Cosmetic improvements for code related to partitionwise join.

Move have_partkey_equi_join and match_expr_to_partition_keys to
relnode.c, since they're used only there.  Refactor
build_joinrel_partition_info to split out the code that fills the
joinrel's partition key lists; this doesn't have any non-cosmetic
impact, but it seems like a useful separation of concerns.
Improve assorted nearby comments.

Amit Langote, with a little further editorialization by me

Discussion: https://postgr.es/m/CA+HiwqG2WVUGmLJqtR0tPFhniO=H=9qQ+Z3L_ZC+Y3-EVQHFGg@mail.gmail.com

src/backend/optimizer/path/joinrels.c

@@ -20,7 +20,6 @@
 #include "optimizer/pathnode.h"
 #include "optimizer/paths.h"
 #include "partitioning/partbounds.h"
-#include "utils/lsyscache.h"
 #include "utils/memutils.h"
 
 
@@ -46,8 +45,6 @@ static void try_partitionwise_join(PlannerInfo *root, RelOptInfo *rel1,
 static SpecialJoinInfo *build_child_join_sjinfo(PlannerInfo *root,
 												SpecialJoinInfo *parent_sjinfo,
 												Relids left_relids, Relids right_relids);
-static int	match_expr_to_partition_keys(Expr *expr, RelOptInfo *rel,
-										 bool strict_op);
 
 
 /*
@@ -1573,168 +1570,3 @@ build_child_join_sjinfo(PlannerInfo *root, SpecialJoinInfo *parent_sjinfo,
 
