner(subroot, parse->targetList,
-							  minmax_qp_callback, NULL);
+	final_rel_list = query_planner(subroot, parse->targetList,
+							  minmax_qp_callback, NULL, true);
+
+	Assert(list_length(final_rel_list) ==  1);
+
+	final_rel = (RelOptInfo *) linitial(final_rel_list);
 
 	/*
 	 * Get the best presorted path, that being the one that's cheapest for
diff --git a/src/backend/optimizer/plan/planmain.c b/src/backend/optimizer/plan/planmain.c
index 848df97..b7bf67d 100644
--- a/src/backend/optimizer/plan/planmain.c
+++ b/src/backend/optimizer/plan/planmain.c
@@ -34,7 +34,7 @@
  *
  * Since query_planner does not handle the toplevel processing (grouping,
  * sorting, etc) it cannot select the best path by itself.  Instead, it
- * returns the RelOptInfo for the top level of joining, and the caller
+ * returns a list of RelOptInfo for the top level of joining, and the caller
  * (grouping_planner) can choose one of the surviving paths for the rel.
  * Normally it would choose either the rel's cheapest path, or the cheapest
  * path for the desired sort order.
@@ -50,14 +50,23 @@
  * plan.  This value is *not* available at call time, but is computed by
  * qp_callback once we have completed merging the query's equivalence classes.
  * (We cannot construct canonical pathkeys until that's done.)
+ *
+ * Note: during the planning process, the planner may discover optimization
+ * opportunities that may or may not be possible to utiliize during query
+ * execution. In this case the planner will generate 2 plans. 1 for the fully
+ * optimized version, and 1 all purpose plan which will only be used if
+ * conditions are not found to be favourable for the optimized version of the
+ * plan during executor startup.
  */
-RelOptInfo *
+List *
 query_planner(PlannerInfo *root, List *tlist,
-			  query_pathkeys_callback qp_callback, void *qp_extra)
+			  query_pathkeys_callback qp_callback, void *qp_extra,
+			  bool all_purpose_plan_only)
 {
 	Query	   *parse = root->parse;
 	List	   *joinlist;
 	RelOptInfo *final_rel;
+	List	   *final_rel_list = NIL;
 	Index		rti;
 	double		total_pages;
 
@@ -84,7 +93,7 @@ query_planner(PlannerInfo *root, List *tlist,
 		root->canon_pathkeys = NIL;
 		(*qp_callback) (root, qp_extra);
 
-		return final_rel;
+		return list_make1(final_rel);
 	}
 
 	/*
@@ -231,14 +240,37 @@ query_planner(PlannerInfo *root, List *tlist,
 	root->total_table_pages = total_pages;
 
 	/*
-	 * Ready to do the primary planning.
+	 * If the planner found any optimizations that caused the plan not to be
+	 * suitable in all situations, then we must create 2 plans. One will be
+	 * the fully the optimized version and the other will be a general purpose
+	 * plan that will only be used by the executor if any of the required
+	 * conditions for the optimization were not met. Note that we'll only
+	 * generate an optimized plan if the caller didn't specifically request an
+	 * all purpose plan.
 	 */
-	final_rel = make_one_rel(root, joinlist);
+	if (root->glob->suitableFor != PLAN_SUITABILITY_ALL_PURPOSE
+		&& all_purpose_plan_only == false)
+	{
+		/* Generate fully optimized plan, with all removable joins removed */
+		final_rel = make_one_rel(root, joinlist, root->glob->suitableFor);
+
+		/* Check that we got at least one usable path */
+		if (!final_rel || !final_rel->cheapest_total_path ||
+			final_rel->cheapest_total_path->param_info != NULL)
+			elog(ERROR, "failed to construct the join relation");
+
+		final_rel_list = lappend(final_rel_list, final_rel);
+	}
+
+	/* generate an all purpose plan */
+	final_rel = make_one_rel(root, joinlist, PLAN_SUITABILITY_ALL_PURPOSE);
 
 	/* Check that we got at least one usable path */
 	if (!final_rel || !final_rel->cheapest_total_path ||
 		final_rel->cheapest_total_path->param_info != NULL)
 		elog(ERROR, "failed to construct the join relation");
 
-	return final_rel;
+	final_rel_list = lappend(final_rel_list, final_rel);
+
+	return final_rel_list;
 }
diff --git a/src/backend/optimizer/plan/planner.c b/src/backend/optimizer/plan/planner.c
index 05687a4..8abf1da 100644
--- a/src/backend/optimizer/plan/planner.c
+++ b/src/backend/optimizer/plan/planner.c
@@ -178,6 +178,7 @@ standard_planner(Query *parse, int cursorOptions, ParamListInfo boundParams)
 	glob->lastRowMarkId = 0;
 	glob->transientPlan = false;
 	glob->hasRowSecurity = false;
+	glob->suitableFor = PLAN_SUITABILITY_ALL_PURPOSE;
 
 	/* Determine what fraction of the plan is likely to be scanned */
 	if (cursorOptions & CURSOR_OPT_FAST_PLAN)
@@ -256,6 +257,7 @@ standard_planner(Query *parse, int cursorOptions, ParamListInfo boundParams)
 	result->invalItems = glob->invalItems;
 	result->nParamExec = glob->nParamExec;
 	result->hasRowSecurity = glob->hasRowSecurity;
+	result->suitableFor = glob->suitableFor;
 
 	return result;
 }
@@ -1103,10 +1105,12 @@ grouping_planner(PlannerInfo *root, double tuple_fraction)
 	int64		count_est = 0;
 	double		limit_tuples = -1.0;
 	Plan	   *result_plan;
+	List	   *result_plan_list = NIL;
 	List	   *current_pathkeys;
 	double		dNumGroups = 0;
 	bool		use_hashed_distinct = false;
 	bool		tested_hashed_distinct = false;
+	ListCell   *lc;
 
 	/* Tweak caller-supplied tuple_fraction if have LIMIT/OFFSET */
 	if (parse->limitCount || parse->limitOffset)
@@ -1185,6 +1189,8 @@ grouping_planner(PlannerInfo *root, double tuple_fraction)
 		root->sort_pathkeys = make_pathkeys_for_sortclauses(root,
 															parse->sortClause,
 															tlist);
+
+		result_plan_list = list_make1(result_plan);
 	}
 	else
 	{
@@ -1194,6 +1200,7 @@ grouping_planner(PlannerInfo *root, double tuple_fraction)
 		bool		need_tlist_eval = true;
 		standard_qp_extra qp_extra;
 		RelOptInfo *final_rel;
+		List	   *final_rel_list;
 		Path	   *cheapest_path;
 		Path	   *sorted_path;
 		Path	   *best_path;
@@ -1304,710 +1311,723 @@ grouping_planner(PlannerInfo *root, double tuple_fraction)
 		 * standard_qp_callback) pathkey representations of the query's sort
 		 * clause, distinct clause, etc.
 		 */
-		final_rel = query_planner(root, sub_tlist,
-								  standard_qp_callback, &qp_extra);
-
-		/*
-		 * Extract rowcount and width estimates for use below.
-		 */
-		path_rows = final_rel->rows;
-		path_width = final_rel->width;
+		final_rel_list = query_planner(root, sub_tlist,
+							  standard_qp_callback, &qp_extra, false);
 
-		/*
-		 * If there's grouping going on, estimate the number of result groups.
-		 * We couldn't do this any earlier because it depends on relation size
-		 * estimates that are created within query_planner().
-		 *
-		 * Then convert tuple_fraction to fractional form if it is absolute,
-		 * and if grouping or aggregation is involved, adjust tuple_fraction
-		 * to describe the fraction of the underlying un-aggregated tuples
-		 * that will be fetched.
-		 */
-		dNumGroups = 1;			/* in case not grouping */
-
-		if (parse->groupClause)
+		foreach(lc, final_rel_list)
 		{
-			List	   *groupExprs;
-
-			groupExprs = get_sortgrouplist_exprs(parse->groupClause,
-												 parse->targetList);
-			dNumGroups = estimate_num_groups(root, groupExprs, path_rows);
-
+			final_rel = (RelOptInfo *) lfirst(lc);
 			/*
-			 * In GROUP BY mode, an absolute LIMIT is relative to the number
-			 * of groups not the number of tuples.  If the caller gave us a
-			 * fraction, keep it as-is.  (In both cases, we are effectively
-			 * assuming that all the groups are about the same size.)
+			 * Extract rowcount and width estimates for use below.
 			 */
-			if (tuple_fraction >= 1.0)
-				tuple_fraction /= dNumGroups;
+			path_rows = final_rel->rows;
+			path_width = final_rel->width;
 
 			/*
-			 * If both GROUP BY and ORDER BY are specified, we will need two
-			 * levels of sort --- and, therefore, certainly need to read all
-			 * the tuples --- unless ORDER BY is a subset of GROUP BY.
-			 * Likewise if we have both DISTINCT and GROUP BY, or if we have a
-			 * window specification not compatible with the GROUP BY.
-			 */
-			if (!pathkeys_contained_in(root->sort_pathkeys,
-									   root->group_pathkeys) ||
-				!pathkeys_contained_in(root->distinct_pathkeys,
-									   root->group_pathkeys) ||
-				!pathkeys_contained_in(root->window_pathkeys,
-									   root->group_pathkeys))
-				tuple_fraction = 0.0;
-		}
-		else if (parse->hasAggs || root->hasHavingQual)
-		{
-			/*
-			 * Ungrouped aggregate will certainly want to read all the tuples,
-			 * and it will deliver a single result row (so leave dNumGroups
-			 * set to 1).
-			 */
-			tuple_fraction = 0.0;
-		}
-		else if (parse->distinctClause)
-		{
-			/*
-			 * Since there was no grouping or aggregation, it's reasonable to
-			 * assume the UNIQUE filter has effects comparable to GROUP BY.
-			 * (If DISTINCT is used with grouping, we ignore its effects for
-			 * rowcount estimation purposes; this amounts to assuming the
-			 * grouped rows are distinct already.)
-			 */
-			List	   *distinctExprs;
-
-			distinctExprs = get_sortgrouplist_exprs(parse->distinctClause,
-													parse->targetList);
-			dNumGroups = estimate_num_groups(root, distinctExprs, path_rows);
-
-			/*
-			 * Adjust tuple_fraction the same way as for GROUP BY, too.
-			 */
-			if (tuple_fraction >= 1.0)
-				tuple_fraction /= dNumGroups;
-		}
-		else
-		{
-			/*
-			 * Plain non-grouped, non-aggregated query: an absolute tuple
-			 * fraction can be divided by the number of tuples.
+			 * If there's grouping going on, estimate the number of result groups.
+			 * We couldn't do this any earlier because it depends on relation size
+			 * estimates that are created within query_planner().
+			 *
+			 * Then convert tuple_fraction to fractional form if it is absolute,
+			 * and if grouping or aggregation is involved, adjust tuple_fraction
+			 * to describe the fraction of the underlying un-aggregated tuples
+			 * that will be fetched.
 			 */
-			if (tuple_fraction >= 1.0)
-				tuple_fraction /= path_rows;
-		}
+			dNumGroups = 1;			/* in case not grouping */
 
