Refactor planner's pathkeys data structure to create a separate, explicit

representation of equivalence classes of variables.  This is an extensive
rewrite, but it brings a number of benefits:
* planner no longer fails in the presence of "incomplete" operator families
that don't offer operators for every possible combination of datatypes.
* avoid generating and then discarding redundant equality clauses.
* remove bogus assumption that derived equalities always use operators
named "=".
* mergejoins can work with a variety of sort orders (e.g., descending) now,
instead of tying each mergejoinable operator to exactly one sort order.
* better recognition of redundant sort columns.
* can make use of equalities appearing underneath an outer join.

1 files changed, 1662 insertions, 0 deletions

diff --git a/src/backend/optimizer/path/equivclass.c b/src/backend/optimizer/path/equivclass.c
new file mode 100644
index 00000000000..063e8d5d014
--- /dev/null
+++ b/src/backend/optimizer/path/equivclass.c
@@ -0,0 +1,1662 @@
+/*-------------------------------------------------------------------------
+ *
+ * equivclass.c
+ *	  Routines for managing EquivalenceClasses
+ *
+ * See src/backend/optimizer/README for discussion of EquivalenceClasses.
+ *
+ *
+ * Portions Copyright (c) 1996-2007, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ * IDENTIFICATION
+ *	  $PostgreSQL: pgsql/src/backend/optimizer/path/equivclass.c,v 1.1 2007/01/20 20:45:39 tgl Exp $
+ *
+ *-------------------------------------------------------------------------
+ */
+#include "postgres.h"
+
+#include "access/skey.h"
+#include "optimizer/clauses.h"
+#include "optimizer/cost.h"
+#include "optimizer/paths.h"
+#include "optimizer/planmain.h"
+#include "optimizer/prep.h"
+#include "optimizer/var.h"
+#include "utils/lsyscache.h"
+
+
+static void add_eq_member(EquivalenceClass *ec, Expr *expr, Relids relids,
+			  bool is_child, Oid datatype);
+static void generate_base_implied_equalities_const(PlannerInfo *root,
+												   EquivalenceClass *ec);
+static void generate_base_implied_equalities_no_const(PlannerInfo *root,
+													  EquivalenceClass *ec);
+static void generate_base_implied_equalities_broken(PlannerInfo *root,
+													EquivalenceClass *ec);
+static List *generate_join_implied_equalities_normal(PlannerInfo *root,
+										EquivalenceClass *ec,
+										RelOptInfo *joinrel,
+										RelOptInfo *outer_rel,
+										RelOptInfo *inner_rel);
+static List *generate_join_implied_equalities_broken(PlannerInfo *root,
+										EquivalenceClass *ec,
+										RelOptInfo *joinrel,
+										RelOptInfo *outer_rel,
+										RelOptInfo *inner_rel);
+static Oid	select_equality_operator(EquivalenceClass *ec,
+									 Oid lefttype, Oid righttype);
+static void reconsider_outer_join_clause(PlannerInfo *root,
+										 RestrictInfo *rinfo,
+										 bool outer_on_left);
+static void reconsider_full_join_clause(PlannerInfo *root,
+										RestrictInfo *rinfo);
+
+
+/*
+ * process_equivalence
+ *	  The given clause has a mergejoinable operator and can be applied without
+ *	  any delay by an outer join, so its two sides can be considered equal
+ *	  anywhere they are both computable; moreover that equality can be
+ *	  extended transitively.  Record this knowledge in the EquivalenceClass
+ *	  data structure.  Returns TRUE if successful, FALSE if not (in which
+ *	  case caller should treat the clause as ordinary, not an equivalence).
+ *
+ * If below_outer_join is true, then the clause was found below the nullable
+ * side of an outer join, so its sides might validly be both NULL rather than
+ * strictly equal.  We can still deduce equalities in such cases, but we take
+ * care to mark an EquivalenceClass if it came from any such clauses.  Also,
+ * we have to check that both sides are either pseudo-constants or strict
+ * functions of Vars, else they might not both go to NULL above the outer
+ * join.  (This is the reason why we need a failure return.  It's more
+ * convenient to check this case here than at the call sites...)
+ *
+ * Note: constructing merged EquivalenceClasses is a standard UNION-FIND
+ * problem, for which there exist better data structures than simple lists.
+ * If this code ever proves to be a bottleneck then it could be sped up ---
+ * but for now, simple is beautiful.
+ *
+ * Note: this is only called during planner startup, not during GEQO
+ * exploration, so we need not worry about whether we're in the right
+ * memory context.
+ */
+bool
+process_equivalence(PlannerInfo *root, RestrictInfo *restrictinfo,
+					bool below_outer_join)
+{
+	Expr	   *clause = restrictinfo->clause;
+	Oid			opno,
+				item1_type,
+				item2_type;
+	Expr	   *item1;
+	Expr	   *item2;
+	Relids		item1_relids,
+				item2_relids;
+	List	   *opfamilies;
+	EquivalenceClass *ec1,
+			   *ec2;
+	ListCell   *lc1;
+
+	/* Extract info from given clause */
+	Assert(is_opclause(clause));
+	opno = ((OpExpr *) clause)->opno;
+	item1 = (Expr *) get_leftop(clause);
+	item2 = (Expr *) get_rightop(clause);
+	item1_relids = restrictinfo->left_relids;
+	item2_relids = restrictinfo->right_relids;
+
+	/*
+	 * If below outer join, check for strictness, else reject.
+	 */
+	if (below_outer_join)
+	{
+		if (!bms_is_empty(item1_relids) &&
+			contain_nonstrict_functions((Node *) item1))
+			return false;		/* LHS is non-strict but not constant */
+		if (!bms_is_empty(item2_relids) &&
+			contain_nonstrict_functions((Node *) item2))
+			return false;		/* RHS is non-strict but not constant */
+	}
+
+	/*
+	 * We use the declared input types of the operator, not exprType() of
+	 * the inputs, as the nominal datatypes for opfamily lookup.  This
+	 * presumes that btree operators are always registered with amoplefttype
+	 * and amoprighttype equal to their declared input types.  We will need
+	 * this info anyway to build EquivalenceMember nodes, and by extracting
+	 * it now we can use type comparisons to short-circuit some equal() tests.
+	 */
+	op_input_types(opno, &item1_type, &item2_type);
+
+	opfamilies = restrictinfo->mergeopfamilies;
+
+	/*
+	 * Sweep through the existing EquivalenceClasses looking for matches
+	 * to item1 and item2.  These are the possible outcomes:
+	 *
+	 * 1. We find both in the same EC.  The equivalence is already known,
+	 * so there's nothing to do.
+	 *
+	 * 2. We find both in different ECs.  Merge the two ECs together.
+	 *
+	 * 3. We find just one.  Add the other to its EC.
+	 *
+	 * 4. We find neither.  Make a new, two-entry EC.
+	 *
+	 * Note: since all ECs are built through this process, it's impossible
+	 * that we'd match an item in more than one existing EC.  It is possible
+	 * to match more than once within an EC, if someone fed us something silly
+	 * like "WHERE X=X".  (However, we can't simply discard such clauses,
+	 * since they should fail when X is null; so we will build a 2-member
+	 * EC to ensure the correct restriction clause gets generated.  Hence
+	 * there is no shortcut here for item1 and item2 equal.)
+	 */
+	ec1 = ec2 = NULL;
+	foreach(lc1, root->eq_classes)
+	{
+		EquivalenceClass *cur_ec = (EquivalenceClass *) lfirst(lc1);
+		ListCell   *lc2;
+
+		/* Never match to a volatile EC */
+		if (cur_ec->ec_has_volatile)
+			continue;
+
+		/*
+		 * A "match" requires matching sets of btree opfamilies.  Use of
+		 * equal() for this test has implications discussed in the comments
+		 * for get_mergejoin_opfamilies().