 	return sjinfo;
 }
-
-/*
- * Returns true if there exists an equi-join condition for each pair of
- * partition keys from given relations being joined.
- */
-bool
-have_partkey_equi_join(RelOptInfo *joinrel,
-					   RelOptInfo *rel1, RelOptInfo *rel2,
-					   JoinType jointype, List *restrictlist)
-{
-	PartitionScheme part_scheme = rel1->part_scheme;
-	ListCell   *lc;
-	int			cnt_pks;
-	bool		pk_has_clause[PARTITION_MAX_KEYS];
-	bool		strict_op;
-
-	/*
-	 * This function should be called when the joining relations have same
-	 * partitioning scheme.
-	 */
-	Assert(rel1->part_scheme == rel2->part_scheme);
-	Assert(part_scheme);
-
-	memset(pk_has_clause, 0, sizeof(pk_has_clause));
-	foreach(lc, restrictlist)
-	{
-		RestrictInfo *rinfo = lfirst_node(RestrictInfo, lc);
-		OpExpr	   *opexpr;
-		Expr	   *expr1;
-		Expr	   *expr2;
-		int			ipk1;
-		int			ipk2;
-
-		/* If processing an outer join, only use its own join clauses. */
-		if (IS_OUTER_JOIN(jointype) &&
-			RINFO_IS_PUSHED_DOWN(rinfo, joinrel->relids))
-			continue;
-
-		/* Skip clauses which can not be used for a join. */
-		if (!rinfo->can_join)
-			continue;
-
-		/* Skip clauses which are not equality conditions. */
-		if (!rinfo->mergeopfamilies && !OidIsValid(rinfo->hashjoinoperator))
-			continue;
-
-		opexpr = castNode(OpExpr, rinfo->clause);
-
-		/*
-		 * The equi-join between partition keys is strict if equi-join between
-		 * at least one partition key is using a strict operator. See
-		 * explanation about outer join reordering identity 3 in
-		 * optimizer/README
-		 */
-		strict_op = op_strict(opexpr->opno);
-
-		/* Match the operands to the relation. */
-		if (bms_is_subset(rinfo->left_relids, rel1->relids) &&
-			bms_is_subset(rinfo->right_relids, rel2->relids))
-		{
-			expr1 = linitial(opexpr->args);
-			expr2 = lsecond(opexpr->args);
-		}
-		else if (bms_is_subset(rinfo->left_relids, rel2->relids) &&
-				 bms_is_subset(rinfo->right_relids, rel1->relids))
-		{
-			expr1 = lsecond(opexpr->args);
-			expr2 = linitial(opexpr->args);
-		}
-		else
-			continue;
-
-		/*
-		 * Only clauses referencing the partition keys are useful for
-		 * partitionwise join.
-		 */
-		ipk1 = match_expr_to_partition_keys(expr1, rel1, strict_op);
-		if (ipk1 < 0)
-			continue;
-		ipk2 = match_expr_to_partition_keys(expr2, rel2, strict_op);
-		if (ipk2 < 0)
-			continue;
-
-		/*
-		 * If the clause refers to keys at different ordinal positions, it can
-		 * not be used for partitionwise join.
-		 */
-		if (ipk1 != ipk2)
-			continue;
-
-		/*
-		 * The clause allows partitionwise join if only it uses the same
-		 * operator family as that specified by the partition key.
-		 */
-		if (rel1->part_scheme->strategy == PARTITION_STRATEGY_HASH)
-		{
-			if (!op_in_opfamily(rinfo->hashjoinoperator,
-								part_scheme->partopfamily[ipk1]))
-				continue;
-		}
-		else if (!list_member_oid(rinfo->mergeopfamilies,
-								  part_scheme->partopfamily[ipk1]))
-			continue;
-
-		/* Mark the partition key as having an equi-join clause. */
-		pk_has_clause[ipk1] = true;
-	}
-
-	/* Check whether every partition key has an equi-join condition. */
-	for (cnt_pks = 0; cnt_pks < part_scheme->partnatts; cnt_pks++)
-	{
-		if (!pk_has_clause[cnt_pks])
-			return false;
-	}
-
-	return true;
-}
-
-/*
- * Find the partition key from the given relation matching the given
- * expression. If found, return the index of the partition key, else return -1.
- */
-static int
-match_expr_to_partition_keys(Expr *expr, RelOptInfo *rel, bool strict_op)
-{
-	int			cnt;
-
-	/* This function should be called only for partitioned relations. */
-	Assert(rel->part_scheme);
-
-	/* Remove any relabel decorations. */
-	while (IsA(expr, RelabelType))
-		expr = (Expr *) (castNode(RelabelType, expr))->arg;
-
-	for (cnt = 0; cnt < rel->part_scheme->partnatts; cnt++)
-	{
-		ListCell   *lc;
-
-		Assert(rel->partexprs);
-		foreach(lc, rel->partexprs[cnt])
-		{
-			if (equal(lfirst(lc), expr))
-				return cnt;
-		}
-
-		if (!strict_op)
-			continue;
-
-		/*
-		 * If it's a strict equi-join a NULL partition key on one side will
-		 * not join a NULL partition key on the other side. So, rows with NULL
-		 * partition key from a partition on one side can not join with those
-		 * from a non-matching partition on the other side. So, search the
-		 * nullable partition keys as well.
-		 */
-		Assert(rel->nullable_partexprs);
-		foreach(lc, rel->nullable_partexprs[cnt])
-		{
-			if (equal(lfirst(lc), expr))
-				return cnt;
-		}
-	}
-
-	return -1;
-}

src/backend/optimizer/util/plancat.c

@@ -2250,9 +2250,8 @@ find_partition_scheme(PlannerInfo *root, Relation relation)
 /*
  * set_baserel_partition_key_exprs
  *
- * Builds partition key expressions for the given base relation and sets them
+ * Builds partition key expressions for the given base relation and fills
- * in given RelOptInfo.  Any single column partition keys are converted to Var
+ * rel->partexprs.
- * nodes.  All Var nodes are restamped with the relid of given relation.
  */
 static void
 set_baserel_partition_key_exprs(Relation relation,
@@ -2300,16 +2299,17 @@ set_baserel_partition_key_exprs(Relation relation,
 			lc = lnext(partkey->partexprs, lc);
 		}
 
+		/* Base relations have a single expression per key. */
 		partexprs[cnt] = list_make1(partexpr);
 	}
 
 	rel->partexprs = partexprs;
 