-		/*
-		 * Pick out the cheapest-total path as well as the cheapest presorted
-		 * path for the requested pathkeys (if there is one).  We should take
-		 * the tuple fraction into account when selecting the cheapest
-		 * presorted path, but not when selecting the cheapest-total path,
-		 * since if we have to sort then we'll have to fetch all the tuples.
-		 * (But there's a special case: if query_pathkeys is NIL, meaning
-		 * order doesn't matter, then the "cheapest presorted" path will be
-		 * the cheapest overall for the tuple fraction.)
-		 */
-		cheapest_path = final_rel->cheapest_total_path;
-
-		sorted_path =
-			get_cheapest_fractional_path_for_pathkeys(final_rel->pathlist,
-													  root->query_pathkeys,
-													  NULL,
-													  tuple_fraction);
+			if (parse->groupClause)
+			{
+				List	   *groupExprs;
 
-		/* Don't consider same path in both guises; just wastes effort */
-		if (sorted_path == cheapest_path)
-			sorted_path = NULL;
+				groupExprs = get_sortgrouplist_exprs(parse->groupClause,
+													 parse->targetList);
+				dNumGroups = estimate_num_groups(root, groupExprs, path_rows);
 
-		/*
-		 * Forget about the presorted path if it would be cheaper to sort the
-		 * cheapest-total path.  Here we need consider only the behavior at
-		 * the tuple_fraction point.  Also, limit_tuples is only relevant if
-		 * not grouping/aggregating, so use root->limit_tuples in the
-		 * cost_sort call.
-		 */
-		if (sorted_path)
-		{
-			Path		sort_path;		/* dummy for result of cost_sort */
+				/*
+				 * In GROUP BY mode, an absolute LIMIT is relative to the number
+				 * of groups not the number of tuples.  If the caller gave us a
+				 * fraction, keep it as-is.  (In both cases, we are effectively
+				 * assuming that all the groups are about the same size.)
+				 */
+				if (tuple_fraction >= 1.0)
+					tuple_fraction /= dNumGroups;
 
-			if (root->query_pathkeys == NIL ||
-				pathkeys_contained_in(root->query_pathkeys,
-									  cheapest_path->pathkeys))
-			{
-				/* No sort needed for cheapest path */
-				sort_path.startup_cost = cheapest_path->startup_cost;
-				sort_path.total_cost = cheapest_path->total_cost;
+				/*
+				 * If both GROUP BY and ORDER BY are specified, we will need two
+				 * levels of sort --- and, therefore, certainly need to read all
+				 * the tuples --- unless ORDER BY is a subset of GROUP BY.
+				 * Likewise if we have both DISTINCT and GROUP BY, or if we have a
+				 * window specification not compatible with the GROUP BY.
+				 */
+				if (!pathkeys_contained_in(root->sort_pathkeys,
+										   root->group_pathkeys) ||
+					!pathkeys_contained_in(root->distinct_pathkeys,
+										   root->group_pathkeys) ||
+					!pathkeys_contained_in(root->window_pathkeys,
+										   root->group_pathkeys))
+					tuple_fraction = 0.0;
 			}
-			else
+			else if (parse->hasAggs || root->hasHavingQual)
 			{
-				/* Figure cost for sorting */
-				cost_sort(&sort_path, root, root->query_pathkeys,
-						  cheapest_path->total_cost,
-						  path_rows, path_width,
-						  0.0, work_mem, root->limit_tuples);
+				/*
+				 * Ungrouped aggregate will certainly want to read all the tuples,
+				 * and it will deliver a single result row (so leave dNumGroups
+				 * set to 1).
+				 */
+				tuple_fraction = 0.0;
 			}
-
-			if (compare_fractional_path_costs(sorted_path, &sort_path,
-											  tuple_fraction) > 0)
+			else if (parse->distinctClause)
 			{
-				/* Presorted path is a loser */
-				sorted_path = NULL;
-			}
-		}
+				/*
+				 * Since there was no grouping or aggregation, it's reasonable to
+				 * assume the UNIQUE filter has effects comparable to GROUP BY.
+				 * (If DISTINCT is used with grouping, we ignore its effects for
+				 * rowcount estimation purposes; this amounts to assuming the
+				 * grouped rows are distinct already.)
+				 */
+				List	   *distinctExprs;
 
-		/*
-		 * Consider whether we want to use hashing instead of sorting.
-		 */
-		if (parse->groupClause)
-		{
-			/*
-			 * If grouping, decide whether to use sorted or hashed grouping.
-			 */
-			use_hashed_grouping =
-				choose_hashed_grouping(root,
-									   tuple_fraction, limit_tuples,
-									   path_rows, path_width,
-									   cheapest_path, sorted_path,
-									   dNumGroups, &agg_costs);
-			/* Also convert # groups to long int --- but 'ware overflow! */
-			numGroups = (long) Min(dNumGroups, (double) LONG_MAX);
-		}
-		else if (parse->distinctClause && sorted_path &&
-				 !root->hasHavingQual && !parse->hasAggs && !activeWindows)
-		{
-			/*
-			 * We'll reach the DISTINCT stage without any intermediate
-			 * processing, so figure out whether we will want to hash or not
-			 * so we can choose whether to use cheapest or sorted path.
-			 */
-			use_hashed_distinct =
-				choose_hashed_distinct(root,
-									   tuple_fraction, limit_tuples,
-									   path_rows, path_width,
-									   cheapest_path->startup_cost,
-									   cheapest_path->total_cost,
-									   sorted_path->startup_cost,
-									   sorted_path->total_cost,
-									   sorted_path->pathkeys,
-									   dNumGroups);
-			tested_hashed_distinct = true;
-		}
+				distinctExprs = get_sortgrouplist_exprs(parse->distinctClause,
+														parse->targetList);
+				dNumGroups = estimate_num_groups(root, distinctExprs, path_rows);
 
-		/*
-		 * Select the best path.  If we are doing hashed grouping, we will
-		 * always read all the input tuples, so use the cheapest-total path.
-		 * Otherwise, the comparison above is correct.
-		 */
-		if (use_hashed_grouping || use_hashed_distinct || !sorted_path)
-			best_path = cheapest_path;
-		else
-			best_path = sorted_path;
+				/*
+				 * Adjust tuple_fraction the same way as for GROUP BY, too.
+				 */
+				if (tuple_fraction >= 1.0)
+					tuple_fraction /= dNumGroups;
+			}
+			else
+			{
+				/*
+				 * Plain non-grouped, non-aggregated query: an absolute tuple
+				 * fraction can be divided by the number of tuples.
+				 */
+				if (tuple_fraction >= 1.0)
+					tuple_fraction /= path_rows;
+			}
 
-		/*
-		 * Check to see if it's possible to optimize MIN/MAX aggregates. If
-		 * so, we will forget all the work we did so far to choose a "regular"
-		 * path ... but we had to do it anyway to be able to tell which way is
-		 * cheaper.
-		 */
-		result_plan = optimize_minmax_aggregates(root,
-												 tlist,
-												 &agg_costs,
-												 best_path);
-		if (result_plan != NULL)
-		{
-			/*
-			 * optimize_minmax_aggregates generated the full plan, with the
-			 * right tlist, and it has no sort order.
-			 */
-			current_pathkeys = NIL;
-		}
-		else
-		{
 			/*
-			 * Normal case --- create a plan according to query_planner's
-			 * results.
+			 * Pick out the cheapest-total path as well as the cheapest presorted
+			 * path for the requested pathkeys (if there is one).  We should take
+			 * the tuple fraction into account when selecting the cheapest
+			 * presorted path, but not when selecting the cheapest-total path,
+			 * since if we have to sort then we'll have to fetch all the tuples.
+			 * (But there's a special case: if query_pathkeys is NIL, meaning
+			 * order doesn't matter, then the "cheapest presorted" path will be
+			 * the cheapest overall for the tuple fraction.)
 			 */
-			bool		need_sort_for_grouping = false;
+			cheapest_path = final_rel->cheapest_total_path;
 
-			result_plan = create_plan(root, best_path);
-			current_pathkeys = best_path->pathkeys;
+			sorted_path =
+				get_cheapest_fractional_path_for_pathkeys(final_rel->pathlist,
+														  root->query_pathkeys,
+														  NULL,
+														  tuple_fraction);
 
-			/* Detect if we'll need an explicit sort for grouping */
-			if (parse->groupClause && !use_hashed_grouping &&
-			  !pathkeys_contained_in(root->group_pathkeys, current_pathkeys))
-			{
-				need_sort_for_grouping = true;
-
-				/*
-				 * Always override create_plan's tlist, so that we don't sort
-				 * useless data from a "physical" tlist.
-				 */
-				need_tlist_eval = true;
-			}
+			/* Don't consider same path in both guises; just wastes effort */
+			if (sorted_path == cheapest_path)
+				sorted_path = NULL;
 
 			/*
-			 * create_plan returns a plan with just a "flat" tlist of required
-			 * Vars.  Usually we need to insert the sub_tlist as the tlist of
-			 * the top plan node.  However, we can skip that if we determined
-			 * that whatever create_plan chose to return will be good enough.
+			 * Forget about the presorted path if it would be cheaper to sort the
+			 * cheapest-total path.  Here we need consider only the behavior at
+			 * the tuple_fraction point.  Also, limit_tuples is only relevant if
+			 * not grouping/aggregating, so use root->limit_tuples in the
+			 * cost_sort call.
 			 */
-			if (need_tlist_eval)
+			if (sorted_path)
 			{
-				/*
-				 * If the top-level plan node is one that cannot do expression
-				 * evaluation and its existing target list isn't already what
-				 * we need, we must insert a Result node to project the
-				 * desired tlist.
-				 */
-				if (!is_projection_capable_plan(result_plan) &&
-					!tlist_same_exprs(sub_tlist, result_plan->targetlist))
+				Path		sort_path;		/* dummy for result of cost_sort */
+
+				if (root->query_pathkeys == NIL ||
+					pathkeys_contained_in(root->query_pathkeys,
+										  cheapest_path->pathkeys))
 				{
-					result_plan = (Plan *) make_result(root,
-													   sub_tlist,
-													   NULL,
-													   result_plan);
+					/* No sort needed for cheapest path */
+					sort_path.startup_cost = cheapest_path->startup_cost;
+					sort_path.total_cost = cheapest_path->total_cost;
 				}
 				else
 				{
-					/*
-					 * Otherwise, just replace the subplan's flat tlist with
-					 * the desired tlist.
-					 */
-					result_plan->targetlist = sub_tlist;
+					/* Figure cost for sorting */
+					cost_sort(&sort_path, root, root->query_pathkeys,
+							  cheapest_path->total_cost,
+							  path_rows, path_width,
+							  0.0, work_mem, root->limit_tuples);
 				}
 