+		 */
+		if (!equal(opfamilies, cur_ec->ec_opfamilies))
+			continue;
+
+		foreach(lc2, cur_ec->ec_members)
+		{
+			EquivalenceMember *cur_em = (EquivalenceMember *) lfirst(lc2);
+
+			Assert(!cur_em->em_is_child);				/* no children yet */
+
+			/*
+			 * If below an outer join, don't match constants: they're not
+			 * as constant as they look.
+			 */
+			if ((below_outer_join || cur_ec->ec_below_outer_join) &&
+				cur_em->em_is_const)
+				continue;
+
+			if (!ec1 &&
+				item1_type == cur_em->em_datatype &&
+				equal(item1, cur_em->em_expr))
+			{
+				ec1 = cur_ec;
+				if (ec2)
+					break;
+			}
+
+			if (!ec2 &&
+				item2_type == cur_em->em_datatype &&
+				equal(item2, cur_em->em_expr))
+			{
+				ec2 = cur_ec;
+				if (ec1)
+					break;
+			}
+		}
+
+		if (ec1 && ec2)
+			break;
+	}
+
+	/* Sweep finished, what did we find? */
+
+	if (ec1 && ec2)
+	{
+		/* If case 1, nothing to do, except add to sources */
+		if (ec1 == ec2)
+		{
+			ec1->ec_sources = lappend(ec1->ec_sources, restrictinfo);
+			ec1->ec_below_outer_join |= below_outer_join;
+			return true;
+		}
+
+		/*
+		 * Case 2: need to merge ec1 and ec2.  We add ec2's items to ec1,
+		 * then set ec2's ec_merged link to point to ec1 and remove ec2
+		 * from the eq_classes list.  We cannot simply delete ec2 because
+		 * that could leave dangling pointers in existing PathKeys.  We
+		 * leave it behind with a link so that the merged EC can be found.
+		 */
+		ec1->ec_members = list_concat(ec1->ec_members, ec2->ec_members);
+		ec1->ec_sources = list_concat(ec1->ec_sources, ec2->ec_sources);
+		ec1->ec_relids = bms_join(ec1->ec_relids, ec2->ec_relids);
+		ec1->ec_has_const |= ec2->ec_has_const;
+		/* can't need to set has_volatile */
+		ec1->ec_below_outer_join |= ec2->ec_below_outer_join;
+		ec2->ec_merged = ec1;
+		root->eq_classes = list_delete_ptr(root->eq_classes, ec2);
+		/* just to avoid debugging confusion w/ dangling pointers: */
+		ec2->ec_members = NIL;
+		ec2->ec_sources = NIL;
+		ec2->ec_relids = NULL;
+		ec1->ec_sources = lappend(ec1->ec_sources, restrictinfo);
+		ec1->ec_below_outer_join |= below_outer_join;
+	}
+	else if (ec1)
+	{
+		/* Case 3: add item2 to ec1 */
+		add_eq_member(ec1, item2, item2_relids, false, item2_type);
+		ec1->ec_sources = lappend(ec1->ec_sources, restrictinfo);
+		ec1->ec_below_outer_join |= below_outer_join;
+	}
+	else if (ec2)
+	{
+		/* Case 3: add item1 to ec2 */
+		add_eq_member(ec2, item1, item1_relids, false, item1_type);
+		ec2->ec_sources = lappend(ec2->ec_sources, restrictinfo);
+		ec2->ec_below_outer_join |= below_outer_join;
+	}
+	else
+	{
+		/* Case 4: make a new, two-entry EC */
+		EquivalenceClass *ec = makeNode(EquivalenceClass);
+
+		ec->ec_opfamilies = opfamilies;
+		ec->ec_members = NIL;
+		ec->ec_sources = list_make1(restrictinfo);
+		ec->ec_relids = NULL;
+		ec->ec_has_const = false;
+		ec->ec_has_volatile = false;
+		ec->ec_below_outer_join = below_outer_join;
+		ec->ec_broken = false;
+		ec->ec_merged = NULL;
+		add_eq_member(ec, item1, item1_relids, false, item1_type);
+		add_eq_member(ec, item2, item2_relids, false, item2_type);
+
+		root->eq_classes = lappend(root->eq_classes, ec);
+	}
+
+	return true;
+}
+
+/*
+ * add_eq_member - build a new EquivalenceMember and add it to an EC
+ */
+static void
+add_eq_member(EquivalenceClass *ec, Expr *expr, Relids relids,
+			  bool is_child, Oid datatype)
+{
+	EquivalenceMember *em = makeNode(EquivalenceMember);
+
+	em->em_expr = expr;
+	em->em_relids = relids;
+	em->em_is_const = false;
+	em->em_is_child = is_child;
+	em->em_datatype = datatype;
+
+	if (bms_is_empty(relids))
+	{
+		/*
+		 * No Vars, assume it's a pseudoconstant.  This is correct for
+		 * entries generated from process_equivalence(), because a WHERE
+		 * clause can't contain aggregates and non-volatility was checked
+		 * before process_equivalence() ever got called.  But
+		 * get_eclass_for_sort_expr() has to work harder.  We put the tests
+		 * there not here to save cycles in the equivalence case.
+		 */
+		Assert(!is_child);
+		em->em_is_const = true;
+		ec->ec_has_const = true;
+		/* it can't affect ec_relids */
+	}
+	else if (!is_child)			/* child members don't add to ec_relids */
+	{
+		ec->ec_relids = bms_add_members(ec->ec_relids, relids);
+	}
+	ec->ec_members = lappend(ec->ec_members, em);
+}
+
+
+/*
+ * get_eclass_for_sort_expr
+ *	  Given an expression and opfamily info, find an existing equivalence
+ *	  class it is a member of; if none, build a new single-member
+ *	  EquivalenceClass for it.
+ *
+ * This can be used safely both before and after EquivalenceClass merging;
+ * since it never causes merging it does not invalidate any existing ECs
+ * or PathKeys.
+ *
+ * Note: opfamilies must be chosen consistently with the way
+ * process_equivalence() would do; that is, generated from a mergejoinable
+ * equality operator.  Else we might fail to detect valid equivalences,
+ * generating poor (but not incorrect) plans.
+ */
+EquivalenceClass *
+get_eclass_for_sort_expr(PlannerInfo *root,
+						 Expr *expr,
+						 Oid expr_datatype,
+						 List *opfamilies)
+{
+	EquivalenceClass *newec;
+	ListCell   *lc1;
+	MemoryContext oldcontext;
+
+	/*
+	 * Scan through the existing EquivalenceClasses for a match
+	 */
+	foreach(lc1, root->eq_classes)
+	{
+		EquivalenceClass *cur_ec = (EquivalenceClass *) lfirst(lc1);
+		ListCell   *lc2;
+
+		/* we allow matching to a volatile EC here */
+
+		if (!equal(opfamilies, cur_ec->ec_opfamilies))
+			continue;
+
+		foreach(lc2, cur_ec->ec_members)
+		{
+			EquivalenceMember *cur_em = (EquivalenceMember *) lfirst(lc2);
+
+			/*
+			 * If below an outer join, don't match constants: they're not
+			 * as constant as they look.
+			 */
+			if (cur_ec->ec_below_outer_join &&
+				cur_em->em_is_const)
+				continue;
+
+			if (expr_datatype == cur_em->em_datatype &&
+				equal(expr, cur_em->em_expr))
+				return cur_ec;					/* Match! */
+		}
+	}
+
+	/*
+	 * No match, so build a new single-member EC
+	 *
+	 * Here, we must be sure that we construct the EC in the right context.