 	/*
-	 * A base relation can not have nullable partition key expressions. We
+	 * A base relation does not have nullable partition key expressions, since
-	 * still allocate array of empty expressions lists to keep partition key
+	 * no outer join is involved.  We still allocate an array of empty
-	 * expression handling code simple. See build_joinrel_partition_info() and
+	 * expression lists to keep partition key expression handling code simple.
-	 * match_expr_to_partition_keys().
+	 * See build_joinrel_partition_info() and match_expr_to_partition_keys().
 	 */
 	rel->nullable_partexprs = (List **) palloc0(sizeof(List *) * partnatts);
 }

src/backend/optimizer/util/relnode.c

@@ -29,6 +29,7 @@
 #include "optimizer/tlist.h"
 #include "partitioning/partbounds.h"
 #include "utils/hsearch.h"
+#include "utils/lsyscache.h"
 
 
 typedef struct JoinHashEntry
@@ -58,6 +59,14 @@ static void add_join_rel(PlannerInfo *root, RelOptInfo *joinrel);
 static void build_joinrel_partition_info(RelOptInfo *joinrel,
 										 RelOptInfo *outer_rel, RelOptInfo *inner_rel,
 										 List *restrictlist, JoinType jointype);
+static bool have_partkey_equi_join(RelOptInfo *joinrel,
+								   RelOptInfo *rel1, RelOptInfo *rel2,
+								   JoinType jointype, List *restrictlist);
+static int	match_expr_to_partition_keys(Expr *expr, RelOptInfo *rel,
+										 bool strict_op);
+static void set_joinrel_partition_key_exprs(RelOptInfo *joinrel,
+											RelOptInfo *outer_rel, RelOptInfo *inner_rel,
+											JoinType jointype);
 static void build_child_join_reltarget(PlannerInfo *root,
 									   RelOptInfo *parentrel,
 									   RelOptInfo *childrel,
@@ -1607,18 +1616,15 @@ find_param_path_info(RelOptInfo *rel, Relids required_outer)
 
 /*
  * build_joinrel_partition_info
- *		If the two relations have same partitioning scheme, their join may be
+ *		Checks if the two relations being joined can use partitionwise join
- *		partitioned and will follow the same partitioning scheme as the joining
+ *		and if yes, initialize partitioning information of the resulting
- *		relations. Set the partition scheme and partition key expressions in
+ *		partitioned join relation.
- *		the join relation.
  */
 static void
 build_joinrel_partition_info(RelOptInfo *joinrel, RelOptInfo *outer_rel,
 							 RelOptInfo *inner_rel, List *restrictlist,
 							 JoinType jointype)
 {
-	int			partnatts;
-	int			cnt;
 	PartitionScheme part_scheme;
 
 	/* Nothing to do if partitionwise join technique is disabled. */
@@ -1672,8 +1678,7 @@ build_joinrel_partition_info(RelOptInfo *joinrel, RelOptInfo *outer_rel,
 
 	/*
 	 * This function will be called only once for each joinrel, hence it
-	 * should not have partition scheme, partition bounds, partition key
+	 * should not have partitioning fields filled yet.
-	 * expressions and array for storing child relations set.
 	 */
 	Assert(!joinrel->part_scheme && !joinrel->partexprs &&
 		   !joinrel->nullable_partexprs && !joinrel->part_rels &&
@@ -1685,11 +1690,10 @@ build_joinrel_partition_info(RelOptInfo *joinrel, RelOptInfo *outer_rel,
 	 */
 	joinrel->part_scheme = part_scheme;
 	joinrel->boundinfo = outer_rel->boundinfo;
-	partnatts = joinrel->part_scheme->partnatts;
-	joinrel->partexprs = (List **) palloc0(sizeof(List *) * partnatts);
-	joinrel->nullable_partexprs =
-		(List **) palloc0(sizeof(List *) * partnatts);
 	joinrel->nparts = outer_rel->nparts;
+	set_joinrel_partition_key_exprs(joinrel, outer_rel, inner_rel, jointype);
+
+	/* part_rels[] will be filled later, but allocate it now */
 	joinrel->part_rels =
 		(RelOptInfo **) palloc0(sizeof(RelOptInfo *) * joinrel->nparts);
 