+				if (compare_fractional_path_costs(sorted_path, &sort_path,
+												  tuple_fraction) > 0)
+				{
+					/* Presorted path is a loser */
+					sorted_path = NULL;
+				}
+			}
+
+			/*
+			 * Consider whether we want to use hashing instead of sorting.
+			 */
+			if (parse->groupClause)
+			{
 				/*
-				 * Also, account for the cost of evaluation of the sub_tlist.
-				 * See comments for add_tlist_costs_to_plan() for more info.
+				 * If grouping, decide whether to use sorted or hashed grouping.
 				 */
-				add_tlist_costs_to_plan(root, result_plan, sub_tlist);
+				use_hashed_grouping =
+					choose_hashed_grouping(root,
+										   tuple_fraction, limit_tuples,
+										   path_rows, path_width,
+										   cheapest_path, sorted_path,
+										   dNumGroups, &agg_costs);
+				/* Also convert # groups to long int --- but 'ware overflow! */
+				numGroups = (long) Min(dNumGroups, (double) LONG_MAX);
 			}
-			else
+			else if (parse->distinctClause && sorted_path &&
+					 !root->hasHavingQual && !parse->hasAggs && !activeWindows)
 			{
 				/*
-				 * Since we're using create_plan's tlist and not the one
-				 * make_subplanTargetList calculated, we have to refigure any
-				 * grouping-column indexes make_subplanTargetList computed.
+				 * We'll reach the DISTINCT stage without any intermediate
+				 * processing, so figure out whether we will want to hash or not
+				 * so we can choose whether to use cheapest or sorted path.
 				 */
-				locate_grouping_columns(root, tlist, result_plan->targetlist,
-										groupColIdx);
+				use_hashed_distinct =
+					choose_hashed_distinct(root,
+										   tuple_fraction, limit_tuples,
+										   path_rows, path_width,
+										   cheapest_path->startup_cost,
+										   cheapest_path->total_cost,
+										   sorted_path->startup_cost,
+										   sorted_path->total_cost,
+										   sorted_path->pathkeys,
+										   dNumGroups);
+				tested_hashed_distinct = true;
 			}
 
 			/*
-			 * Insert AGG or GROUP node if needed, plus an explicit sort step
-			 * if necessary.
-			 *
-			 * HAVING clause, if any, becomes qual of the Agg or Group node.
+			 * Select the best path.  If we are doing hashed grouping, we will
+			 * always read all the input tuples, so use the cheapest-total path.
+			 * Otherwise, the comparison above is correct.
 			 */
-			if (use_hashed_grouping)
+			if (use_hashed_grouping || use_hashed_distinct || !sorted_path)
+				best_path = cheapest_path;
+			else
+				best_path = sorted_path;
+
+			/*
+			 * Check to see if it's possible to optimize MIN/MAX aggregates. If
+			 * so, we will forget all the work we did so far to choose a "regular"
+			 * path ... but we had to do it anyway to be able to tell which way is
+			 * cheaper.
+			 */
+			result_plan = optimize_minmax_aggregates(root,
+													 tlist,
+													 &agg_costs,
+													 best_path);
+			if (result_plan != NULL)
 			{
-				/* Hashed aggregate plan --- no sort needed */
-				result_plan = (Plan *) make_agg(root,
-												tlist,
-												(List *) parse->havingQual,
-												AGG_HASHED,
-												&agg_costs,
-												numGroupCols,
-												groupColIdx,
-									extract_grouping_ops(parse->groupClause),
-												numGroups,
-												result_plan);
-				/* Hashed aggregation produces randomly-ordered results */
+				/*
+				 * optimize_minmax_aggregates generated the full plan, with the
+				 * right tlist, and it has no sort order.
+				 */
 				current_pathkeys = NIL;
 			}
-			else if (parse->hasAggs)
+			else
 			{
-				/* Plain aggregate plan --- sort if needed */
-				AggStrategy aggstrategy;
+				/*
+				 * Normal case --- create a plan according to query_planner's
+				 * results.
+				 */
+				bool		need_sort_for_grouping = false;
+
+				result_plan = create_plan(root, best_path);
+				current_pathkeys = best_path->pathkeys;
 
-				if (parse->groupClause)
+				/* Detect if we'll need an explicit sort for grouping */
+				if (parse->groupClause && !use_hashed_grouping &&
+				  !pathkeys_contained_in(root->group_pathkeys, current_pathkeys))
 				{
-					if (need_sort_for_grouping)
+					need_sort_for_grouping = true;
+
+					/*
+					 * Always override create_plan's tlist, so that we don't sort
+					 * useless data from a "physical" tlist.
+					 */
+					need_tlist_eval = true;
+				}
+
+				/*
+				 * create_plan returns a plan with just a "flat" tlist of required
+				 * Vars.  Usually we need to insert the sub_tlist as the tlist of
+				 * the top plan node.  However, we can skip that if we determined
+				 * that whatever create_plan chose to return will be good enough.
+				 */
+				if (need_tlist_eval)
+				{
+					/*
+					 * If the top-level plan node is one that cannot do expression
+					 * evaluation and its existing target list isn't already what
+					 * we need, we must insert a Result node to project the
+					 * desired tlist.
+					 */
+					if (!is_projection_capable_plan(result_plan) &&
+						!tlist_same_exprs(sub_tlist, result_plan->targetlist))
 					{
-						result_plan = (Plan *)
-							make_sort_from_groupcols(root,
-													 parse->groupClause,
-													 groupColIdx,
-													 result_plan);
-						current_pathkeys = root->group_pathkeys;
+						result_plan = (Plan *) make_result(root,
+														   sub_tlist,
+														   NULL,
+														   result_plan);
+					}
+					else
+					{
+						/*
+						 * Otherwise, just replace the subplan's flat tlist with
+						 * the desired tlist.
+						 */
+						result_plan->targetlist = sub_tlist;
 					}
-					aggstrategy = AGG_SORTED;
 
 					/*
-					 * The AGG node will not change the sort ordering of its
-					 * groups, so current_pathkeys describes the result too.
+					 * Also, account for the cost of evaluation of the sub_tlist.
+					 * See comments for add_tlist_costs_to_plan() for more info.
 					 */
+					add_tlist_costs_to_plan(root, result_plan, sub_tlist);
 				}
 				else
 				{
-					aggstrategy = AGG_PLAIN;
-					/* Result will be only one row anyway; no sort order */
-					current_pathkeys = NIL;
+					/*
+					 * Since we're using create_plan's tlist and not the one
+					 * make_subplanTargetList calculated, we have to refigure any
+					 * grouping-column indexes make_subplanTargetList computed.
+					 */
+					locate_grouping_columns(root, tlist, result_plan->targetlist,
+											groupColIdx);
 				}
 
-				result_plan = (Plan *) make_agg(root,
-												tlist,
-												(List *) parse->havingQual,
-												aggstrategy,
-												&agg_costs,
-												numGroupCols,
-												groupColIdx,
-									extract_grouping_ops(parse->groupClause),
-												numGroups,
-												result_plan);
-			}
-			else if (parse->groupClause)
-			{
 				/*
-				 * GROUP BY without aggregation, so insert a group node (plus
-				 * the appropriate sort node, if necessary).
+				 * Insert AGG or GROUP node if needed, plus an explicit sort step
+				 * if necessary.
 				 *
-				 * Add an explicit sort if we couldn't make the path come out
-				 * the way the GROUP node needs it.
+				 * HAVING clause, if any, becomes qual of the Agg or Group node.
 				 */
-				if (need_sort_for_grouping)
+				if (use_hashed_grouping)
 				{
-					result_plan = (Plan *)
-						make_sort_from_groupcols(root,
-												 parse->groupClause,
-												 groupColIdx,
-												 result_plan);
-					current_pathkeys = root->group_pathkeys;
+					/* Hashed aggregate plan --- no sort needed */
+					result_plan = (Plan *) make_agg(root,
+													tlist,
+													(List *) parse->havingQual,
+													AGG_HASHED,
+													&agg_costs,
+													numGroupCols,
+													groupColIdx,
+										extract_grouping_ops(parse->groupClause),
+													numGroups,
+													result_plan);
+					/* Hashed aggregation produces randomly-ordered results */
+					current_pathkeys = NIL;
 				}
+				else if (parse->hasAggs)
+				{
+					/* Plain aggregate plan --- sort if needed */
+					AggStrategy aggstrategy;
 
-				result_plan = (Plan *) make_group(root,
-												  tlist,
-												  (List *) parse->havingQual,
-												  numGroupCols,
-												  groupColIdx,
-									extract_grouping_ops(parse->groupClause),
-												  dNumGroups,
-												  result_plan);
-				/* The Group node won't change sort ordering */
-			}
-			else if (root->hasHavingQual)
-			{
-				/*
-				 * No aggregates, and no GROUP BY, but we have a HAVING qual.
-				 * This is a degenerate case in which we are supposed to emit
-				 * either 0 or 1 row depending on whether HAVING succeeds.
-				 * Furthermore, there cannot be any variables in either HAVING
-				 * or the targetlist, so we actually do not need the FROM
-				 * table at all!  We can just throw away the plan-so-far and
-				 * generate a Result node.  This is a sufficiently unusual
-				 * corner case that it's not worth contorting the structure of
-				 * this routine to avoid having to generate the plan in the
-				 * first place.
-				 */
-				result_plan = (Plan *) make_result(root,
-												   tlist,
-												   parse->havingQual,
-												   NULL);
-			}
-		}						/* end of non-minmax-aggregate case */
-
-		/*
-		 * Since each window function could require a different sort order, we
-		 * stack up a WindowAgg node for each window, with sort steps between
-		 * them as needed.
-		 */
-		if (activeWindows)
-		{
-			List	   *window_tlist;
-			ListCell   *l;
+					if (parse->groupClause)
+					{
+						if (need_sort_for_grouping)
+						{
+							result_plan = (Plan *)
+								make_sort_from_groupcols(root,
+														 parse->groupClause,
+														 groupColIdx,
+														 result_plan);
+							current_pathkeys = root->group_pathkeys;
+						}
+						aggstrategy = AGG_SORTED;
+
+						/*
+						 * The AGG node will not change the sort ordering of its
+						 * groups, so current_pathkeys describes the result too.
+						 */
+					}
+					else
+					{
+						aggstrategy = AGG_PLAIN;
+						/* Result will be only one row anyway; no sort order */
+						current_pathkeys = NIL;
+					}
 