+	 * We can assume, however, that the passed expr is long-lived.
+	 */
+	oldcontext = MemoryContextSwitchTo(root->planner_cxt);
+
+	newec = makeNode(EquivalenceClass);
+	newec->ec_opfamilies = list_copy(opfamilies);
+	newec->ec_members = NIL;
+	newec->ec_sources = NIL;
+	newec->ec_relids = NULL;
+	newec->ec_has_const = false;
+	newec->ec_has_volatile = contain_volatile_functions((Node *) expr);
+	newec->ec_below_outer_join = false;
+	newec->ec_broken = false;
+	newec->ec_merged = NULL;
+	add_eq_member(newec, expr, pull_varnos((Node *) expr),
+				  false, expr_datatype);
+
+	/*
+	 * add_eq_member doesn't check for volatile functions or aggregates,
+	 * but such could appear in sort expressions, so we have to check
+	 * whether its const-marking was correct.
+	 */
+	if (newec->ec_has_const)
+	{
+		if (newec->ec_has_volatile || contain_agg_clause((Node *) expr))
+		{
+			newec->ec_has_const = false;
+			((EquivalenceMember *) linitial(newec->ec_members))->em_is_const = false;
+		}
+	}
+
+	root->eq_classes = lappend(root->eq_classes, newec);
+
+	MemoryContextSwitchTo(oldcontext);
+
+	return newec;
+}
+
+
+/*
+ * generate_base_implied_equalities
+ *	  Generate any restriction clauses that we can deduce from equivalence
+ *	  classes.
+ *
+ * When an EC contains pseudoconstants, our strategy is to generate
+ * "member = const1" clauses where const1 is the first constant member, for
+ * every other member (including other constants).  If we are able to do this
+ * then we don't need any "var = var" comparisons because we've successfully
+ * constrained all the vars at their points of creation.  If we fail to
+ * generate any of these clauses due to lack of cross-type operators, we fall
+ * back to the "ec_broken" strategy described below.  (XXX if there are
+ * multiple constants of different types, it's possible that we might succeed
+ * in forming all the required clauses if we started from a different const
+ * member; but this seems a sufficiently hokey corner case to not be worth
+ * spending lots of cycles on.)
+ *
+ * For ECs that contain no pseudoconstants, we generate derived clauses
+ * "member1 = member2" for each pair of members belonging to the same base
+ * relation (actually, if there are more than two for the same base relation,
+ * we only need enough clauses to link each to each other).  This provides
+ * the base case for the recursion: each row emitted by a base relation scan
+ * will constrain all computable members of the EC to be equal.  As each
+ * join path is formed, we'll add additional derived clauses on-the-fly
+ * to maintain this invariant (see generate_join_implied_equalities).
+ *
+ * If the opfamilies used by the EC do not provide complete sets of cross-type
+ * equality operators, it is possible that we will fail to generate a clause
+ * that must be generated to maintain the invariant.  (An example: given
+ * "WHERE a.x = b.y AND b.y = a.z", the scheme breaks down if we cannot
+ * generate "a.x = a.z" as a restriction clause for A.)  In this case we mark
+ * the EC "ec_broken" and fall back to regurgitating its original source
+ * RestrictInfos at appropriate times.  We do not try to retract any derived
+ * clauses already generated from the broken EC, so the resulting plan could
+ * be poor due to bad selectivity estimates caused by redundant clauses.  But
+ * the correct solution to that is to fix the opfamilies ...
+ *
+ * Equality clauses derived by this function are passed off to
+ * process_implied_equality (in plan/initsplan.c) to be inserted into the
+ * restrictinfo datastructures.  Note that this must be called after initial
+ * scanning of the quals and before Path construction begins.
+ */
+void
+generate_base_implied_equalities(PlannerInfo *root)
+{
+	ListCell   *lc;
+	Index		rti;
+
+	foreach(lc, root->eq_classes)
+	{
+		EquivalenceClass *ec = (EquivalenceClass *) lfirst(lc);
+
+		Assert(ec->ec_merged == NULL);		/* else shouldn't be in list */
+		Assert(!ec->ec_broken);				/* not yet anyway... */
+
+		/* Single-member ECs won't generate any deductions */
+		if (list_length(ec->ec_members) <= 1)
+			continue;
+
+		if (ec->ec_has_const)
+			generate_base_implied_equalities_const(root, ec);
+		else
+			generate_base_implied_equalities_no_const(root, ec);
+
+		/* Recover if we failed to generate required derived clauses */
+		if (ec->ec_broken)
+			generate_base_implied_equalities_broken(root, ec);
+	}
+
+	/*
+	 * This is also a handy place to mark base rels (which should all
+	 * exist by now) with flags showing whether they have pending eclass
+	 * joins.
+	 */
+	for (rti = 1; rti < root->simple_rel_array_size; rti++)
+	{
+		RelOptInfo *brel = root->simple_rel_array[rti];
+
+		if (brel == NULL)
+			continue;
+
+		brel->has_eclass_joins = has_relevant_eclass_joinclause(root, brel);
+	}
+}
+
+/*
+ * generate_base_implied_equalities when EC contains pseudoconstant(s)
+ */
+static void
+generate_base_implied_equalities_const(PlannerInfo *root,
+									   EquivalenceClass *ec)
+{
+	EquivalenceMember *const_em = NULL;
+	ListCell   *lc;
+
+	/* Find the constant member to use */
+	foreach(lc, ec->ec_members)
+	{
+		EquivalenceMember *cur_em = (EquivalenceMember *) lfirst(lc);
+
+		if (cur_em->em_is_const)
+		{
+			const_em = cur_em;
+			break;
+		}
+	}
+	Assert(const_em != NULL);
+
+	/* Generate a derived equality against each other member */
+	foreach(lc, ec->ec_members)
+	{
+		EquivalenceMember *cur_em = (EquivalenceMember *) lfirst(lc);
+		Oid			eq_op;
+
+		Assert(!cur_em->em_is_child);				/* no children yet */
+		if (cur_em == const_em)
+			continue;
+		eq_op = select_equality_operator(ec,
+										 cur_em->em_datatype,
+										 const_em->em_datatype);
+		if (!OidIsValid(eq_op))
+		{
+			/* failed... */
+			ec->ec_broken = true;
+			break;
+		}
+		process_implied_equality(root, eq_op,
+								 cur_em->em_expr, const_em->em_expr,
+								 ec->ec_relids,
+								 ec->ec_below_outer_join,
+								 cur_em->em_is_const);
+	}
+}
+
+/*
+ * generate_base_implied_equalities when EC contains no pseudoconstants
+ */
+static void
+generate_base_implied_equalities_no_const(PlannerInfo *root,
+										  EquivalenceClass *ec)
+{
+	EquivalenceMember **prev_ems;
+	ListCell   *lc;
+
+	/*
+	 * We scan the EC members once and track the last-seen member for each
+	 * base relation.  When we see another member of the same base relation,
+	 * we generate "prev_mem = cur_mem".  This results in the minimum number
+	 * of derived clauses, but it's possible that it will fail when a different
+	 * ordering would succeed.  XXX FIXME: use a UNION-FIND algorithm similar
+	 * to the way we build merged ECs.  (Use a list-of-lists for each rel.)