@@ -1699,34 +1703,205 @@ build_joinrel_partition_info(RelOptInfo *joinrel, RelOptInfo *outer_rel,
 	Assert(outer_rel->consider_partitionwise_join);
 	Assert(inner_rel->consider_partitionwise_join);
 	joinrel->consider_partitionwise_join = true;
+}
+
+/*
+ * have_partkey_equi_join
+ *
+ * Returns true if there exist equi-join conditions involving pairs
+ * of matching partition keys of the relations being joined for all
+ * partition keys.
+ */
+static bool
+have_partkey_equi_join(RelOptInfo *joinrel,
+					   RelOptInfo *rel1, RelOptInfo *rel2,
+					   JoinType jointype, List *restrictlist)
+{
+	PartitionScheme part_scheme = rel1->part_scheme;
+	ListCell   *lc;
+	int			cnt_pks;
+	bool		pk_has_clause[PARTITION_MAX_KEYS];
+	bool		strict_op;
 
 	/*
-	 * Construct partition keys for the join.
+	 * This function must only be called when the joined relations have same
-	 *
+	 * partitioning scheme.
-	 * An INNER join between two partitioned relations can be regarded as
-	 * partitioned by either key expression.  For example, A INNER JOIN B ON
-	 * A.a = B.b can be regarded as partitioned on A.a or on B.b; they are
-	 * equivalent.
-	 *
-	 * For a SEMI or ANTI join, the result can only be regarded as being
-	 * partitioned in the same manner as the outer side, since the inner
-	 * columns are not retained.
-	 *
-	 * An OUTER join like (A LEFT JOIN B ON A.a = B.b) may produce rows with
-	 * B.b NULL. These rows may not fit the partitioning conditions imposed on
-	 * B.b. Hence, strictly speaking, the join is not partitioned by B.b and
-	 * thus partition keys of an OUTER join should include partition key
-	 * expressions from the OUTER side only.  However, because all
-	 * commonly-used comparison operators are strict, the presence of nulls on
-	 * the outer side doesn't cause any problem; they can't match anything at
-	 * future join levels anyway.  Therefore, we track two sets of
-	 * expressions: those that authentically partition the relation
-	 * (partexprs) and those that partition the relation with the exception
-	 * that extra nulls may be present (nullable_partexprs).  When the
-	 * comparison operator is strict, the latter is just as good as the
-	 * former.
 	 */
-	for (cnt = 0; cnt < partnatts; cnt++)
+	Assert(rel1->part_scheme == rel2->part_scheme);
+	Assert(part_scheme);
+
+	memset(pk_has_clause, 0, sizeof(pk_has_clause));
+	foreach(lc, restrictlist)
+	{
+		RestrictInfo *rinfo = lfirst_node(RestrictInfo, lc);
+		OpExpr	   *opexpr;
+		Expr	   *expr1;
+		Expr	   *expr2;
+		int			ipk1;
+		int			ipk2;
+
+		/* If processing an outer join, only use its own join clauses. */
+		if (IS_OUTER_JOIN(jointype) &&
+			RINFO_IS_PUSHED_DOWN(rinfo, joinrel->relids))
+			continue;
+
+		/* Skip clauses which can not be used for a join. */
+		if (!rinfo->can_join)
+			continue;
+
+		/* Skip clauses which are not equality conditions. */
+		if (!rinfo->mergeopfamilies && !OidIsValid(rinfo->hashjoinoperator))
+			continue;
+
+		/* Should be OK to assume it's an OpExpr. */
+		opexpr = castNode(OpExpr, rinfo->clause);
+
+		/* Match the operands to the relation. */
+		if (bms_is_subset(rinfo->left_relids, rel1->relids) &&
+			bms_is_subset(rinfo->right_relids, rel2->relids))
+		{
+			expr1 = linitial(opexpr->args);
+			expr2 = lsecond(opexpr->args);
+		}
+		else if (bms_is_subset(rinfo->left_relids, rel2->relids) &&
+				 bms_is_subset(rinfo->right_relids, rel1->relids))
+		{
+			expr1 = lsecond(opexpr->args);
+			expr2 = linitial(opexpr->args);
+		}
+		else
+			continue;
+
+		/*
+		 * Now we need to know whether the join operator is strict; see
+		 * comments in pathnodes.h.
+		 */
+		strict_op = op_strict(opexpr->opno);
+
+		/*
+		 * Only clauses referencing the partition keys are useful for