-			/*
-			 * If the top-level plan node is one that cannot do expression
-			 * evaluation, we must insert a Result node to project the desired
-			 * tlist.  (In some cases this might not really be required, but
-			 * it's not worth trying to avoid it.  In particular, think not to
-			 * skip adding the Result if the initial window_tlist matches the
-			 * top-level plan node's output, because we might change the tlist
-			 * inside the following loop.)	Note that on second and subsequent
-			 * passes through the following loop, the top-level node will be a
-			 * WindowAgg which we know can project; so we only need to check
-			 * once.
-			 */
-			if (!is_projection_capable_plan(result_plan))
-			{
-				result_plan = (Plan *) make_result(root,
-												   NIL,
-												   NULL,
-												   result_plan);
-			}
+					result_plan = (Plan *) make_agg(root,
+													tlist,
+													(List *) parse->havingQual,
+													aggstrategy,
+													&agg_costs,
+													numGroupCols,
+													groupColIdx,
+										extract_grouping_ops(parse->groupClause),
+													numGroups,
+													result_plan);
+				}
+				else if (parse->groupClause)
+				{
+					/*
+					 * GROUP BY without aggregation, so insert a group node (plus
+					 * the appropriate sort node, if necessary).
+					 *
+					 * Add an explicit sort if we couldn't make the path come out
+					 * the way the GROUP node needs it.
+					 */
+					if (need_sort_for_grouping)
+					{
+						result_plan = (Plan *)
+							make_sort_from_groupcols(root,
+													 parse->groupClause,
+													 groupColIdx,
+													 result_plan);
+						current_pathkeys = root->group_pathkeys;
+					}
 
-			/*
-			 * The "base" targetlist for all steps of the windowing process is
-			 * a flat tlist of all Vars and Aggs needed in the result.  (In
-			 * some cases we wouldn't need to propagate all of these all the
-			 * way to the top, since they might only be needed as inputs to
-			 * WindowFuncs.  It's probably not worth trying to optimize that
-			 * though.)  We also add window partitioning and sorting
-			 * expressions to the base tlist, to ensure they're computed only
-			 * once at the bottom of the stack (that's critical for volatile
-			 * functions).  As we climb up the stack, we'll add outputs for
-			 * the WindowFuncs computed at each level.
-			 */
-			window_tlist = make_windowInputTargetList(root,
+					result_plan = (Plan *) make_group(root,
 													  tlist,
-													  activeWindows);
+													  (List *) parse->havingQual,
+													  numGroupCols,
+													  groupColIdx,
+										extract_grouping_ops(parse->groupClause),
+													  dNumGroups,
+													  result_plan);
+					/* The Group node won't change sort ordering */
+				}
+				else if (root->hasHavingQual)
+				{
+					/*
+					 * No aggregates, and no GROUP BY, but we have a HAVING qual.
+					 * This is a degenerate case in which we are supposed to emit
+					 * either 0 or 1 row depending on whether HAVING succeeds.
+					 * Furthermore, there cannot be any variables in either HAVING
+					 * or the targetlist, so we actually do not need the FROM
+					 * table at all!  We can just throw away the plan-so-far and
+					 * generate a Result node.  This is a sufficiently unusual
+					 * corner case that it's not worth contorting the structure of
+					 * this routine to avoid having to generate the plan in the
+					 * first place.
+					 */
+					result_plan = (Plan *) make_result(root,
+													   tlist,
+													   parse->havingQual,
+													   NULL);
+				}
+			}						/* end of non-minmax-aggregate case */
 
 			/*
-			 * The copyObject steps here are needed to ensure that each plan
-			 * node has a separately modifiable tlist.  (XXX wouldn't a
-			 * shallow list copy do for that?)
+			 * Since each window function could require a different sort order, we
+			 * stack up a WindowAgg node for each window, with sort steps between
+			 * them as needed.
 			 */
-			result_plan->targetlist = (List *) copyObject(window_tlist);
-
-			foreach(l, activeWindows)
+			if (activeWindows)
 			{
-				WindowClause *wc = (WindowClause *) lfirst(l);
-				List	   *window_pathkeys;
-				int			partNumCols;
-				AttrNumber *partColIdx;
-				Oid		   *partOperators;
-				int			ordNumCols;
-				AttrNumber *ordColIdx;
-				Oid		   *ordOperators;
-
-				window_pathkeys = make_pathkeys_for_window(root,
-														   wc,
-														   tlist);
+				List	   *window_tlist;
+				ListCell   *l;
 
 				/*
-				 * This is a bit tricky: we build a sort node even if we don't
-				 * really have to sort.  Even when no explicit sort is needed,
-				 * we need to have suitable resjunk items added to the input
-				 * plan's tlist for any partitioning or ordering columns that
-				 * aren't plain Vars.  (In theory, make_windowInputTargetList
-				 * should have provided all such columns, but let's not assume
-				 * that here.)	Furthermore, this way we can use existing
-				 * infrastructure to identify which input columns are the
-				 * interesting ones.
+				 * If the top-level plan node is one that cannot do expression
+				 * evaluation, we must insert a Result node to project the desired
+				 * tlist.  (In some cases this might not really be required, but
+				 * it's not worth trying to avoid it.  In particular, think not to
+				 * skip adding the Result if the initial window_tlist matches the
+				 * top-level plan node's output, because we might change the tlist
+				 * inside the following loop.)	Note that on second and subsequent
+				 * passes through the following loop, the top-level node will be a
+				 * WindowAgg which we know can project; so we only need to check
+				 * once.
 				 */
-				if (window_pathkeys)
-				{
-					Sort	   *sort_plan;
-
-					sort_plan = make_sort_from_pathkeys(root,
-														result_plan,
-														window_pathkeys,
-														-1.0);
-					if (!pathkeys_contained_in(window_pathkeys,
-											   current_pathkeys))
-					{
-						/* we do indeed need to sort */
-						result_plan = (Plan *) sort_plan;
-						current_pathkeys = window_pathkeys;
-					}
-					/* In either case, extract the per-column information */
-					get_column_info_for_window(root, wc, tlist,
-											   sort_plan->numCols,
-											   sort_plan->sortColIdx,
-											   &partNumCols,
-											   &partColIdx,
-											   &partOperators,
-											   &ordNumCols,
-											   &ordColIdx,
-											   &ordOperators);
-				}
-				else
+				if (!is_projection_capable_plan(result_plan))
 				{
-					/* empty window specification, nothing to sort */
-					partNumCols = 0;
-					partColIdx = NULL;
-					partOperators = NULL;
-					ordNumCols = 0;
-					ordColIdx = NULL;
-					ordOperators = NULL;
+					result_plan = (Plan *) make_result(root,
+													   NIL,
+													   NULL,
+													   result_plan);
 				}
 
-				if (lnext(l))
-				{
-					/* Add the current WindowFuncs to the running tlist */
-					window_tlist = add_to_flat_tlist(window_tlist,
-										   wflists->windowFuncs[wc->winref]);
-				}
-				else
+				/*
+				 * The "base" targetlist for all steps of the windowing process is
+				 * a flat tlist of all Vars and Aggs needed in the result.  (In
+				 * some cases we wouldn't need to propagate all of these all the
+				 * way to the top, since they might only be needed as inputs to
+				 * WindowFuncs.  It's probably not worth trying to optimize that
+				 * though.)  We also add window partitioning and sorting
+				 * expressions to the base tlist, to ensure they're computed only
+				 * once at the bottom of the stack (that's critical for volatile
+				 * functions).  As we climb up the stack, we'll add outputs for
+				 * the WindowFuncs computed at each level.
+				 */
+				window_tlist = make_windowInputTargetList(root,
+														  tlist,
+														  activeWindows);
+
+				/*
+				 * The copyObject steps here are needed to ensure that each plan
+				 * node has a separately modifiable tlist.  (XXX wouldn't a
+				 * shallow list copy do for that?)
+				 */
+				result_plan->targetlist = (List *) copyObject(window_tlist);
+
+				foreach(l, activeWindows)
 				{
-					/* Install the original tlist in the topmost WindowAgg */
-					window_tlist = tlist;
-				}
+					WindowClause *wc = (WindowClause *) lfirst(l);
+					List	   *window_pathkeys;
+					int			partNumCols;
+					AttrNumber *partColIdx;
+					Oid		   *partOperators;
+					int			ordNumCols;
+					AttrNumber *ordColIdx;
+					Oid		   *ordOperators;
+
+					window_pathkeys = make_pathkeys_for_window(root,
+															   wc,
+															   tlist);
+
+					/*
+					 * This is a bit tricky: we build a sort node even if we don't
+					 * really have to sort.  Even when no explicit sort is needed,
+					 * we need to have suitable resjunk items added to the input
+					 * plan's tlist for any partitioning or ordering columns that
+					 * aren't plain Vars.  (In theory, make_windowInputTargetList
+					 * should have provided all such columns, but let's not assume
+					 * that here.)	Furthermore, this way we can use existing
+					 * infrastructure to identify which input columns are the
+					 * interesting ones.
+					 */
+					if (window_pathkeys)
+					{
+						Sort	   *sort_plan;
+
+						sort_plan = make_sort_from_pathkeys(root,
+															result_plan,
+															window_pathkeys,
+															-1.0);
+						if (!pathkeys_contained_in(window_pathkeys,
+												   current_pathkeys))
+						{
+							/* we do indeed need to sort */
+							result_plan = (Plan *) sort_plan;
+							current_pathkeys = window_pathkeys;
+						}
+						/* In either case, extract the per-column information */
+						get_column_info_for_window(root, wc, tlist,
+												   sort_plan->numCols,
+												   sort_plan->sortColIdx,
+												   &partNumCols,
+												   &partColIdx,
+												   &partOperators,
+												   &ordNumCols,
+												   &ordColIdx,
+												   &ordOperators);
+					}
+					else
+					{
+						/* empty window specification, nothing to sort */
+						partNumCols = 0;
+						partColIdx = NULL;
+						partOperators = NULL;
+						ordNumCols = 0;
+						ordColIdx = NULL;
+						ordOperators = NULL;
+					}
 