+	 */
+	prev_ems = (EquivalenceMember **)
+		palloc0(root->simple_rel_array_size * sizeof(EquivalenceMember *));
+
+	foreach(lc, ec->ec_members)
+	{
+		EquivalenceMember *cur_em = (EquivalenceMember *) lfirst(lc);
+		int			relid;
+
+		Assert(!cur_em->em_is_child);				/* no children yet */
+		if (bms_membership(cur_em->em_relids) != BMS_SINGLETON)
+			continue;
+		relid = bms_singleton_member(cur_em->em_relids);
+		Assert(relid < root->simple_rel_array_size);
+
+		if (prev_ems[relid] != NULL)
+		{
+			EquivalenceMember *prev_em = prev_ems[relid];
+			Oid			eq_op;
+
+			eq_op = select_equality_operator(ec,
+											 prev_em->em_datatype,
+											 cur_em->em_datatype);
+			if (!OidIsValid(eq_op))
+			{
+				/* failed... */
+				ec->ec_broken = true;
+				break;
+			}
+			process_implied_equality(root, eq_op,
+									 prev_em->em_expr, cur_em->em_expr,
+									 ec->ec_relids,
+									 ec->ec_below_outer_join,
+									 false);
+		}
+		prev_ems[relid] = cur_em;
+	}
+
+	pfree(prev_ems);
+
+	/*
+	 * We also have to make sure that all the Vars used in the member
+	 * clauses will be available at any join node we might try to reference
+	 * them at.  For the moment we force all the Vars to be available at
+	 * all join nodes for this eclass.  Perhaps this could be improved by
+	 * doing some pre-analysis of which members we prefer to join, but it's
+	 * no worse than what happened in the pre-8.3 code.
+	 */
+	foreach(lc, ec->ec_members)
+	{
+		EquivalenceMember *cur_em = (EquivalenceMember *) lfirst(lc);
+		List	   *vars = pull_var_clause((Node *) cur_em->em_expr, false);
+
+		add_vars_to_targetlist(root, vars, ec->ec_relids);
+		list_free(vars);
+	}
+}
+
+/*
+ * generate_base_implied_equalities cleanup after failure
+ *
+ * What we must do here is push any zero- or one-relation source RestrictInfos
+ * of the EC back into the main restrictinfo datastructures.  Multi-relation
+ * clauses will be regurgitated later by generate_join_implied_equalities().
+ * (We do it this way to maintain continuity with the case that ec_broken
+ * becomes set only after we've gone up a join level or two.)
+ */
+static void
+generate_base_implied_equalities_broken(PlannerInfo *root,
+										EquivalenceClass *ec)
+{
+	ListCell   *lc;
+
+	foreach(lc, ec->ec_sources)
+	{
+		RestrictInfo *restrictinfo = (RestrictInfo *) lfirst(lc);
+
+		if (bms_membership(restrictinfo->required_relids) != BMS_MULTIPLE)
+			distribute_restrictinfo_to_rels(root, restrictinfo);
+	}
+}
+
+
+/*
+ * generate_join_implied_equalities
+ *	  Generate any join clauses that we can deduce from equivalence classes.
+ *
+ * At a join node, we must enforce restriction clauses sufficient to ensure
+ * that all equivalence-class members computable at that node are equal.
+ * Since the set of clauses to enforce can vary depending on which subset
+ * relations are the inputs, we have to compute this afresh for each join
+ * path pair.  Hence a fresh List of RestrictInfo nodes is built and passed
+ * back on each call.
+ *
+ * The results are sufficient for use in merge, hash, and plain nestloop join
+ * methods.  We do not worry here about selecting clauses that are optimal
+ * for use in a nestloop-with-inner-indexscan join, however.  indxpath.c makes
+ * its own selections of clauses to use, and if the ones we pick here are
+ * redundant with those, the extras will be eliminated in createplan.c.
+ */
+List *
+generate_join_implied_equalities(PlannerInfo *root,
+								 RelOptInfo *joinrel,
+								 RelOptInfo *outer_rel,
+								 RelOptInfo *inner_rel)
+{
+	List	   *result = NIL;
+	ListCell   *lc;
+
+	foreach(lc, root->eq_classes)
+	{
+		EquivalenceClass *ec = (EquivalenceClass *) lfirst(lc);
+		List   *sublist = NIL;
+
+		/* ECs containing consts do not need any further enforcement */
+		if (ec->ec_has_const)
+			continue;
+
+		/* Single-member ECs won't generate any deductions */
+		if (list_length(ec->ec_members) <= 1)
+			continue;
+
+		/* We can quickly ignore any that don't overlap the join, too */
+		if (!bms_overlap(ec->ec_relids, joinrel->relids))
+			continue;
+
+		if (!ec->ec_broken)
+			sublist = generate_join_implied_equalities_normal(root,
+															  ec,
+															  joinrel,
+															  outer_rel,
+															  inner_rel);
+
+		/* Recover if we failed to generate required derived clauses */
+		if (ec->ec_broken)
+			sublist = generate_join_implied_equalities_broken(root,
+															  ec,
+															  joinrel,
+															  outer_rel,
+															  inner_rel);
+
+		result = list_concat(result, sublist);
+	}
+
+	return result;
+}
+
+/*
+ * generate_join_implied_equalities for a still-valid EC
+ */
+static List *
+generate_join_implied_equalities_normal(PlannerInfo *root,
+										EquivalenceClass *ec,
+										RelOptInfo *joinrel,
+										RelOptInfo *outer_rel,
+										RelOptInfo *inner_rel)
+{
+	List	   *result = NIL;
+	List	   *new_members = NIL;
+	List	   *outer_members = NIL;
+	List	   *inner_members = NIL;
+	ListCell   *lc1;
+
+	/*
+	 * First, scan the EC to identify member values that are computable
+	 * at the outer rel, at the inner rel, or at this relation but not in
+	 * either input rel.  The outer-rel members should already be enforced
+	 * equal, likewise for the inner-rel members.  We'll need to create
+	 * clauses to enforce that any newly computable members are all equal
+	 * to each other as well as to at least one input member, plus enforce
+	 * at least one outer-rel member equal to at least one inner-rel member.
+	 */
+	foreach(lc1, ec->ec_members)
+	{
+		EquivalenceMember *cur_em = (EquivalenceMember *) lfirst(lc1);
+
+		if (cur_em->em_is_child)
+			continue;			/* ignore children here */
+		if (!bms_is_subset(cur_em->em_relids, joinrel->relids))
+			continue;			/* ignore --- not computable yet */
+
+		if (bms_is_subset(cur_em->em_relids, outer_rel->relids))
+			outer_members = lappend(outer_members, cur_em);
+		else if (bms_is_subset(cur_em->em_relids, inner_rel->relids))
+			inner_members = lappend(inner_members, cur_em);
+		else
+			new_members = lappend(new_members, cur_em);
+	}
+
+	/*
+	 * First, select the joinclause if needed.  We can equate any one outer
+	 * member to any one inner member, but we have to find a datatype
+	 * combination for which an opfamily member operator exists.  If we
+	 * have choices, we prefer simple Var members (possibly with RelabelType)
+	 * since these are (a) cheapest to compute at runtime and (b) most likely
+	 * to have useful statistics.  Also, if enable_hashjoin is on, we prefer
+	 * operators that are also hashjoinable.