+		 * partitionwise join.
+		 */
+		ipk1 = match_expr_to_partition_keys(expr1, rel1, strict_op);
+		if (ipk1 < 0)
+			continue;
+		ipk2 = match_expr_to_partition_keys(expr2, rel2, strict_op);
+		if (ipk2 < 0)
+			continue;
+
+		/*
+		 * If the clause refers to keys at different ordinal positions, it can
+		 * not be used for partitionwise join.
+		 */
+		if (ipk1 != ipk2)
+			continue;
+
+		/*
+		 * The clause allows partitionwise join only if it uses the same
+		 * operator family as that specified by the partition key.
+		 */
+		if (rel1->part_scheme->strategy == PARTITION_STRATEGY_HASH)
+		{
+			if (!OidIsValid(rinfo->hashjoinoperator) ||
+				!op_in_opfamily(rinfo->hashjoinoperator,
+								part_scheme->partopfamily[ipk1]))
+				continue;
+		}
+		else if (!list_member_oid(rinfo->mergeopfamilies,
+								  part_scheme->partopfamily[ipk1]))
+			continue;
+
+		/* Mark the partition key as having an equi-join clause. */
+		pk_has_clause[ipk1] = true;
+	}
+
+	/* Check whether every partition key has an equi-join condition. */
+	for (cnt_pks = 0; cnt_pks < part_scheme->partnatts; cnt_pks++)
+	{
+		if (!pk_has_clause[cnt_pks])
+			return false;
+	}
+
+	return true;
+}
+
+/*
+ * match_expr_to_partition_keys
+ *
+ * Tries to match an expression to one of the nullable or non-nullable
+ * partition keys of "rel".  Returns the matched key's ordinal position,
+ * or -1 if the expression could not be matched to any of the keys.
+ *
+ * strict_op must be true if the expression will be compared with the
+ * partition key using a strict operator.  This allows us to consider
+ * nullable as well as nonnullable partition keys.
+ */
+static int
+match_expr_to_partition_keys(Expr *expr, RelOptInfo *rel, bool strict_op)
+{
+	int			cnt;
+
+	/* This function should be called only for partitioned relations. */
+	Assert(rel->part_scheme);
+	Assert(rel->partexprs);
+	Assert(rel->nullable_partexprs);
+
+	/* Remove any relabel decorations. */
+	while (IsA(expr, RelabelType))
+		expr = (Expr *) (castNode(RelabelType, expr))->arg;
+
+	for (cnt = 0; cnt < rel->part_scheme->partnatts; cnt++)
+	{
+		ListCell   *lc;
+
+		/* We can always match to the non-nullable partition keys. */
+		foreach(lc, rel->partexprs[cnt])
+		{
+			if (equal(lfirst(lc), expr))
+				return cnt;
+		}
+
+		if (!strict_op)
+			continue;
+
+		/*
+		 * If it's a strict join operator then a NULL partition key on one
+		 * side will not join to any partition key on the other side, and in
+		 * particular such a row can't join to a row from a different
+		 * partition on the other side.  So, it's okay to search the nullable
+		 * partition keys as well.
+		 */
+		foreach(lc, rel->nullable_partexprs[cnt])
+		{
+			if (equal(lfirst(lc), expr))
+				return cnt;
+		}
+	}
+
+	return -1;
+}
+
+/*
+ * set_joinrel_partition_key_exprs
+ *		Initialize partition key expressions for a partitioned joinrel.
+ */
+static void
+set_joinrel_partition_key_exprs(RelOptInfo *joinrel,
+								RelOptInfo *outer_rel, RelOptInfo *inner_rel,
+								JoinType jointype)
+{
+	int			partnatts = joinrel->part_scheme->partnatts;
+
+	joinrel->partexprs = (List **) palloc0(sizeof(List *) * partnatts);
+	joinrel->nullable_partexprs =
+		(List **) palloc0(sizeof(List *) * partnatts);
+
+	/*
+	 * The joinrel's partition expressions are the same as those of the input
+	 * rels, but we must properly classify them as nullable or not in the
+	 * joinrel's output.
+	 */
+	for (int cnt = 0; cnt < partnatts; cnt++)
 	{
 		/* mark these const to enforce that we copy them properly */
 		const List *outer_expr = outer_rel->partexprs[cnt];
@@ -1738,18 +1913,41 @@ build_joinrel_partition_info(RelOptInfo *joinrel, RelOptInfo *outer_rel,
 
