1 files changed, 75 insertions, 28 deletions

diff --git a/contrib/postgres_fdw/postgres_fdw.c b/contrib/postgres_fdw/postgres_fdw.c
index 56654844e8f..c51dd687229 100644
--- a/contrib/postgres_fdw/postgres_fdw.c
+++ b/contrib/postgres_fdw/postgres_fdw.c
@@ -18,6 +18,7 @@
 #include "access/sysattr.h"
 #include "access/table.h"
 #include "catalog/pg_class.h"
+#include "catalog/pg_opfamily.h"
 #include "commands/defrem.h"
 #include "commands/explain.h"
 #include "commands/vacuum.h"
@@ -918,8 +919,6 @@ get_useful_pathkeys_for_relation(PlannerInfo *root, RelOptInfo *rel)
 		foreach(lc, root->query_pathkeys)
 		{
 			PathKey    *pathkey = (PathKey *) lfirst(lc);
-			EquivalenceClass *pathkey_ec = pathkey->pk_eclass;
-			Expr	   *em_expr;
 
 			/*
 			 * The planner and executor don't have any clever strategy for
@@ -927,13 +926,8 @@ get_useful_pathkeys_for_relation(PlannerInfo *root, RelOptInfo *rel)
 			 * getting it to be sorted by all of those pathkeys. We'll just
 			 * end up resorting the entire data set.  So, unless we can push
 			 * down all of the query pathkeys, forget it.
-			 *
-			 * is_foreign_expr would detect volatile expressions as well, but
-			 * checking ec_has_volatile here saves some cycles.
 			 */
-			if (pathkey_ec->ec_has_volatile ||
-				!(em_expr = find_em_expr_for_rel(pathkey_ec, rel)) ||
-				!is_foreign_expr(root, rel, em_expr))
+			if (!is_foreign_pathkey(root, rel, pathkey))
 			{
 				query_pathkeys_ok = false;
 				break;
@@ -980,16 +974,19 @@ get_useful_pathkeys_for_relation(PlannerInfo *root, RelOptInfo *rel)
 	foreach(lc, useful_eclass_list)
 	{
 		EquivalenceClass *cur_ec = lfirst(lc);
-		Expr	   *em_expr;
 		PathKey    *pathkey;
 
 		/* If redundant with what we did above, skip it. */
 		if (cur_ec == query_ec)
 			continue;
 
+		/* Can't push down the sort if the EC's opfamily is not shippable. */
+		if (!is_shippable(linitial_oid(cur_ec->ec_opfamilies),
+						  OperatorFamilyRelationId, fpinfo))
+			continue;
+
 		/* If no pushable expression for this rel, skip it. */
-		em_expr = find_em_expr_for_rel(cur_ec, rel);
-		if (em_expr == NULL || !is_foreign_expr(root, rel, em_expr))
+		if (find_em_for_rel(root, cur_ec, rel) == NULL)
 			continue;
 
 		/* Looks like we can generate a pathkey, so let's do it. */
@@ -6543,7 +6540,6 @@ add_foreign_ordered_paths(PlannerInfo *root, RelOptInfo *input_rel,
 	{
 		PathKey    *pathkey = (PathKey *) lfirst(lc);
 		EquivalenceClass *pathkey_ec = pathkey->pk_eclass;
-		Expr	   *sort_expr;
 
 		/*
 		 * is_foreign_expr would detect volatile expressions as well, but
@@ -6552,13 +6548,20 @@ add_foreign_ordered_paths(PlannerInfo *root, RelOptInfo *input_rel,
 		if (pathkey_ec->ec_has_volatile)
 			return;
 
-		/* Get the sort expression for the pathkey_ec */
-		sort_expr = find_em_expr_for_input_target(root,
-												  pathkey_ec,
-												  input_rel->reltarget);
+		/*
+		 * Can't push down the sort if pathkey's opfamily is not shippable.
+		 */
+		if (!is_shippable(pathkey->pk_opfamily, OperatorFamilyRelationId,
+						  fpinfo))
+			return;
 
-		/* If it's unsafe to remote, we cannot push down the final sort */
-		if (!is_foreign_expr(root, input_rel, sort_expr))
+		/*
+		 * The EC must contain a shippable EM that is computed in input_rel's
+		 * reltarget, else we can't push down the sort.
+		 */
+		if (find_em_for_rel_target(root,
+								   pathkey_ec,
+								   input_rel) == NULL)
 			return;
 	}
 
@@ -7384,14 +7387,55 @@ conversion_error_callback(void *arg)
 }
 
 /*
- * Find an equivalence class member expression to be computed as a sort column
- * in the given target.
+ * Given an EquivalenceClass and a foreign relation, find an EC member
+ * that can be used to sort the relation remotely according to a pathkey
+ * using this EC.
+ *
+ * If there is more than one suitable candidate, return an arbitrary
+ * one of them.  If there is none, return NULL.
+ *
+ * This checks that the EC member expression uses only Vars from the given
+ * rel and is shippable.  Caller must separately verify that the pathkey's
+ * ordering operator is shippable.
+ */
+EquivalenceMember *
+find_em_for_rel(PlannerInfo *root, EquivalenceClass *ec, RelOptInfo *rel)
+{
+	ListCell   *lc;
+
+	foreach(lc, ec->ec_members)
+	{
+		EquivalenceMember *em = (EquivalenceMember *) lfirst(lc);
+
+		/*
+		 * Note we require !bms_is_empty, else we'd accept constant
+		 * expressions which are not suitable for the purpose.
+		 */
+		if (bms_is_subset(em->em_relids, rel->relids) &&
+			!bms_is_empty(em->em_relids) &&
+			is_foreign_expr(root, rel, em->em_expr))
+			return em;
+	}
+
+	return NULL;
+}
+
+/*
+ * Find an EquivalenceClass member that is to be computed as a sort column
+ * in the given rel's reltarget, and is shippable.
+ *
+ * If there is more than one suitable candidate, return an arbitrary
+ * one of them.  If there is none, return NULL.
+ *
+ * This checks that the EC member expression uses only Vars from the given
+ * rel and is shippable.  Caller must separately verify that the pathkey's
+ * ordering operator is shippable.
  */
-Expr *
-find_em_expr_for_input_target(PlannerInfo *root,
-							  EquivalenceClass *ec,
-							  PathTarget *target)
+EquivalenceMember *
+find_em_for_rel_target(PlannerInfo *root, EquivalenceClass *ec,
+					   RelOptInfo *rel)
 {
+	PathTarget *target = rel->reltarget;
 	ListCell   *lc1;
 	int			i;
 
@@ -7434,15 +7478,18 @@ find_em_expr_for_input_target(PlannerInfo *root,
 			while (em_expr && IsA(em_expr, RelabelType))
 				em_expr = ((RelabelType *) em_expr)->arg;
 
-			if (equal(em_expr, expr))
-				return em->em_expr;
+			if (!equal(em_expr, expr))
+				continue;
+
+			/* Check that expression (including relabels!) is shippable */
+			if (is_foreign_expr(root, rel, em->em_expr))
+				return em;
 		}
 
 		i++;
 	}
 
-	elog(ERROR, "could not find pathkey item to sort");
-	return NULL;				/* keep compiler quiet */
+	return NULL;
 }
 
 /*