+	 */
+	if (outer_members && inner_members)
+	{
+		EquivalenceMember *best_outer_em = NULL;
+		EquivalenceMember *best_inner_em = NULL;
+		Oid		best_eq_op = InvalidOid;
+		int		best_score = -1;
+		RestrictInfo *rinfo;
+
+		foreach(lc1, outer_members)
+		{
+			EquivalenceMember *outer_em = (EquivalenceMember *) lfirst(lc1);
+			ListCell   *lc2;
+
+			foreach(lc2, inner_members)
+			{
+				EquivalenceMember *inner_em = (EquivalenceMember *) lfirst(lc2);
+				Oid		eq_op;
+				int		score;
+
+				eq_op = select_equality_operator(ec,
+												 outer_em->em_datatype,
+												 inner_em->em_datatype);
+				if (!OidIsValid(eq_op))
+					continue;
+				score = 0;
+				if (IsA(outer_em->em_expr, Var) ||
+					(IsA(outer_em->em_expr, RelabelType) &&
+					 IsA(((RelabelType *) outer_em->em_expr)->arg, Var)))
+					score++;
+				if (IsA(inner_em->em_expr, Var) ||
+					(IsA(inner_em->em_expr, RelabelType) &&
+					 IsA(((RelabelType *) inner_em->em_expr)->arg, Var)))
+					score++;
+				if (!enable_hashjoin || op_hashjoinable(eq_op))
+					score++;
+				if (score > best_score)
+				{
+					best_outer_em = outer_em;
+					best_inner_em = inner_em;
+					best_eq_op = eq_op;
+					best_score = score;
+					if (best_score == 3)
+						break;				/* no need to look further */
+				}
+			}
+			if (best_score == 3)
+				break;						/* no need to look further */
+		}
+		if (best_score < 0)
+		{
+			/* failed... */
+			ec->ec_broken = true;
+			return NIL;
+		}
+
+		rinfo = build_implied_join_equality(best_eq_op,
+											best_outer_em->em_expr,
+											best_inner_em->em_expr,
+											ec->ec_relids);
+		/* mark restrictinfo as redundant with other joinclauses */
+		rinfo->parent_ec = ec;
+		/* we can set these too, rather than letting them be looked up later */
+		rinfo->left_ec = ec;
+		rinfo->right_ec = ec;
+
+		result = lappend(result, rinfo);
+	}
+
+	/*
+	 * Now deal with building restrictions for any expressions that involve
+	 * Vars from both sides of the join.  We have to equate all of these to
+	 * each other as well as to at least one old member (if any).
+	 *
+	 * XXX as in generate_base_implied_equalities_no_const, we could be a
+	 * lot smarter here to avoid unnecessary failures in cross-type situations.
+	 * For now, use the same left-to-right method used there.
+	 */
+	if (new_members)
+	{
+		List	   *old_members = list_concat(outer_members, inner_members);
+		EquivalenceMember *prev_em = NULL;
+		RestrictInfo *rinfo;
+
+		/* For now, arbitrarily take the first old_member as the one to use */
+		if (old_members)
+			new_members = lappend(new_members, linitial(old_members));
+
+		foreach(lc1, new_members)
+		{
+			EquivalenceMember *cur_em = (EquivalenceMember *) lfirst(lc1);
+
+			if (prev_em != NULL)
+			{
+				Oid			eq_op;
+
+				eq_op = select_equality_operator(ec,
+												 prev_em->em_datatype,
+												 cur_em->em_datatype);
+				if (!OidIsValid(eq_op))
+				{
+					/* failed... */
+					ec->ec_broken = true;
+					return NIL;
+				}
+				rinfo = build_implied_join_equality(eq_op,
+													prev_em->em_expr,
+													cur_em->em_expr,
+													ec->ec_relids);
+
+				/* do NOT set parent_ec, this qual is not redundant! */
+
+				/* we can set these, though */
+				rinfo->left_ec = ec;
+				rinfo->right_ec = ec;
+
+				result = lappend(result, rinfo);
+			}
+			prev_em = cur_em;
+		}
+	}
+
+	return result;
+}
+
+/*
+ * generate_join_implied_equalities cleanup after failure
+ *
+ * Return any original RestrictInfos that are enforceable at this join.
+ */
+static List *
+generate_join_implied_equalities_broken(PlannerInfo *root,
+										EquivalenceClass *ec,
+										RelOptInfo *joinrel,
+										RelOptInfo *outer_rel,
+										RelOptInfo *inner_rel)
+{
+	List	   *result = NIL;
+	ListCell   *lc;
+
+	foreach(lc, ec->ec_sources)
+	{
+		RestrictInfo *restrictinfo = (RestrictInfo *) lfirst(lc);
+
+		if (bms_is_subset(restrictinfo->required_relids, joinrel->relids) &&
+			!bms_is_subset(restrictinfo->required_relids, outer_rel->relids) &&
+			!bms_is_subset(restrictinfo->required_relids, inner_rel->relids))
+			result = lappend(result, restrictinfo);
+	}
+
+	return result;
+}
+
+
+/*
+ * select_equality_operator
+ *	  Select a suitable equality operator for comparing two EC members
+ *
+ * Returns InvalidOid if no operator can be found for this datatype combination
+ */
+static Oid
+select_equality_operator(EquivalenceClass *ec, Oid lefttype, Oid righttype)
+{
+	ListCell   *lc;
+
+	foreach(lc, ec->ec_opfamilies)
+	{
+		Oid		opfamily = lfirst_oid(lc);
+		Oid		opno;
+
+		opno = get_opfamily_member(opfamily, lefttype, righttype,
+								   BTEqualStrategyNumber);
+		if (OidIsValid(opno))
+			return opno;
+	}
+	return InvalidOid;
+}
+
+
+/*
+ * reconsider_outer_join_clauses
+ *	  Re-examine any outer-join clauses that were set aside by
+ *	  distribute_qual_to_rels(), and either create EquivalenceClasses
+ *	  to replace them or push them out into the regular join-clause lists.
+ *
+ * When we have mergejoinable clauses A = B that are outer-join clauses,
+ * we can't blindly combine them with other clauses A = C to deduce B = C,
+ * since in fact the "equality" A = B won't necessarily hold above the
+ * outer join (one of the variables might be NULL instead).  Nonetheless
+ * there are cases where we can add qual clauses using transitivity.
+ *
+ * One case that we look for here is an outer-join clause OUTERVAR = INNERVAR
+ * for which there is also an equivalence clause OUTERVAR = CONSTANT.
+ * It is safe and useful to push a clause INNERVAR = CONSTANT into the
+ * evaluation of the inner (nullable) relation, because any inner rows not
+ * meeting this condition will not contribute to the outer-join result anyway.
+ * (Any outer rows they could join to will be eliminated by the pushed-down
+ * equivalence clause.)
+ *
+ * Note that the above rule does not work for full outer joins; nor is it
+ * very interesting to consider cases where the equivalence clause involves
+ * relations entirely outside the outer join, since such clauses couldn't
+ * be pushed into the inner side's scan anyway.  So the restriction to
+ * outervar = pseudoconstant is not really giving up anything.
+ *
+ * For full-join cases, we can only do something useful if it's a FULL JOIN
+ * USING and a merged column has an equivalence MERGEDVAR = CONSTANT.
+ * By the time it gets here, the merged column will look like
+ *		COALESCE(LEFTVAR, RIGHTVAR)
+ * and we will have a full-join clause LEFTVAR = RIGHTVAR that we can match
+ * the COALESCE expression to. In this situation we can push LEFTVAR = CONSTANT
+ * and RIGHTVAR = CONSTANT into the input relations, since any rows not
+ * meeting these conditions cannot contribute to the join result.
+ *
+ * Again, there isn't any traction to be gained by trying to deal with
+ * clauses comparing a mergedvar to a non-pseudoconstant.  So we can make
+ * use of the EquivalenceClasses to search for matching variables that were
+ * equivalenced to constants.  The interesting outer-join clauses were
+ * accumulated for us by distribute_qual_to_rels.
+ *
+ * When we find one of these cases, we implement the changes we want by
+ * generating a new equivalence clause INNERVAR = CONSTANT (or LEFTVAR, etc)
+ * and pushing it into the EquivalenceClass structures.  This is because we
+ * may already know that INNERVAR is equivalenced to some other var(s), and
+ * we'd like the constant to propagate to them too.  Note that it would be
+ * unsafe to merge any existing EC for INNERVAR with the OUTERVAR's EC ---
+ * that could result in propagating constant restrictions from
+ * INNERVAR to OUTERVAR, which would be very wrong.