 		switch (jointype)
 		{
+				/*
+				 * A join relation resulting from an INNER join may be
+				 * regarded as partitioned by either of the inner and outer
+				 * relation keys.  For example, A INNER JOIN B ON A.a = B.b
+				 * can be regarded as partitioned on either A.a or B.b.  So we
+				 * add both keys to the joinrel's partexpr lists.  However,
+				 * anything that was already nullable still has to be treated
+				 * as nullable.
+				 */
 			case JOIN_INNER:
 				partexpr = list_concat_copy(outer_expr, inner_expr);
 				nullable_partexpr = list_concat_copy(outer_null_expr,
 													 inner_null_expr);
 				break;
 
+				/*
+				 * A join relation resulting from a SEMI or ANTI join may be
+				 * regarded as partitioned by the outer relation keys.  The
+				 * inner relation's keys are no longer interesting; since they
+				 * aren't visible in the join output, nothing could join to
+				 * them.
+				 */
 			case JOIN_SEMI:
 			case JOIN_ANTI:
 				partexpr = list_copy(outer_expr);
 				nullable_partexpr = list_copy(outer_null_expr);
 				break;
 
+				/*
+				 * A join relation resulting from a LEFT OUTER JOIN likewise
+				 * may be regarded as partitioned on the (non-nullable) outer
+				 * relation keys.  The inner (nullable) relation keys are okay
+				 * as partition keys for further joins as long as they involve
+				 * strict join operators.
+				 */
 			case JOIN_LEFT:
 				partexpr = list_copy(outer_expr);
 				nullable_partexpr = list_concat_copy(inner_expr,
@@ -1758,6 +1956,12 @@ build_joinrel_partition_info(RelOptInfo *joinrel, RelOptInfo *outer_rel,
 												inner_null_expr);
 				break;
 
+				/*
+				 * For FULL OUTER JOINs, both relations are nullable, so the
+				 * resulting join relation may be regarded as partitioned on
+				 * either of inner and outer relation keys, but only for joins
+				 * that involve strict join operators.
+				 */
 			case JOIN_FULL:
 				nullable_partexpr = list_concat_copy(outer_expr,
 													 inner_expr);
@@ -1769,7 +1973,6 @@ build_joinrel_partition_info(RelOptInfo *joinrel, RelOptInfo *outer_rel,
 
 			default:
 				elog(ERROR, "unrecognized join type: %d", (int) jointype);
-
 		}
 
 		joinrel->partexprs[cnt] = partexpr;