-				/* ... and make the WindowAgg plan node */
-				result_plan = (Plan *)
-					make_windowagg(root,
-								   (List *) copyObject(window_tlist),
-								   wflists->windowFuncs[wc->winref],
-								   wc->winref,
-								   partNumCols,
-								   partColIdx,
-								   partOperators,
-								   ordNumCols,
-								   ordColIdx,
-								   ordOperators,
-								   wc->frameOptions,
-								   wc->startOffset,
-								   wc->endOffset,
-								   result_plan);
+					if (lnext(l))
+					{
+						/* Add the current WindowFuncs to the running tlist */
+						window_tlist = add_to_flat_tlist(window_tlist,
+											   wflists->windowFuncs[wc->winref]);
+					}
+					else
+					{
+						/* Install the original tlist in the topmost WindowAgg */
+						window_tlist = tlist;
+					}
+
+					/* ... and make the WindowAgg plan node */
+					result_plan = (Plan *)
+						make_windowagg(root,
+									   (List *) copyObject(window_tlist),
+									   wflists->windowFuncs[wc->winref],
+									   wc->winref,
+									   partNumCols,
+									   partColIdx,
+									   partOperators,
+									   ordNumCols,
+									   ordColIdx,
+									   ordOperators,
+									   wc->frameOptions,
+									   wc->startOffset,
+									   wc->endOffset,
+									   result_plan);
+				}
 			}
-		}
+
+			result_plan_list = lappend(result_plan_list, result_plan);
+		}						 /* foreach final_rel_list */
 	}							/* end of if (setOperations) */
 
-	/*
-	 * If there is a DISTINCT clause, add the necessary node(s).
-	 */
-	if (parse->distinctClause)
+	foreach(lc, result_plan_list)
 	{
-		double		dNumDistinctRows;
-		long		numDistinctRows;
+		result_plan = (Plan *) lfirst(lc);
 
 		/*
-		 * If there was grouping or aggregation, use the current number of
-		 * rows as the estimated number of DISTINCT rows (ie, assume the
-		 * result was already mostly unique).  If not, use the number of
-		 * distinct-groups calculated previously.
+		 * If there is a DISTINCT clause, add the necessary node(s).
 		 */
-		if (parse->groupClause || root->hasHavingQual || parse->hasAggs)
-			dNumDistinctRows = result_plan->plan_rows;
-		else
-			dNumDistinctRows = dNumGroups;
-
-		/* Also convert to long int --- but 'ware overflow! */
-		numDistinctRows = (long) Min(dNumDistinctRows, (double) LONG_MAX);
-
-		/* Choose implementation method if we didn't already */
-		if (!tested_hashed_distinct)
+		if (parse->distinctClause)
 		{
-			/*
-			 * At this point, either hashed or sorted grouping will have to
-			 * work from result_plan, so we pass that as both "cheapest" and
-			 * "sorted".
-			 */
-			use_hashed_distinct =
-				choose_hashed_distinct(root,
-									   tuple_fraction, limit_tuples,
-									   result_plan->plan_rows,
-									   result_plan->plan_width,
-									   result_plan->startup_cost,
-									   result_plan->total_cost,
-									   result_plan->startup_cost,
-									   result_plan->total_cost,
-									   current_pathkeys,
-									   dNumDistinctRows);
-		}
+			double		dNumDistinctRows;
+			long		numDistinctRows;
 
-		if (use_hashed_distinct)
-		{
-			/* Hashed aggregate plan --- no sort needed */
-			result_plan = (Plan *) make_agg(root,
-											result_plan->targetlist,
-											NIL,
-											AGG_HASHED,
-											NULL,
-										  list_length(parse->distinctClause),
-								 extract_grouping_cols(parse->distinctClause,
-													result_plan->targetlist),
-								 extract_grouping_ops(parse->distinctClause),
-											numDistinctRows,
-											result_plan);
-			/* Hashed aggregation produces randomly-ordered results */
-			current_pathkeys = NIL;
-		}
-		else
-		{
 			/*
-			 * Use a Unique node to implement DISTINCT.  Add an explicit sort
-			 * if we couldn't make the path come out the way the Unique node
-			 * needs it.  If we do have to sort, always sort by the more
-			 * rigorous of DISTINCT and ORDER BY, to avoid a second sort
-			 * below.  However, for regular DISTINCT, don't sort now if we
-			 * don't have to --- sorting afterwards will likely be cheaper,
-			 * and also has the possibility of optimizing via LIMIT.  But for
-			 * DISTINCT ON, we *must* force the final sort now, else it won't
-			 * have the desired behavior.
+			 * If there was grouping or aggregation, use the current number of
+			 * rows as the estimated number of DISTINCT rows (ie, assume the
+			 * result was already mostly unique).  If not, use the number of
+			 * distinct-groups calculated previously.
 			 */
-			List	   *needed_pathkeys;
-
-			if (parse->hasDistinctOn &&
-				list_length(root->distinct_pathkeys) <
-				list_length(root->sort_pathkeys))
-				needed_pathkeys = root->sort_pathkeys;
+			if (parse->groupClause || root->hasHavingQual || parse->hasAggs)
+				dNumDistinctRows = result_plan->plan_rows;
 			else
-				needed_pathkeys = root->distinct_pathkeys;
+				dNumDistinctRows = dNumGroups;
+
+			/* Also convert to long int --- but 'ware overflow! */
+			numDistinctRows = (long) Min(dNumDistinctRows, (double) LONG_MAX);
+
+			/* Choose implementation method if we didn't already */
+			if (!tested_hashed_distinct)
+			{
+				/*
+				 * At this point, either hashed or sorted grouping will have to
+				 * work from result_plan, so we pass that as both "cheapest" and
+				 * "sorted".
+				 */
+				use_hashed_distinct =
+					choose_hashed_distinct(root,
+										   tuple_fraction, limit_tuples,
+										   result_plan->plan_rows,
+										   result_plan->plan_width,
+										   result_plan->startup_cost,
+										   result_plan->total_cost,
+										   result_plan->startup_cost,
+										   result_plan->total_cost,
+										   current_pathkeys,
+										   dNumDistinctRows);
+			}
 
-			if (!pathkeys_contained_in(needed_pathkeys, current_pathkeys))
+			if (use_hashed_distinct)
+			{
+				/* Hashed aggregate plan --- no sort needed */
+				result_plan = (Plan *) make_agg(root,
+												result_plan->targetlist,
+												NIL,
+												AGG_HASHED,
+												NULL,
+											  list_length(parse->distinctClause),
+									 extract_grouping_cols(parse->distinctClause,
+														result_plan->targetlist),
+									 extract_grouping_ops(parse->distinctClause),
+												numDistinctRows,
+												result_plan);
+				/* Hashed aggregation produces randomly-ordered results */
+				current_pathkeys = NIL;
+			}
+			else
 			{
-				if (list_length(root->distinct_pathkeys) >=
+				/*
+				 * Use a Unique node to implement DISTINCT.  Add an explicit sort
+				 * if we couldn't make the path come out the way the Unique node
+				 * needs it.  If we do have to sort, always sort by the more
+				 * rigorous of DISTINCT and ORDER BY, to avoid a second sort
+				 * below.  However, for regular DISTINCT, don't sort now if we
+				 * don't have to --- sorting afterwards will likely be cheaper,
+				 * and also has the possibility of optimizing via LIMIT.  But for
+				 * DISTINCT ON, we *must* force the final sort now, else it won't
+				 * have the desired behavior.
+				 */
+				List	   *needed_pathkeys;
+
+				if (parse->hasDistinctOn &&
+					list_length(root->distinct_pathkeys) <
 					list_length(root->sort_pathkeys))
-					current_pathkeys = root->distinct_pathkeys;
+					needed_pathkeys = root->sort_pathkeys;
 				else
+					needed_pathkeys = root->distinct_pathkeys;
+
+				if (!pathkeys_contained_in(needed_pathkeys, current_pathkeys))
 				{
-					current_pathkeys = root->sort_pathkeys;
-					/* Assert checks that parser didn't mess up... */
-					Assert(pathkeys_contained_in(root->distinct_pathkeys,
-												 current_pathkeys));
+					if (list_length(root->distinct_pathkeys) >=
+						list_length(root->sort_pathkeys))
+						current_pathkeys = root->distinct_pathkeys;
+					else
+					{
+						current_pathkeys = root->sort_pathkeys;
+						/* Assert checks that parser didn't mess up... */
+						Assert(pathkeys_contained_in(root->distinct_pathkeys,
+													 current_pathkeys));
+					}
+
+					result_plan = (Plan *) make_sort_from_pathkeys(root,
+																   result_plan,
+																current_pathkeys,
+																   -1.0);
 				}
 
+				result_plan = (Plan *) make_unique(result_plan,
+												   parse->distinctClause);
+				result_plan->plan_rows = dNumDistinctRows;
+				/* The Unique node won't change sort ordering */
+			}
+		}
+
+		/*
+		 * If ORDER BY was given and we were not able to make the plan come out in
+		 * the right order, add an explicit sort step.
+		 */
+		if (parse->sortClause)
+		{
+			if (!pathkeys_contained_in(root->sort_pathkeys, current_pathkeys))
+			{
 				result_plan = (Plan *) make_sort_from_pathkeys(root,
 															   result_plan,
-															current_pathkeys,
-															   -1.0);
+															 root->sort_pathkeys,
+															   limit_tuples);
+				current_pathkeys = root->sort_pathkeys;
 			}
-
-			result_plan = (Plan *) make_unique(result_plan,
-											   parse->distinctClause);
-			result_plan->plan_rows = dNumDistinctRows;
-			/* The Unique node won't change sort ordering */
 		}
-	}
 
-	/*
-	 * If ORDER BY was given and we were not able to make the plan come out in
-	 * the right order, add an explicit sort step.
-	 */
-	if (parse->sortClause)
-	{
-		if (!pathkeys_contained_in(root->sort_pathkeys, current_pathkeys))
+		/*
+		 * If there is a FOR [KEY] UPDATE/SHARE clause, add the LockRows node.
+		 * (Note: we intentionally test parse->rowMarks not root->rowMarks here.
+		 * If there are only non-locking rowmarks, they should be handled by the
+		 * ModifyTable node instead.)
+		 */
+		if (parse->rowMarks)
 		{
-			result_plan = (Plan *) make_sort_from_pathkeys(root,
-														   result_plan,
-														 root->sort_pathkeys,
-														   limit_tuples);
-			current_pathkeys = root->sort_pathkeys;
-		}
-	}
+			result_plan = (Plan *) make_lockrows(result_plan,
+												 root->rowMarks,
+												 SS_assign_special_param(root));
 
-	/*
-	 * If there is a FOR [KEY] UPDATE/SHARE clause, add the LockRows node.
-	 * (Note: we intentionally test parse->rowMarks not root->rowMarks here.
-	 * If there are only non-locking rowmarks, they should be handled by the
-	 * ModifyTable node instead.)
-	 */
-	if (parse->rowMarks)
-	{
-		result_plan = (Plan *) make_lockrows(result_plan,
-											 root->rowMarks,
-											 SS_assign_special_param(root));
+			/*
+			 * The result can no longer be assumed sorted, since locking might
+			 * cause the sort key columns to be replaced with new values.
+			 */
+			current_pathkeys = NIL;
+		}
 