+ *
+ * If we don't find any match for a set-aside outer join clause, we must
+ * throw it back into the regular joinclause processing by passing it to
+ * distribute_restrictinfo_to_rels().
+ */
+void
+reconsider_outer_join_clauses(PlannerInfo *root)
+{
+	ListCell   *lc;
+
+	/* Process the LEFT JOIN clauses */
+	foreach(lc, root->left_join_clauses)
+	{
+		RestrictInfo *rinfo = (RestrictInfo *) lfirst(lc);
+
+		reconsider_outer_join_clause(root, rinfo, true);
+	}
+	/* And the RIGHT JOIN clauses */
+	foreach(lc, root->right_join_clauses)
+	{
+		RestrictInfo *rinfo = (RestrictInfo *) lfirst(lc);
+
+		reconsider_outer_join_clause(root, rinfo, false);
+	}
+	/* And the FULL JOIN clauses */
+	foreach(lc, root->full_join_clauses)
+	{
+		RestrictInfo *rinfo = (RestrictInfo *) lfirst(lc);
+
+		reconsider_full_join_clause(root, rinfo);
+	}
+}
+
+/*
+ * reconsider_outer_join_clauses for a single LEFT/RIGHT JOIN clause
+ */
+static void
+reconsider_outer_join_clause(PlannerInfo *root, RestrictInfo *rinfo,
+							 bool outer_on_left)
+{
+	Expr	   *outervar,
+			   *innervar;
+	Oid			left_type,
+				right_type,
+				inner_datatype;
+	ListCell   *lc1;
+
+	/* Extract needed info from the clause */
+	Assert(is_opclause(rinfo->clause));
+	op_input_types(((OpExpr *) rinfo->clause)->opno,
+				   &left_type, &right_type);
+	if (outer_on_left)
+	{
+		outervar = (Expr *) get_leftop(rinfo->clause);
+		innervar = (Expr *) get_rightop(rinfo->clause);
+		inner_datatype = right_type;
+	}
+	else
+	{
+		outervar = (Expr *) get_rightop(rinfo->clause);
+		innervar = (Expr *) get_leftop(rinfo->clause);
+		inner_datatype = left_type;
+	}
+
+	/* Scan EquivalenceClasses for a match to outervar */
+	foreach(lc1, root->eq_classes)
+	{
+		EquivalenceClass *cur_ec = (EquivalenceClass *) lfirst(lc1);
+		bool		match;
+		ListCell   *lc2;
+
+		/* Ignore EC unless it contains pseudoconstants */
+		if (!cur_ec->ec_has_const)
+			continue;
+		/* Never match to a volatile EC */
+		if (cur_ec->ec_has_volatile)
+			continue;
+		/* It has to match the outer-join clause as to opfamilies, too */
+		if (!equal(rinfo->mergeopfamilies, cur_ec->ec_opfamilies))
+			continue;
+		/* Does it contain a match to outervar? */
+		match = false;
+		foreach(lc2, cur_ec->ec_members)
+		{
+			EquivalenceMember *cur_em = (EquivalenceMember *) lfirst(lc2);
+
+			if (equal(outervar, cur_em->em_expr))
+			{
+				match = true;
+				break;
+			}
+		}
+		if (!match)
+			continue;			/* no match, so ignore this EC */
+
+		/*
+		 * Yes it does!  Try to generate a clause INNERVAR = CONSTANT for
+		 * each CONSTANT in the EC.  Note that we must succeed with at
+		 * least one constant before we can decide to throw away the
+		 * outer-join clause.
+		 */
+		match = false;
+		foreach(lc2, cur_ec->ec_members)
+		{
+			EquivalenceMember *cur_em = (EquivalenceMember *) lfirst(lc2);
+			Oid			eq_op;
+			RestrictInfo *newrinfo;
+
+			if (!cur_em->em_is_const)
+				continue;		/* ignore non-const members */
+			eq_op = select_equality_operator(cur_ec,
+											 inner_datatype,
+											 cur_em->em_datatype);
+			if (!OidIsValid(eq_op))
+				continue;		/* can't generate equality */
+			newrinfo = build_implied_join_equality(eq_op,
+												   innervar,
+												   cur_em->em_expr,
+												   cur_ec->ec_relids);
+			if (process_equivalence(root, newrinfo, true))
+				match = true;
+		}
+
+		/*
+		 * If we were able to equate INNERVAR to any constant, we're done, and
+		 * we can throw away the outer-join clause as redundant.  Otherwise,
+		 * fall out of the search loop, since we know the OUTERVAR appears in
+		 * at most one EC.
+		 */
+		if (match)
+			return;
+		else
+			break;
+	}
+
+	/* We did not find a match, so throw it back into regular processing */
+	distribute_restrictinfo_to_rels(root, rinfo);
+}
+
+/*
+ * reconsider_outer_join_clauses for a single FULL JOIN clause
+ */
+static void
+reconsider_full_join_clause(PlannerInfo *root, RestrictInfo *rinfo)
+{
+	Expr	   *leftvar;
+	Expr	   *rightvar;
+	Oid			left_type,
+				right_type;
+	ListCell   *lc1;
+
+	/* Extract needed info from the clause */
+	Assert(is_opclause(rinfo->clause));
+	leftvar = (Expr *) get_leftop(rinfo->clause);
+	rightvar = (Expr *) get_rightop(rinfo->clause);
+	op_input_types(((OpExpr *) rinfo->clause)->opno,
+				   &left_type, &right_type);
+
+	foreach(lc1, root->eq_classes)
+	{
+		EquivalenceClass *cur_ec = (EquivalenceClass *) lfirst(lc1);
+		EquivalenceMember *coal_em = NULL;
+		bool		match;
+		bool		matchleft;
+		bool		matchright;
+		ListCell   *lc2;
+
+		/* Ignore EC unless it contains pseudoconstants */
+		if (!cur_ec->ec_has_const)
+			continue;
+		/* Never match to a volatile EC */
+		if (cur_ec->ec_has_volatile)
+			continue;
+		/* It has to match the outer-join clause as to opfamilies, too */
+		if (!equal(rinfo->mergeopfamilies, cur_ec->ec_opfamilies))
+			continue;
+
+		/*
+		 * Does it contain a COALESCE(leftvar, rightvar) construct?
+		 *
+		 * We can assume the COALESCE() inputs are in the same order as
+		 * the join clause, since both were automatically generated in the
+		 * cases we care about.
+		 *
+		 * XXX currently this may fail to match in cross-type cases
+		 * because the COALESCE will contain typecast operations while the
+		 * join clause may not (if there is a cross-type mergejoin
+		 * operator available for the two column types). Is it OK to strip
+		 * implicit coercions from the COALESCE arguments?
+		 */
+		match = false;
+		foreach(lc2, cur_ec->ec_members)
+		{
+			coal_em = (EquivalenceMember *) lfirst(lc2);
+			if (IsA(coal_em->em_expr, CoalesceExpr))
+			{
+				CoalesceExpr *cexpr = (CoalesceExpr *) coal_em->em_expr;
+				Node	   *cfirst;
+				Node	   *csecond;
+
+				if (list_length(cexpr->args) != 2)
+					continue;
+				cfirst = (Node *) linitial(cexpr->args);
+				csecond = (Node *) lsecond(cexpr->args);
+
+				if (equal(leftvar, cfirst) && equal(rightvar, csecond))
+				{
+					match = true;
+					break;
+				}
+			}
+		}
+		if (!match)
+			continue;			/* no match, so ignore this EC */
+
+		/*
+		 * Yes it does!  Try to generate clauses LEFTVAR = CONSTANT and
+		 * RIGHTVAR = CONSTANT for each CONSTANT in the EC.  Note that we
+		 * must succeed with at least one constant for each var before
+		 * we can decide to throw away the outer-join clause.