src/include/nodes/pathnodes.h

@@ -574,6 +574,24 @@ typedef struct PartitionSchemeData *PartitionScheme;
  * we know we will need it at least once (to price the sequential scan)
  * and may need it multiple times to price index scans.
  *
+ * A join relation is considered to be partitioned if it is formed from a
+ * join of two relations that are partitioned, have matching partitioning
+ * schemes, and are joined on an equijoin of the partitioning columns.
+ * Under those conditions we can consider the join relation to be partitioned
+ * by either relation's partitioning keys, though some care is needed if
+ * either relation can be forced to null by outer-joining.  For example, an
+ * outer join like (A LEFT JOIN B ON A.a = B.b) may produce rows with B.b
+ * NULL.  These rows may not fit the partitioning conditions imposed on B.
+ * Hence, strictly speaking, the join is not partitioned by B.b and thus
+ * partition keys of an outer join should include partition key expressions
+ * from the non-nullable side only.  However, if a subsequent join uses
+ * strict comparison operators (and all commonly-used equijoin operators are
+ * strict), the presence of nulls doesn't cause a problem: such rows couldn't
+ * match anything on the other side and thus they don't create a need to do
+ * any cross-partition sub-joins.  Hence we can treat such values as still
+ * partitioning the join output for the purpose of additional partitionwise
+ * joining, so long as a strict join operator is used by the next join.
+ *
  * If the relation is partitioned, these fields will be set:
  *
  *		part_scheme - Partitioning scheme of the relation
@@ -586,16 +604,15 @@ typedef struct PartitionSchemeData *PartitionScheme;
  *								 this relation that are partitioned tables
  *								 themselves, in hierarchical order
  *
- * Note: A base relation always has only one set of partition keys, but a join
+ * The partexprs and nullable_partexprs arrays each contain
- * relation may have as many sets of partition keys as the number of relations
+ * part_scheme->partnatts elements.  Each of the elements is a list of
- * being joined. partexprs and nullable_partexprs are arrays containing
+ * partition key expressions.  For partitioned base relations, there is one
- * part_scheme->partnatts elements each. Each of these elements is a list of
+ * expression in each partexprs element, and nullable_partexprs is empty.
- * partition key expressions.  For a base relation each list in partexprs
+ * For partitioned join relations, each base relation within the join
- * contains only one expression and nullable_partexprs is not populated. For a
+ * contributes one partition key expression per partitioning column;
- * join relation, partexprs and nullable_partexprs contain partition key
+ * that expression goes in the partexprs[i] list if the base relation
- * expressions from non-nullable and nullable relations resp. Lists at any
+ * is not nullable by this join or any lower outer join, or in the
- * given position in those arrays together contain as many elements as the
+ * nullable_partexprs[i] list if the base relation is nullable.
- * number of joining relations.
  *----------
  */
 typedef enum RelOptKind
@@ -716,16 +733,16 @@ typedef struct RelOptInfo
 	Relids		top_parent_relids;	/* Relids of topmost parents (if "other"
 									 * rel) */
 
-	/* used for partitioned relations */
+	/* used for partitioned relations: */
-	PartitionScheme part_scheme;	/* Partitioning scheme. */
+	PartitionScheme part_scheme;	/* Partitioning scheme */
-	int			nparts;			/* number of partitions */
+	int			nparts;			/* Number of partitions */
 	struct PartitionBoundInfoData *boundinfo;	/* Partition bounds */
-	List	   *partition_qual; /* partition constraint */
+	List	   *partition_qual; /* Partition constraint, if not the root */
 	struct RelOptInfo **part_rels;	/* Array of RelOptInfos of partitions,
-									 * stored in the same order of bounds */
+									 * stored in the same order as bounds */
-	List	  **partexprs;		/* Non-nullable partition key expressions. */
+	List	  **partexprs;		/* Non-nullable partition key expressions */
-	List	  **nullable_partexprs; /* Nullable partition key expressions. */
+	List	  **nullable_partexprs; /* Nullable partition key expressions */
-	List	   *partitioned_child_rels; /* List of RT indexes. */
+	List	   *partitioned_child_rels; /* List of RT indexes */
 } RelOptInfo;
 
 /*

src/include/optimizer/paths.h

@@ -106,9 +106,6 @@ extern bool have_join_order_restriction(PlannerInfo *root,
 extern bool have_dangerous_phv(PlannerInfo *root,
 							   Relids outer_relids, Relids inner_params);
 extern void mark_dummy_rel(RelOptInfo *rel);
-extern bool have_partkey_equi_join(RelOptInfo *joinrel,
-								   RelOptInfo *rel1, RelOptInfo *rel2,
-								   JoinType jointype, List *restrictlist);
 
 /*
  * equivclass.c