 		/*
-		 * The result can no longer be assumed sorted, since locking might
-		 * cause the sort key columns to be replaced with new values.
+		 * Finally, if there is a LIMIT/OFFSET clause, add the LIMIT node.
 		 */
-		current_pathkeys = NIL;
-	}
+		if (limit_needed(parse))
+		{
+			result_plan = (Plan *) make_limit(result_plan,
+											  parse->limitOffset,
+											  parse->limitCount,
+											  offset_est,
+											  count_est);
+		}
 
-	/*
-	 * Finally, if there is a LIMIT/OFFSET clause, add the LIMIT node.
-	 */
-	if (limit_needed(parse))
-	{
-		result_plan = (Plan *) make_limit(result_plan,
-										  parse->limitOffset,
-										  parse->limitCount,
-										  offset_est,
-										  count_est);
-	}
+		lfirst(lc) = result_plan;
+	} /* foreach all_plans */
 
 	/*
 	 * Return the actual output ordering in query_pathkeys for possible use by
@@ -2015,7 +2035,16 @@ grouping_planner(PlannerInfo *root, double tuple_fraction)
 	 */
 	root->query_pathkeys = current_pathkeys;
 
-	return result_plan;
+	/* if there is only one plan, then just return that plan */
+	if (list_length(result_plan_list) == 1)
+		return (Plan *) linitial(result_plan_list);
+
+	/*
+	 * Otherwise we'd better add an AlternativePlan node to allow the executor
+	 * to decide which plan to use.
+	 */
+	else
+		return (Plan *) make_alternativeplan(result_plan_list);
 }
 
 /*
diff --git a/src/backend/optimizer/plan/setrefs.c b/src/backend/optimizer/plan/setrefs.c
index ec828cd..cf7692a 100644
--- a/src/backend/optimizer/plan/setrefs.c
+++ b/src/backend/optimizer/plan/setrefs.c
@@ -434,6 +434,17 @@ set_plan_refs(PlannerInfo *root, Plan *plan, int rtoffset)
 	 */
 	switch (nodeTag(plan))
 	{
+		case T_AlternativePlan:
+			{
+				AlternativePlan *aplan = (AlternativePlan *) plan;
+				ListCell *lc;
+				foreach(lc, aplan->planList)
+				{
+					Plan *plan = (Plan *) lfirst(lc);
+					set_plan_refs(root, plan, rtoffset);
+				}
+			}
+			break;
 		case T_SeqScan:
 			{
 				SeqScan    *splan = (SeqScan *) plan;
diff --git a/src/backend/optimizer/util/plancat.c b/src/backend/optimizer/util/plancat.c
index 313a5c1..b41b965 100644
--- a/src/backend/optimizer/util/plancat.c
+++ b/src/backend/optimizer/util/plancat.c
@@ -25,7 +25,9 @@
 #include "access/transam.h"
 #include "access/xlog.h"
 #include "catalog/catalog.h"
+#include "catalog/pg_constraint.h"
 #include "catalog/heap.h"
+#include "catalog/pg_type.h"
 #include "foreign/fdwapi.h"
 #include "miscadmin.h"
 #include "nodes/makefuncs.h"
@@ -38,6 +40,7 @@
 #include "parser/parsetree.h"
 #include "rewrite/rewriteManip.h"
 #include "storage/bufmgr.h"
+#include "utils/fmgroids.h"
 #include "utils/lsyscache.h"
 #include "utils/rel.h"
 #include "utils/snapmgr.h"
@@ -89,6 +92,12 @@ get_relation_info(PlannerInfo *root, Oid relationObjectId, bool inhparent,
 	Relation	relation;
 	bool		hasindex;
 	List	   *indexinfos = NIL;
+	List	   *fkinfos = NIL;
+	Relation	fkeyRel;
+	Relation	fkeyRelIdx;
+	ScanKeyData fkeyScankey;
+	SysScanDesc fkeyScan;
+	HeapTuple	tuple;
 
 	/*
 	 * We need not lock the relation since it was already locked, either by
@@ -384,6 +393,111 @@ get_relation_info(PlannerInfo *root, Oid relationObjectId, bool inhparent,
 
 	heap_close(relation, NoLock);
 
+	/* load foreign key constraints */
+	ScanKeyInit(&fkeyScankey,
+				Anum_pg_constraint_conrelid,
+				BTEqualStrategyNumber, F_OIDEQ,
+				ObjectIdGetDatum(relationObjectId));
+
+	fkeyRel = heap_open(ConstraintRelationId, AccessShareLock);
+	fkeyRelIdx = index_open(ConstraintRelidIndexId, AccessShareLock);
+	fkeyScan = systable_beginscan_ordered(fkeyRel, fkeyRelIdx, NULL, 1, &fkeyScankey);
+
+	while ((tuple = systable_getnext_ordered(fkeyScan, ForwardScanDirection)) != NULL)
+	{
+		Form_pg_constraint con = (Form_pg_constraint) GETSTRUCT(tuple);
+		ForeignKeyInfo *fkinfo;
+		Datum		adatum;
+		bool		isNull;
+		ArrayType  *arr;
+		int			nelements;
+
+		/* skip if not a foreign key */
+		if (con->contype != CONSTRAINT_FOREIGN)
+			continue;
+
+		/* we're not interested unless the fkey has been validated */
+		if (!con->convalidated)
+			continue;
+
+		fkinfo = (ForeignKeyInfo *) palloc(sizeof(ForeignKeyInfo));
+		fkinfo->conindid = con->conindid;
+		fkinfo->confrelid = con->confrelid;
+		fkinfo->convalidated = con->convalidated;
+		fkinfo->conrelid = con->conrelid;
+		fkinfo->confupdtype = con->confupdtype;
+		fkinfo->confdeltype = con->confdeltype;
+		fkinfo->confmatchtype = con->confmatchtype;
+
+		adatum = heap_getattr(tuple, Anum_pg_constraint_conkey,
+							RelationGetDescr(fkeyRel), &isNull);
+
+		if (isNull)
+			elog(ERROR, "null conkey for constraint %u",
+				HeapTupleGetOid(tuple));
+
+		arr = DatumGetArrayTypeP(adatum);		/* ensure not toasted */
+		nelements = ARR_DIMS(arr)[0];
+		if (ARR_NDIM(arr) != 1 ||
+			nelements < 0 ||
+			ARR_HASNULL(arr) ||
+			ARR_ELEMTYPE(arr) != INT2OID)
+			elog(ERROR, "conkey is not a 1-D smallint array");
+
+		fkinfo->conkey = (int16 *) ARR_DATA_PTR(arr);
+		fkinfo->conncols = nelements;
+
+		adatum = heap_getattr(tuple, Anum_pg_constraint_confkey,
+							RelationGetDescr(fkeyRel), &isNull);
+
+		if (isNull)
+			elog(ERROR, "null confkey for constraint %u",
+				HeapTupleGetOid(tuple));
+
+		arr = DatumGetArrayTypeP(adatum);		/* ensure not toasted */
+		nelements = ARR_DIMS(arr)[0];
+
+		if (ARR_NDIM(arr) != 1 ||
+			nelements < 0 ||
+			ARR_HASNULL(arr) ||
+			ARR_ELEMTYPE(arr) != INT2OID)
+			elog(ERROR, "confkey is not a 1-D smallint array");
+
+		/* sanity check */
+		if (nelements != fkinfo->conncols)
+			elog(ERROR, "number of confkey elements does not equal conkey elements");
+
+		fkinfo->confkey = (int16 *) ARR_DATA_PTR(arr);
+		adatum = heap_getattr(tuple, Anum_pg_constraint_conpfeqop,
+							RelationGetDescr(fkeyRel), &isNull);
+
+		if (isNull)
+			elog(ERROR, "null conpfeqop for constraint %u",
+				HeapTupleGetOid(tuple));
+
+		arr = DatumGetArrayTypeP(adatum);		/* ensure not toasted */
+		nelements = ARR_DIMS(arr)[0];
+
+		if (ARR_NDIM(arr) != 1 ||
+			nelements < 0 ||
+			ARR_HASNULL(arr) ||
+			ARR_ELEMTYPE(arr) != OIDOID)
+			elog(ERROR, "conpfeqop is not a 1-D smallint array");
+
+		/* sanity check */
+		if (nelements != fkinfo->conncols)
+			elog(ERROR, "number of conpfeqop elements does not equal conkey elements");
+
+		fkinfo->conpfeqop = (Oid *) ARR_DATA_PTR(arr);
+
+		fkinfos = lappend(fkinfos, fkinfo);
+	}
+
+	rel->fklist = fkinfos;
+	systable_endscan_ordered(fkeyScan);
+	index_close(fkeyRelIdx, AccessShareLock);
+	heap_close(fkeyRel, AccessShareLock);
+
 	/*
 	 * Allow a plugin to editorialize on the info we obtained from the
 	 * catalogs.  Actions might include altering the assumed relation size,
diff --git a/src/backend/optimizer/util/relnode.c b/src/backend/optimizer/util/relnode.c
index 8cfbea0..0be29e6 100644
--- a/src/backend/optimizer/util/relnode.c
+++ b/src/backend/optimizer/util/relnode.c
@@ -115,6 +115,7 @@ build_simple_rel(PlannerInfo *root, int relid, RelOptKind reloptkind)
 	rel->lateral_relids = NULL;
 	rel->lateral_referencers = NULL;
 	rel->indexlist = NIL;
+	rel->fklist = NIL;
 	rel->pages = 0;
 	rel->tuples = 0;
 	rel->allvisfrac = 0;
@@ -127,6 +128,7 @@ build_simple_rel(PlannerInfo *root, int relid, RelOptKind reloptkind)
 	rel->baserestrictcost.startup = 0;
 	rel->baserestrictcost.per_tuple = 0;
 	rel->joininfo = NIL;
+	rel->removal_flags = PLAN_SUITABILITY_ALL_PURPOSE;
 	rel->has_eclass_joins = false;
 
 	/* Check type of rtable entry */
@@ -377,6 +379,7 @@ build_join_rel(PlannerInfo *root,
 	joinrel->lateral_relids = NULL;
 	joinrel->lateral_referencers = NULL;
 	joinrel->indexlist = NIL;
+	joinrel->fklist = NIL;
 	joinrel->pages = 0;
 	joinrel->tuples = 0;
 	joinrel->allvisfrac = 0;
@@ -389,6 +392,7 @@ build_join_rel(PlannerInfo *root,
 	joinrel->baserestrictcost.startup = 0;
 	joinrel->baserestrictcost.per_tuple = 0;
 	joinrel->joininfo = NIL;
+	joinrel->removal_flags = PLAN_SUITABILITY_ALL_PURPOSE;
 	joinrel->has_eclass_joins = false;
 
