fix-rescan-in-postgres-fdw.patch

diff --git a/contrib/postgres_fdw/expected/postgres_fdw.out b/contrib/postgres_fdw/expected/postgres_fdw.out
index 1f22309194..b56cdc4492 100644
--- a/contrib/postgres_fdw/expected/postgres_fdw.out
+++ b/contrib/postgres_fdw/expected/postgres_fdw.out
@@ -6849,6 +6849,49 @@ SELECT * FROM ft1 ORDER BY c6 ASC NULLS FIRST, c1 OFFSET 15 LIMIT 10;
    40 |  42 | 00040_trig_update | Tue Feb 10 00:00:00 1970 PST | Tue Feb 10 00:00:00 1970 | 0    | 0          | foo
 (10 rows)
 
+CREATE TABLE loct1 (c1 int);
+CREATE TABLE loct2 (c1 int, c2 text);
+INSERT INTO loct1 VALUES (1001);
+INSERT INTO loct1 VALUES (1002);
+INSERT INTO loct2 SELECT id, to_char(id, 'FM0000') FROM generate_series(1, 1000) id;
+INSERT INTO loct2 VALUES (1001, 'foo');
+INSERT INTO loct2 VALUES (1002, 'bar');
+CREATE FOREIGN TABLE remt2 (c1 int, c2 text) SERVER loopback OPTIONS (table_name 'loct2');
+ANALYZE loct1;
+ANALYZE remt2;
+SET enable_mergejoin TO false;
+SET enable_hashjoin TO false;
+SET enable_material TO false;
+EXPLAIN (VERBOSE, COSTS OFF)
+UPDATE remt2 SET c2 = remt2.c2 || remt2.c2 FROM loct1 WHERE loct1.c1 = remt2.c1 RETURNING remt2.*;
+                                   QUERY PLAN                                   
+--------------------------------------------------------------------------------
+ Update on public.remt2
+   Output: remt2.c1, remt2.c2
+   Remote SQL: UPDATE public.loct2 SET c2 = $2 WHERE ctid = $1 RETURNING c1, c2
+   ->  Nested Loop
+         Output: (remt2.c2 || remt2.c2), remt2.ctid, remt2.*, loct1.ctid
+         Join Filter: (remt2.c1 = loct1.c1)
+         ->  Seq Scan on public.loct1
+               Output: loct1.ctid, loct1.c1
+         ->  Foreign Scan on public.remt2
+               Output: remt2.c2, remt2.ctid, remt2.*, remt2.c1
+               Remote SQL: SELECT c1, c2, ctid FROM public.loct2 FOR UPDATE
+(11 rows)
+
+UPDATE remt2 SET c2 = remt2.c2 || remt2.c2 FROM loct1 WHERE loct1.c1 = remt2.c1 RETURNING remt2.*;
+  c1  |   c2   
+------+--------
+ 1001 | foofoo
+ 1002 | barbar
+(2 rows)
+
+RESET enable_mergejoin;
+RESET enable_hashjoin;
+RESET enable_material;
+DROP FOREIGN TABLE remt2;
+DROP TABLE loct1;
+DROP TABLE loct2;
 -- ===================================================================
 -- test check constraints
 -- ===================================================================
diff --git a/contrib/postgres_fdw/postgres_fdw.c b/contrib/postgres_fdw/postgres_fdw.c
index 0bb9a5ae8f..fc65d81e21 100644
--- a/contrib/postgres_fdw/postgres_fdw.c
+++ b/contrib/postgres_fdw/postgres_fdw.c
@@ -1662,9 +1662,12 @@ postgresReScanForeignScan(ForeignScanState *node)
 
 	/*
 	 * If any internal parameters affecting this node have changed, we'd
-	 * better destroy and recreate the cursor.  Otherwise, rewinding it should
-	 * be good enough.  If we've only fetched zero or one batch, we needn't
-	 * even rewind the cursor, just rescan what we have.
+	 * better destroy and recreate the cursor.  Otherwise, if the remote
+	 * server is v14 or older, rewinding it should be good enough; if not,
+	 * rewind is only allowed for scrollable cursors, but we don't have a way
+	 * to check the scrollability of it, so destroy and recreate it in any
+	 * case.  If we've only fetched zero or one batch, we needn't even rewind
+	 * the cursor, just rescan what we have.
 	 */
 	if (node->ss.ps.chgParam != NULL)
 	{
@@ -1674,8 +1677,15 @@ postgresReScanForeignScan(ForeignScanState *node)
 	}
 	else if (fsstate->fetch_ct_2 > 1)
 	{
-		snprintf(sql, sizeof(sql), "MOVE BACKWARD ALL IN c%u",
-				 fsstate->cursor_number);
+		if (PQserverVersion(fsstate->conn) < 150000)
+			snprintf(sql, sizeof(sql), "MOVE BACKWARD ALL IN c%u",
+					 fsstate->cursor_number);
+		else
+		{
+			fsstate->cursor_exists = false;
+			snprintf(sql, sizeof(sql), "CLOSE c%u",
+					 fsstate->cursor_number);
+		}
 	}
 	else
 	{
diff --git a/contrib/postgres_fdw/sql/postgres_fdw.sql b/contrib/postgres_fdw/sql/postgres_fdw.sql
index b57f8cfda6..73524ed9e3 100644
--- a/contrib/postgres_fdw/sql/postgres_fdw.sql
+++ b/contrib/postgres_fdw/sql/postgres_fdw.sql
@@ -1647,6 +1647,29 @@ SELECT * FROM ft1 ORDER BY c6 DESC NULLS FIRST, c1 OFFSET 15 LIMIT 10;
 EXPLAIN (VERBOSE, COSTS OFF) SELECT * FROM ft1 ORDER BY c6 ASC NULLS FIRST, c1 OFFSET 15 LIMIT 10;
 SELECT * FROM ft1 ORDER BY c6 ASC NULLS FIRST, c1 OFFSET 15 LIMIT 10;
 
+CREATE TABLE loct1 (c1 int);
+CREATE TABLE loct2 (c1 int, c2 text);
+INSERT INTO loct1 VALUES (1001);
+INSERT INTO loct1 VALUES (1002);
+INSERT INTO loct2 SELECT id, to_char(id, 'FM0000') FROM generate_series(1, 1000) id;
+INSERT INTO loct2 VALUES (1001, 'foo');
+INSERT INTO loct2 VALUES (1002, 'bar');
+CREATE FOREIGN TABLE remt2 (c1 int, c2 text) SERVER loopback OPTIONS (table_name 'loct2');
+ANALYZE loct1;
+ANALYZE remt2;
+SET enable_mergejoin TO false;
+SET enable_hashjoin TO false;
+SET enable_material TO false;
+EXPLAIN (VERBOSE, COSTS OFF)
+UPDATE remt2 SET c2 = remt2.c2 || remt2.c2 FROM loct1 WHERE loct1.c1 = remt2.c1 RETURNING remt2.*;
+UPDATE remt2 SET c2 = remt2.c2 || remt2.c2 FROM loct1 WHERE loct1.c1 = remt2.c1 RETURNING remt2.*;
+RESET enable_mergejoin;
+RESET enable_hashjoin;
+RESET enable_material;
+DROP FOREIGN TABLE remt2;
+DROP TABLE loct1;
+DROP TABLE loct2;
+
 -- ===================================================================
 -- test check constraints
 -- ===================================================================