3 files changed, 68 insertions, 0 deletions
diff --git a/contrib/postgres_fdw/expected/postgres_fdw.out b/contrib/postgres_fdw/expected/postgres_fdw.out
index 7d6f7d9e3df..b2e02caefe4 100644
--- a/contrib/postgres_fdw/expected/postgres_fdw.out
+++ b/contrib/postgres_fdw/expected/postgres_fdw.out
@@ -10800,6 +10800,43 @@ DROP TABLE base_tbl1;
 DROP TABLE base_tbl2;
 DROP TABLE result_tbl;
 DROP TABLE join_tbl;
+-- Test that an asynchronous fetch is processed before restarting the scan in
+-- ReScanForeignScan
+CREATE TABLE base_tbl (a int, b int);
+INSERT INTO base_tbl VALUES (1, 11), (2, 22), (3, 33);
+CREATE FOREIGN TABLE foreign_tbl (b int)
+  SERVER loopback OPTIONS (table_name 'base_tbl');
+CREATE FOREIGN TABLE foreign_tbl2 () INHERITS (foreign_tbl)
+  SERVER loopback OPTIONS (table_name 'base_tbl');
+EXPLAIN (VERBOSE, COSTS OFF)
+SELECT a FROM base_tbl WHERE a IN (SELECT a FROM foreign_tbl);
+                                 QUERY PLAN                                  
+-----------------------------------------------------------------------------
+ Seq Scan on public.base_tbl
+   Output: base_tbl.a
+   Filter: (SubPlan 1)
+   SubPlan 1
+     ->  Result
+           Output: base_tbl.a
+           ->  Append
+                 ->  Async Foreign Scan on public.foreign_tbl foreign_tbl_1
+                       Remote SQL: SELECT NULL FROM public.base_tbl
+                 ->  Async Foreign Scan on public.foreign_tbl2 foreign_tbl_2
+                       Remote SQL: SELECT NULL FROM public.base_tbl
+(11 rows)
+
+SELECT a FROM base_tbl WHERE a IN (SELECT a FROM foreign_tbl);
+ a 
+---
+ 1
+ 2
+ 3
+(3 rows)
+
+-- Clean up
+DROP FOREIGN TABLE foreign_tbl CASCADE;
+NOTICE:  drop cascades to foreign table foreign_tbl2
+DROP TABLE base_tbl;
 ALTER SERVER loopback OPTIONS (DROP async_capable);
 ALTER SERVER loopback2 OPTIONS (DROP async_capable);
 -- ===================================================================
diff --git a/contrib/postgres_fdw/postgres_fdw.c b/contrib/postgres_fdw/postgres_fdw.c
index bf3f3d9e26e..56654844e8f 100644
--- a/contrib/postgres_fdw/postgres_fdw.c
+++ b/contrib/postgres_fdw/postgres_fdw.c
@@ -1652,6 +1652,18 @@ postgresReScanForeignScan(ForeignScanState *node)
 		return;
 
 	/*
+	 * If the node is async-capable, and an asynchronous fetch for it has been
+	 * begun, the asynchronous fetch might not have yet completed.  Check if
+	 * the node is async-capable, and an asynchronous fetch for it is still in
+	 * progress; if so, complete the asynchronous fetch before restarting the
+	 * scan.
+	 */
+	if (fsstate->async_capable &&
+		fsstate->conn_state->pendingAreq &&
+		fsstate->conn_state->pendingAreq->requestee == (PlanState *) node)
+		fetch_more_data(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
@@ -6999,6 +7011,8 @@ produce_tuple_asynchronously(AsyncRequest *areq, bool fetch)
 		ExecAsyncRequestDone(areq, result);
 		return;
 	}
+
+	/* We must have run out of tuples */
 	Assert(fsstate->next_tuple >= fsstate->num_tuples);
 
 	/* Fetch some more tuples, if we've not detected EOF yet */
diff --git a/contrib/postgres_fdw/sql/postgres_fdw.sql b/contrib/postgres_fdw/sql/postgres_fdw.sql
index 9eb673e3693..e050639b572 100644
--- a/contrib/postgres_fdw/sql/postgres_fdw.sql
+++ b/contrib/postgres_fdw/sql/postgres_fdw.sql
@@ -3431,6 +3431,23 @@ DROP TABLE base_tbl2;
 DROP TABLE result_tbl;
 DROP TABLE join_tbl;
 
+-- Test that an asynchronous fetch is processed before restarting the scan in
+-- ReScanForeignScan
+CREATE TABLE base_tbl (a int, b int);
+INSERT INTO base_tbl VALUES (1, 11), (2, 22), (3, 33);
+CREATE FOREIGN TABLE foreign_tbl (b int)
+  SERVER loopback OPTIONS (table_name 'base_tbl');
+CREATE FOREIGN TABLE foreign_tbl2 () INHERITS (foreign_tbl)
+  SERVER loopback OPTIONS (table_name 'base_tbl');
+
+EXPLAIN (VERBOSE, COSTS OFF)
+SELECT a FROM base_tbl WHERE a IN (SELECT a FROM foreign_tbl);
+SELECT a FROM base_tbl WHERE a IN (SELECT a FROM foreign_tbl);
+
+-- Clean up
+DROP FOREIGN TABLE foreign_tbl CASCADE;
+DROP TABLE base_tbl;
+
 ALTER SERVER loopback OPTIONS (DROP async_capable);
 ALTER SERVER loopback2 OPTIONS (DROP async_capable);