 	/*
diff --git a/src/backend/utils/cache/lsyscache.c b/src/backend/utils/cache/lsyscache.c
index 818c2f6..115e398 100644
--- a/src/backend/utils/cache/lsyscache.c
+++ b/src/backend/utils/cache/lsyscache.c
@@ -916,6 +916,33 @@ get_atttypetypmodcoll(Oid relid, AttrNumber attnum,
 	ReleaseSysCache(tp);
 }
 
+/*
+ * get_attnotnull
+ *
+ *		Given the relation id and the attribute number,
+ *		return the "attnotnull" field from the attribute relation.
+ */
+bool
+get_attnotnull(Oid relid, AttrNumber attnum)
+{
+	HeapTuple	tp;
+
+	tp = SearchSysCache2(ATTNUM,
+						 ObjectIdGetDatum(relid),
+						 Int16GetDatum(attnum));
+	if (HeapTupleIsValid(tp))
+	{
+		Form_pg_attribute att_tup = (Form_pg_attribute) GETSTRUCT(tp);
+		bool		result;
+
+		result = att_tup->attnotnull;
+		ReleaseSysCache(tp);
+		return result;
+	}
+	else
+		return false;
+}
+
 /*				---------- COLLATION CACHE ----------					 */
 
 /*
diff --git a/src/include/commands/trigger.h b/src/include/commands/trigger.h
index 1a53f6c..e02bad6 100644
--- a/src/include/commands/trigger.h
+++ b/src/include/commands/trigger.h
@@ -182,6 +182,7 @@ extern void ExecBSTruncateTriggers(EState *estate,
 extern void ExecASTruncateTriggers(EState *estate,
 					   ResultRelInfo *relinfo);
 
+extern bool AfterTriggerQueueIsEmpty(void);
 extern void AfterTriggerBeginXact(void);
 extern void AfterTriggerBeginQuery(void);
 extern void AfterTriggerEndQuery(EState *estate);
diff --git a/src/include/executor/nodeAlternativePlan.h b/src/include/executor/nodeAlternativePlan.h
new file mode 100644
index 0000000..6d830c8
--- /dev/null
+++ b/src/include/executor/nodeAlternativePlan.h
@@ -0,0 +1,25 @@
+/*-------------------------------------------------------------------------
+ *
+ * nodeAlternativePlan.h
+ *
+ *
+ *
+ * Portions Copyright (c) 1996-2015, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ * src/include/executor/nodeAlternativePlan.h
+ *
+ *-------------------------------------------------------------------------
+ */
+#ifndef NODEALTERNATIVEPLAN_H
+#define NODEALTERNATIVEPLAN_H
+
+#include "nodes/execnodes.h"
+
+extern PlanState *ExecInitAlternativePlan(AlternativePlan *node,
+						EState *estate, int eflags);
+/*
+ * Note that this node is only ever seen during initialization of a plan and
+ * it has no state type.
+ */
+#endif   /* NODEALTERNATIVEPLAN_H */
diff --git a/src/include/nodes/nodes.h b/src/include/nodes/nodes.h
index 38469ef..29f20dd 100644
--- a/src/include/nodes/nodes.h
+++ b/src/include/nodes/nodes.h
@@ -77,6 +77,7 @@ typedef enum NodeTag
 	T_SetOp,
 	T_LockRows,
 	T_Limit,
+	T_AlternativePlan,
 	/* these aren't subclasses of Plan: */
 	T_NestLoopParam,
 	T_PlanRowMark,
diff --git a/src/include/nodes/parsenodes.h b/src/include/nodes/parsenodes.h
index 50e9829..84b4e8d 100644
--- a/src/include/nodes/parsenodes.h
+++ b/src/include/nodes/parsenodes.h
@@ -752,6 +752,10 @@ typedef enum RTEKind
 	RTE_CTE						/* common table expr (WITH list element) */
 } RTEKind;
 
+/* Bit flags to mark suitability of plans */
+#define PLAN_SUITABILITY_ALL_PURPOSE		0
+#define PLAN_SUITABILITY_FK_TRIGGER_EMPTY	1
+
 typedef struct RangeTblEntry
 {
 	NodeTag		type;
diff --git a/src/include/nodes/plannodes.h b/src/include/nodes/plannodes.h
index 21cbfa8..ea7b3da 100644
--- a/src/include/nodes/plannodes.h
+++ b/src/include/nodes/plannodes.h
@@ -72,6 +72,7 @@ typedef struct PlannedStmt
 
 	bool		hasRowSecurity; /* row security applied? */
 
+	int			suitableFor; /* under which conditions can this plan be used */
 } PlannedStmt;
 
 /* macro for fetching the Plan associated with a SubPlan node */
@@ -768,6 +769,20 @@ typedef struct LockRows
 	int			epqParam;		/* ID of Param for EvalPlanQual re-eval */
 } LockRows;
 
+
+/* ----------------
+ *		alternative plan node
+ *
+ * Stores a list of alternative plans and one
+ * all purpose plan.
+ * ----------------
+ */
+typedef struct AlternativePlan
+{
+	Plan		plan;
+	List	   *planList;
+} AlternativePlan;
+
 /* ----------------
  *		limit node
  *
diff --git a/src/include/nodes/relation.h b/src/include/nodes/relation.h
index 334cf51..f0ab0ec 100644
--- a/src/include/nodes/relation.h
+++ b/src/include/nodes/relation.h
@@ -95,6 +95,8 @@ typedef struct PlannerGlobal
 
 	int			nParamExec;		/* number of PARAM_EXEC Params used */
 
+	int			suitableFor; /* under which conditions can this plan be used */
+
 	Index		lastPHId;		/* highest PlaceHolderVar ID assigned */
 
 	Index		lastRowMarkId;	/* highest PlanRowMark ID assigned */
@@ -359,6 +361,8 @@ typedef struct PlannerInfo
  *		lateral_referencers - relids of rels that reference this one laterally
  *		indexlist - list of IndexOptInfo nodes for relation's indexes
  *					(always NIL if it's not a table)
+ *		fklist - list of ForeignKeyInfo's for relation's foreign key
+ *					constraints. (always NIL if it's not a table)
  *		pages - number of disk pages in relation (zero if not a table)
  *		tuples - number of tuples in relation (not considering restrictions)
  *		allvisfrac - fraction of disk pages that are marked all-visible
@@ -452,6 +456,7 @@ typedef struct RelOptInfo
 	Relids		lateral_relids; /* minimum parameterization of rel */
 	Relids		lateral_referencers;	/* rels that reference me laterally */
 	List	   *indexlist;		/* list of IndexOptInfo */
+	List	   *fklist;			/* list of ForeignKeyInfo */
 	BlockNumber pages;			/* size estimates derived from pg_class */
 	double		tuples;
 	double		allvisfrac;
@@ -469,6 +474,8 @@ typedef struct RelOptInfo
 	QualCost	baserestrictcost;		/* cost of evaluating the above */
 	List	   *joininfo;		/* RestrictInfo structures for join clauses
 								 * involving this rel */
+	int			removal_flags;		/* it may be possible to not bother joining
+									 * this relation at all */
 	bool		has_eclass_joins;		/* T means joininfo is incomplete */
 } RelOptInfo;
 
@@ -542,6 +549,51 @@ typedef struct IndexOptInfo
 	bool		amhasgetbitmap; /* does AM have amgetbitmap interface? */
 } IndexOptInfo;
 
+/*
+ * ForeignKeyInfo
+ *		Used to store pg_constraint records for foreign key constraints for use
+ *		by the planner.
+ *
+ *		conindid - The index which supports the foreign key
+ *
+ *		confrelid - The relation that is referenced by this foreign key
+ *
+ *		convalidated - True if the foreign key has been validated.
+ *
+ *		conrelid - The Oid of the relation that the foreign key belongs to
+ *
+ *		confupdtype - ON UPDATE action for when the referenced table is updated
+ *
+ *		confdeltype - ON DELETE action, controls what to do when a record is
+ *					deleted from the referenced table.
+ *
+ *		confmatchtype - foreign key match type, e.g MATCH FULL, MATCH PARTIAL
+ *
+ *		conncols - Number of columns defined in the foreign key
+ *
+ *		conkey - An array of conncols elements to store the varattno of the
+ *					columns on the referencing side of the foreign key
+ *
+ *		confkey - An array of conncols elements to store the varattno of the
+ *					columns on the referenced side of the foreign key
+ *
+ *		conpfeqop - An array of conncols elements to store the operators for
+ *					PK = FK comparisons
+ */
+typedef struct ForeignKeyInfo
+{
+	Oid			conindid;		/* index supporting this constraint */
+	Oid			confrelid;		/* relation referenced by foreign key */
+	bool		convalidated;	/* constraint has been validated? */
+	Oid			conrelid;		/* relation this constraint constrains */
+	char		confupdtype;	/* foreign key's ON UPDATE action */
+	char		confdeltype;	/* foreign key's ON DELETE action */
+	char		confmatchtype;	/* foreign key's match type */
+	int			conncols;		/* number of columns references */
+	int16	   *conkey;			/* Columns of conrelid that the constraint applies to */
+	int16	   *confkey;		/* columns of confrelid that foreign key references */
+	Oid		   *conpfeqop;		/* Operator list for comparing PK to FK */
+} ForeignKeyInfo;
 
 /*
  * EquivalenceClasses
diff --git a/src/include/optimizer/paths.h b/src/include/optimizer/paths.h
index 6cad92e..7b040fa 100644
--- a/src/include/optimizer/paths.h
+++ b/src/include/optimizer/paths.h
@@ -37,7 +37,8 @@ typedef RelOptInfo *(*join_search_hook_type) (PlannerInfo *root,
 extern PGDLLIMPORT join_search_hook_type join_search_hook;
 
 
-extern RelOptInfo *make_one_rel(PlannerInfo *root, List *joinlist);
+extern RelOptInfo *make_one_rel(PlannerInfo *root, List *joinlist,
+								int removal_flags);
 extern RelOptInfo *standard_join_search(PlannerInfo *root, int levels_needed,
 					 List *initial_rels);
 