+		 */
+		matchleft = matchright = false;
+		foreach(lc2, cur_ec->ec_members)
+		{
+			EquivalenceMember *cur_em = (EquivalenceMember *) lfirst(lc2);
+			Oid			eq_op;
+			RestrictInfo *newrinfo;
+
+			if (!cur_em->em_is_const)
+				continue;		/* ignore non-const members */
+			eq_op = select_equality_operator(cur_ec,
+											 left_type,
+											 cur_em->em_datatype);
+			if (OidIsValid(eq_op))
+			{
+				newrinfo = build_implied_join_equality(eq_op,
+													   leftvar,
+													   cur_em->em_expr,
+													   cur_ec->ec_relids);
+				if (process_equivalence(root, newrinfo, true))
+					matchleft = true;
+			}
+			eq_op = select_equality_operator(cur_ec,
+											 right_type,
+											 cur_em->em_datatype);
+			if (OidIsValid(eq_op))
+			{
+				newrinfo = build_implied_join_equality(eq_op,
+													   rightvar,
+													   cur_em->em_expr,
+													   cur_ec->ec_relids);
+				if (process_equivalence(root, newrinfo, true))
+					matchright = true;
+			}
+		}
+
+		/*
+		 * If we were able to equate both vars to constants, we're done, and
+		 * we can throw away the full-join clause as redundant.  Moreover,
+		 * we can remove the COALESCE entry from the EC, since the added
+		 * restrictions ensure it will always have the expected value.
+		 * (We don't bother trying to update ec_relids or ec_sources.)
+		 */
+		if (matchleft && matchright)
+		{
+			cur_ec->ec_members = list_delete_ptr(cur_ec->ec_members, coal_em);
+			return;
+		}
+		/*
+		 * Otherwise, fall out of the search loop, since we know the COALESCE
+		 * appears in at most one EC (XXX might stop being true if we allow
+		 * stripping of coercions above?)
+		 */
+		break;
+	}
+
+	/* We did not find a match, so throw it back into regular processing */
+	distribute_restrictinfo_to_rels(root, rinfo);
+}
+
+
+/*
+ * exprs_known_equal
+ *	  Detect whether two expressions are known equal due to equivalence
+ *	  relationships.
+ *
+ * Actually, this only shows that the expressions are equal according
+ * to some opfamily's notion of equality --- but we only use it for
+ * selectivity estimation, so a fuzzy idea of equality is OK.
+ *
+ * Note: does not bother to check for "equal(item1, item2)"; caller must
+ * check that case if it's possible to pass identical items.
+ */
+bool
+exprs_known_equal(PlannerInfo *root, Node *item1, Node *item2)
+{
+	ListCell   *lc1;
+
+	foreach(lc1, root->eq_classes)
+	{
+		EquivalenceClass *ec = (EquivalenceClass *) lfirst(lc1);
+		bool		item1member = false;
+		bool		item2member = false;
+		ListCell   *lc2;
+
+		/* Never match to a volatile EC */
+		if (ec->ec_has_volatile)
+			continue;
+
+		foreach(lc2, ec->ec_members)
+		{
+			EquivalenceMember *em = (EquivalenceMember *) lfirst(lc2);
+
+			if (equal(item1, em->em_expr))
+				item1member = true;
+			else if (equal(item2, em->em_expr))
+				item2member = true;
+			/* Exit as soon as equality is proven */
+			if (item1member && item2member)
+				return true;
+		}
+	}
+	return false;
+}
+
+
+/*
+ * add_child_rel_equivalences
+ *	  Search for EC members that reference (only) the parent_rel, and
+ *	  add transformed members referencing the child_rel.
+ *
+ * We only need to do this for ECs that could generate join conditions,
+ * since the child members are only used for creating inner-indexscan paths.
+ *
+ * parent_rel and child_rel could be derived from appinfo, but since the
+ * caller has already computed them, we might as well just pass them in.
+ */
+void
+add_child_rel_equivalences(PlannerInfo *root,
+						   AppendRelInfo *appinfo,
+						   RelOptInfo *parent_rel,
+						   RelOptInfo *child_rel)
+{
+	ListCell   *lc1;
+
+	foreach(lc1, root->eq_classes)
+	{
+		EquivalenceClass *cur_ec = (EquivalenceClass *) lfirst(lc1);
+		ListCell   *lc2;
+
+		/*
+		 * Won't generate joinclauses if const or single-member (the latter
+		 * test covers the volatile case too)
+		 */
+		if (cur_ec->ec_has_const || list_length(cur_ec->ec_members) <= 1)
+			continue;
+
+		/* No point in searching if parent rel not mentioned in eclass */
+		if (!bms_is_subset(parent_rel->relids, cur_ec->ec_relids))
+			continue;
+
+		foreach(lc2, cur_ec->ec_members)
+		{
+			EquivalenceMember *cur_em = (EquivalenceMember *) lfirst(lc2);
+
+			/* Does it reference (only) parent_rel? */
+			if (bms_equal(cur_em->em_relids, parent_rel->relids))
+			{
+				/* Yes, generate transformed child version */
+				Expr *child_expr;
+				
+				child_expr = (Expr *)
+					adjust_appendrel_attrs((Node *) cur_em->em_expr,
+										   appinfo);
+				add_eq_member(cur_ec, child_expr, child_rel->relids,
+							  true, cur_em->em_datatype);
+			}
+		}
+	}
+}
+
+
+/*
+ * find_eclass_clauses_for_index_join
+ *	  Create joinclauses usable for a nestloop-with-inner-indexscan
+ *	  scanning the given inner rel with the specified set of outer rels.
+ */
+List *
+find_eclass_clauses_for_index_join(PlannerInfo *root, RelOptInfo *rel,
+								   Relids outer_relids)
+{
+	List	   *result = NIL;
+	bool		is_child_rel = (rel->reloptkind == RELOPT_OTHER_MEMBER_REL);
+	ListCell   *lc1;
+
+	foreach(lc1, root->eq_classes)
+	{
+		EquivalenceClass *cur_ec = (EquivalenceClass *) lfirst(lc1);
+		ListCell   *lc2;
+
+		/*
+		 * Won't generate joinclauses if const or single-member (the latter
+		 * test covers the volatile case too)
+		 */
+		if (cur_ec->ec_has_const || list_length(cur_ec->ec_members) <= 1)
+			continue;
+
+		/*
+		 * No point in searching if rel not mentioned in eclass (but we
+		 * can't tell that for a child rel).
+		 */
+		if (!is_child_rel &&
+			!bms_is_subset(rel->relids, cur_ec->ec_relids))
+			continue;
+		/* ... nor if no overlap with outer_relids */
+		if (!bms_overlap(outer_relids, cur_ec->ec_relids))
+			continue;
+
+		/* Scan members, looking for indexable columns */
+		foreach(lc2, cur_ec->ec_members)
+		{
+			EquivalenceMember *cur_em = (EquivalenceMember *) lfirst(lc2);
+			EquivalenceMember *best_outer_em = NULL;
+			Oid		best_eq_op = InvalidOid;
+			ListCell   *lc3;
+
+			if (!bms_equal(cur_em->em_relids, rel->relids) ||
+				!eclass_matches_any_index(cur_ec, cur_em, rel))
+				continue;
+
+			/*
+			 * Found one, so try to generate a join clause.  This is like
+			 * generate_join_implied_equalities_normal, except simpler
+			 * since our only preference item is to pick a Var on the
+			 * outer side.  We only need one join clause per index col.