@@ -119,6 +120,8 @@ extern List *generate_join_implied_equalities(PlannerInfo *root,
 								 Relids join_relids,
 								 Relids outer_relids,
 								 RelOptInfo *inner_rel);
+extern Oid select_equality_operator(EquivalenceClass *ec, Oid lefttype,
+								 Oid righttype);
 extern bool exprs_known_equal(PlannerInfo *root, Node *item1, Node *item2);
 extern void add_child_rel_equivalences(PlannerInfo *root,
 						   AppendRelInfo *appinfo,
diff --git a/src/include/optimizer/planmain.h b/src/include/optimizer/planmain.h
index fa72918..d71c553 100644
--- a/src/include/optimizer/planmain.h
+++ b/src/include/optimizer/planmain.h
@@ -27,8 +27,9 @@ typedef void (*query_pathkeys_callback) (PlannerInfo *root, void *extra);
 /*
  * prototypes for plan/planmain.c
  */
-extern RelOptInfo *query_planner(PlannerInfo *root, List *tlist,
-			  query_pathkeys_callback qp_callback, void *qp_extra);
+extern List *query_planner(PlannerInfo *root, List *tlist,
+			  query_pathkeys_callback qp_callback, void *qp_extra,
+			  bool all_purpose_plan_only);
 
 /*
  * prototypes for plan/planagg.c
@@ -73,6 +74,7 @@ extern Group *make_group(PlannerInfo *root, List *tlist, List *qual,
 extern Plan *materialize_finished_plan(Plan *subplan);
 extern Unique *make_unique(Plan *lefttree, List *distinctList);
 extern LockRows *make_lockrows(Plan *lefttree, List *rowMarks, int epqParam);
+extern AlternativePlan *make_alternativeplan(List *planlist);
 extern Limit *make_limit(Plan *lefttree, Node *limitOffset, Node *limitCount,
 		   int64 offset_est, int64 count_est);
 extern SetOp *make_setop(SetOpCmd cmd, SetOpStrategy strategy, Plan *lefttree,
diff --git a/src/include/utils/lsyscache.h b/src/include/utils/lsyscache.h
index 2f5ede1..14e64fc 100644
--- a/src/include/utils/lsyscache.h
+++ b/src/include/utils/lsyscache.h
@@ -68,6 +68,7 @@ extern Oid	get_atttype(Oid relid, AttrNumber attnum);
 extern int32 get_atttypmod(Oid relid, AttrNumber attnum);
 extern void get_atttypetypmodcoll(Oid relid, AttrNumber attnum,
 					  Oid *typid, int32 *typmod, Oid *collid);
+extern bool get_attnotnull(Oid relid, AttrNumber attnum);
 extern char *get_collation_name(Oid colloid);
 extern char *get_constraint_name(Oid conoid);
 extern Oid	get_opclass_family(Oid opclass);
diff --git a/src/test/regress/expected/join.out b/src/test/regress/expected/join.out
index 57fc910..51b22b2 100644
--- a/src/test/regress/expected/join.out
+++ b/src/test/regress/expected/join.out
@@ -3301,6 +3301,171 @@ select i8.* from int8_tbl i8 left join (select f1 from int4_tbl group by f1) i4
 (1 row)
 
 rollback;
+begin work;
+create temp table c (
+  id int primary key
+);
+create temp table b (
+  id int primary key,
+  c_id int not null,
+  val int not null,
+  constraint b_c_id_fkey foreign key (c_id) references c deferrable
+);
+create temp table a (
+  id int primary key,
+  b_id int not null,
+  constraint a_b_id_fkey foreign key (b_id) references b deferrable
+);
+insert into c (id) values(1);
+insert into b (id,c_id,val) values(2,1,10);
+insert into a (id,b_id) values(3,2);
+-- this should remove inner join to b
+explain (costs off)
+select a.* from a inner join b on a.b_id = b.id;
+  QUERY PLAN   
+---------------
+ Seq Scan on a
+(1 row)
+
+-- this should remove inner join to b and c
+explain (costs off)
+select a.* from a inner join b on a.b_id = b.id inner join c on b.c_id = c.id;
+  QUERY PLAN   
+---------------
+ Seq Scan on a
+(1 row)
+
+-- Ensure all of the target entries have their proper aliases.
+select a.* from a inner join b on a.b_id = b.id inner join c on b.c_id = c.id;
+ id | b_id 
+----+------
+  3 |    2
+(1 row)
+
+-- change order of tables in query, this should generate the same plan as above.
+explain (costs off)
+select a.* from c inner join b on c.id = b.c_id inner join a on a.b_id = b.id;
+  QUERY PLAN   
+---------------
+ Seq Scan on a
+(1 row)
+
+-- inner join can't be removed due to b columns in the target list
+explain (costs off)
+select * from a inner join b on a.b_id = b.id;
+          QUERY PLAN          
+------------------------------
+ Hash Join
+   Hash Cond: (a.b_id = b.id)
+   ->  Seq Scan on a
+   ->  Hash
+         ->  Seq Scan on b
+(5 rows)
+
+-- this should not remove inner join to b due to quals restricting results from b
+explain (costs off)
+select a.* from a inner join b on a.b_id = b.id where b.val = 10;
+            QUERY PLAN            
+----------------------------------
+ Hash Join
+   Hash Cond: (a.b_id = b.id)
+   ->  Seq Scan on a
+   ->  Hash
+         ->  Seq Scan on b
+               Filter: (val = 10)
+(6 rows)
+
+-- this should not remove join to b
+explain (costs off)
+select a.* from a inner join b on a.b_id = b.id where b.val = b.id;
+            QUERY PLAN            
+----------------------------------
+ Hash Join
+   Hash Cond: (a.b_id = b.id)
+   ->  Seq Scan on a
+   ->  Hash
+         ->  Seq Scan on b
+               Filter: (id = val)
+(6 rows)
+
+-- this should not remove the join, no foreign key exists between a.id and b.id
+explain (costs off)
+select a.* from a inner join b on a.id = b.id;
+         QUERY PLAN         
+----------------------------
+ Hash Join
+   Hash Cond: (a.id = b.id)
+   ->  Seq Scan on a
+   ->  Hash
+         ->  Seq Scan on b
+(5 rows)
+
+-- ensure a left joined rel can't remove an inner joined rel
+explain (costs off)
+select a.* from b left join a on b.id = a.b_id;
+          QUERY PLAN          
+------------------------------
+ Hash Right Join
+   Hash Cond: (a.b_id = b.id)
+   ->  Seq Scan on a
+   ->  Hash
+         ->  Seq Scan on b
+(5 rows)
+
+-- Ensure we remove b, but don't try and remove c. c has no join condition.
+explain (costs off)
+select a.* from a inner join b on a.b_id = b.id cross join c;
+        QUERY PLAN         
+---------------------------
+ Nested Loop
+   ->  Seq Scan on c
+   ->  Materialize
+         ->  Seq Scan on a
+(4 rows)
+
+set constraints b_c_id_fkey deferred;
+-- join should be removed.
+explain (costs off)
+select b.* from b inner join c on b.c_id = c.id;
+  QUERY PLAN   
+---------------
+ Seq Scan on b
+(1 row)
+
+prepare ab as select b.* from b inner join c on b.c_id = c.id;
+explain (costs off)
+execute ab;
+  QUERY PLAN   
+---------------
+ Seq Scan on b
+(1 row)
+
+-- perform an update which will cause some pending fk triggers to be added
+update c set id = 2 where id=1;
+-- ensure inner join is no longer removed.
+explain (costs off)
+select b.* from b inner join c on b.c_id = c.id;
+          QUERY PLAN          
+------------------------------
+ Hash Join
+   Hash Cond: (b.c_id = c.id)
+   ->  Seq Scan on b
+   ->  Hash
+         ->  Seq Scan on c
+(5 rows)
+
+explain (costs off)
+execute ab;
+          QUERY PLAN          
+------------------------------
+ Hash Join
+   Hash Cond: (b.c_id = c.id)
+   ->  Seq Scan on b
+   ->  Hash
+         ->  Seq Scan on c
+(5 rows)
+
+rollback;
 create temp table parent (k int primary key, pd int);
 create temp table child (k int unique, cd int);
 insert into parent values (1, 10), (2, 20), (3, 30);
diff --git a/src/test/regress/sql/join.sql b/src/test/regress/sql/join.sql
index 06a27ea..e3a3314 100644
--- a/src/test/regress/sql/join.sql
+++ b/src/test/regress/sql/join.sql
@@ -990,6 +990,89 @@ select i8.* from int8_tbl i8 left join (select f1 from int4_tbl group by f1) i4
 
 rollback;
 
+begin work;
+
+create temp table c (
+  id int primary key
+);
+create temp table b (
+  id int primary key,
+  c_id int not null,
+  val int not null,
+  constraint b_c_id_fkey foreign key (c_id) references c deferrable
+);
+create temp table a (
+  id int primary key,
+  b_id int not null,
+  constraint a_b_id_fkey foreign key (b_id) references b deferrable
+);
+
+insert into c (id) values(1);
+insert into b (id,c_id,val) values(2,1,10);
+insert into a (id,b_id) values(3,2);
+
+-- this should remove inner join to b
+explain (costs off)
+select a.* from a inner join b on a.b_id = b.id;
+
+-- this should remove inner join to b and c
+explain (costs off)
+select a.* from a inner join b on a.b_id = b.id inner join c on b.c_id = c.id;
+
+-- Ensure all of the target entries have their proper aliases.
+select a.* from a inner join b on a.b_id = b.id inner join c on b.c_id = c.id;
+
+-- change order of tables in query, this should generate the same plan as above.
+explain (costs off)
+select a.* from c inner join b on c.id = b.c_id inner join a on a.b_id = b.id;
+
+-- inner join can't be removed due to b columns in the target list
+explain (costs off)
+select * from a inner join b on a.b_id = b.id;
+
+-- this should not remove inner join to b due to quals restricting results from b
+explain (costs off)
+select a.* from a inner join b on a.b_id = b.id where b.val = 10;
+
+-- this should not remove join to b
+explain (costs off)
+select a.* from a inner join b on a.b_id = b.id where b.val = b.id;
+
+-- this should not remove the join, no foreign key exists between a.id and b.id
+explain (costs off)
+select a.* from a inner join b on a.id = b.id;
+
+-- ensure a left joined rel can't remove an inner joined rel
+explain (costs off)
+select a.* from b left join a on b.id = a.b_id;
+
+-- Ensure we remove b, but don't try and remove c. c has no join condition.
+explain (costs off)
+select a.* from a inner join b on a.b_id = b.id cross join c;
+
+set constraints b_c_id_fkey deferred;
+
+-- join should be removed.
+explain (costs off)
+select b.* from b inner join c on b.c_id = c.id;
+
+prepare ab as select b.* from b inner join c on b.c_id = c.id;
+
+explain (costs off)
+execute ab;
+
+-- perform an update which will cause some pending fk triggers to be added
+update c set id = 2 where id=1;
+
+-- ensure inner join is no longer removed.
+explain (costs off)
+select b.* from b inner join c on b.c_id = c.id;
+
+explain (costs off)
+execute ab;
+
+rollback;
+
 create temp table parent (k int primary key, pd int);
 create temp table child (k int unique, cd int);
 insert into parent values (1, 10), (2, 20), (3, 30);