+			 */
+			foreach(lc3, cur_ec->ec_members)
+			{
+				EquivalenceMember *outer_em = (EquivalenceMember *) lfirst(lc3);
+				Oid		eq_op;
+
+				if (!bms_is_subset(outer_em->em_relids, outer_relids))
+					continue;
+				eq_op = select_equality_operator(cur_ec,
+												 cur_em->em_datatype,
+												 outer_em->em_datatype);
+				if (!OidIsValid(eq_op))
+					continue;
+				best_outer_em = outer_em;
+				best_eq_op = eq_op;
+				if (IsA(outer_em->em_expr, Var) ||
+					(IsA(outer_em->em_expr, RelabelType) &&
+					 IsA(((RelabelType *) outer_em->em_expr)->arg, Var)))
+					break;	/* no need to look further */
+			}
+
+			if (best_outer_em)
+			{
+				/* Found a suitable joinclause */
+				RestrictInfo *rinfo;
+
+				rinfo = build_implied_join_equality(best_eq_op,
+													cur_em->em_expr,
+													best_outer_em->em_expr,
+													cur_ec->ec_relids);
+				/* mark restrictinfo as redundant with other joinclauses */
+				rinfo->parent_ec = cur_ec;
+				/* we can set these too */
+				rinfo->left_ec = cur_ec;
+				rinfo->right_ec = cur_ec;
+
+				result = lappend(result, rinfo);
+				/*
+				 * Note: we keep scanning here because we want to provide
+				 * a clause for every possible indexcol.
+				 */
+			}
+		}
+	}
+
+	return result;
+}
+
+
+/*
+ * have_relevant_eclass_joinclause
+ *		Detect whether there is an EquivalenceClass that could produce
+ *		a joinclause between the two given relations.
+ *
+ * This is essentially a very cut-down version of
+ * generate_join_implied_equalities().  Note it's OK to occasionally say "yes"
+ * incorrectly.  Hence we don't bother with details like whether the lack of a
+ * cross-type operator might prevent the clause from actually being generated.
+ */
+bool
+have_relevant_eclass_joinclause(PlannerInfo *root,
+								RelOptInfo *rel1, RelOptInfo *rel2)
+{
+	ListCell   *lc1;
+
+	foreach(lc1, root->eq_classes)
+	{
+		EquivalenceClass *ec = (EquivalenceClass *) lfirst(lc1);
+		bool		has_rel1;
+		bool		has_rel2;
+		ListCell   *lc2;
+
+		/*
+		 * Won't generate joinclauses if const or single-member (the latter
+		 * test covers the volatile case too)
+		 */
+		if (ec->ec_has_const || list_length(ec->ec_members) <= 1)
+			continue;
+
+		/*
+		 * Note we don't test ec_broken; if we did, we'd need a separate code
+		 * path to look through ec_sources.  Checking the members anyway is OK
+		 * as a possibly-overoptimistic heuristic.
+		 */
+
+		/* Needn't scan if it couldn't contain members from each rel */
+		if (!bms_overlap(rel1->relids, ec->ec_relids) ||
+			!bms_overlap(rel2->relids, ec->ec_relids))
+			continue;
+
+		/* Scan the EC to see if it has member(s) in each rel */
+		has_rel1 = has_rel2 = false;
+		foreach(lc2, ec->ec_members)
+		{
+			EquivalenceMember *cur_em = (EquivalenceMember *) lfirst(lc2);
+
+			if (cur_em->em_is_child)
+				continue;			/* ignore children here */
+			if (bms_is_subset(cur_em->em_relids, rel1->relids))
+			{
+				has_rel1 = true;
+				if (has_rel2)
+					break;
+			}
+			if (bms_is_subset(cur_em->em_relids, rel2->relids))
+			{
+				has_rel2 = true;
+				if (has_rel1)
+					break;
+			}
+		}
+
+		if (has_rel1 && has_rel2)
+			return true;
+	}
+
+	return false;
+}
+
+
+/*
+ * has_relevant_eclass_joinclause
+ *		Detect whether there is an EquivalenceClass that could produce
+ *		a joinclause between the given relation and anything else.
+ *
+ * This is the same as have_relevant_eclass_joinclause with the other rel
+ * implicitly defined as "everything else in the query".
+ */
+bool
+has_relevant_eclass_joinclause(PlannerInfo *root, RelOptInfo *rel1)
+{
+	ListCell   *lc1;
+
+	foreach(lc1, root->eq_classes)
+	{
+		EquivalenceClass *ec = (EquivalenceClass *) lfirst(lc1);
+		bool		has_rel1;
+		bool		has_rel2;
+		ListCell   *lc2;
+
+		/*
+		 * Won't generate joinclauses if const or single-member (the latter
+		 * test covers the volatile case too)
+		 */
+		if (ec->ec_has_const || list_length(ec->ec_members) <= 1)
+			continue;
+
+		/*
+		 * Note we don't test ec_broken; if we did, we'd need a separate code
+		 * path to look through ec_sources.  Checking the members anyway is OK
+		 * as a possibly-overoptimistic heuristic.
+		 */
+
+		/* Needn't scan if it couldn't contain members from each rel */
+		if (!bms_overlap(rel1->relids, ec->ec_relids) ||
+			bms_is_subset(ec->ec_relids, rel1->relids))
+			continue;
+
+		/* Scan the EC to see if it has member(s) in each rel */
+		has_rel1 = has_rel2 = false;
+		foreach(lc2, ec->ec_members)
+		{
+			EquivalenceMember *cur_em = (EquivalenceMember *) lfirst(lc2);
+
+			if (cur_em->em_is_child)
+				continue;			/* ignore children here */
+			if (bms_is_subset(cur_em->em_relids, rel1->relids))
+			{
+				has_rel1 = true;
+				if (has_rel2)
+					break;
+			}
+			if (!bms_overlap(cur_em->em_relids, rel1->relids))
+			{
+				has_rel2 = true;
+				if (has_rel1)
+					break;
+			}
+		}
+
+		if (has_rel1 && has_rel2)
+			return true;
+	}
+
+	return false;
+}
+
+
+/*
+ * eclass_useful_for_merging
+ *	  Detect whether the EC could produce any mergejoinable join clauses
+ *	  against the specified relation.
+ *
+ * This is just a heuristic test and doesn't have to be exact; it's better
+ * to say "yes" incorrectly than "no".  Hence we don't bother with details
+ * like whether the lack of a cross-type operator might prevent the clause
+ * from actually being generated.
+ */
+bool
+eclass_useful_for_merging(EquivalenceClass *eclass,
+						  RelOptInfo *rel)
+{
+	ListCell   *lc;
+
+	Assert(!eclass->ec_merged);
+
+	/*
+	 * Won't generate joinclauses if const or single-member (the latter
+	 * test covers the volatile case too)
+	 */
+	if (eclass->ec_has_const || list_length(eclass->ec_members) <= 1)
+		return false;
+
+	/*
+	 * Note we don't test ec_broken; if we did, we'd need a separate code
+	 * path to look through ec_sources.  Checking the members anyway is OK
+	 * as a possibly-overoptimistic heuristic.
+	 */
+
+	/* If rel already includes all members of eclass, no point in searching */
+	if (bms_is_subset(eclass->ec_relids, rel->relids))
+		return false;
+
+	/* To join, we need a member not in the given rel */
+	foreach(lc, eclass->ec_members)
+	{
+		EquivalenceMember *cur_em = (EquivalenceMember *) lfirst(lc);
+
+		if (!cur_em->em_is_child &&
+			!bms_overlap(cur_em->em_relids, rel->relids))
+			return true;
+	}
+
+	return false;
+}