Fix oversight in commit 1ec7fca8592178281cd5cdada0f27a340fb813fc.

I failed to account for the possibility that when
ExecAppendAsyncEventWait() notifies multiple async-capable nodes using
postgres_fdw, a preceding node might invoke process_pending_request() to
process a pending asynchronous request made by a succeeding node.  In
that case the succeeding node should produce a tuple to return to the
parent Append node from tuples fetched by process_pending_request() when
notified.  Repair.

Per buildfarm via Michael Paquier.  Back-patch to v14, like the previous
commit.

Thanks to Tom Lane for testing.

Discussion: https://postgr.es/m/YQP0UPT8KmPiHTMs%40paquier.xyz

1 files changed, 12 insertions, 10 deletions

diff --git a/src/backend/executor/nodeAppend.c b/src/backend/executor/nodeAppend.c
index a4eef19d7f4..6a2daa6e767 100644
--- a/src/backend/executor/nodeAppend.c
+++ b/src/backend/executor/nodeAppend.c
@@ -1082,16 +1082,18 @@ ExecAppendAsyncEventWait(AppendState *node)
 		{
 			AsyncRequest *areq = (AsyncRequest *) w->user_data;
 
-			/*
-			 * Mark it as no longer needing a callback.  We must do this
-			 * before dispatching the callback in case the callback resets the
-			 * flag.
-			 */
-			Assert(areq->callback_pending);
-			areq->callback_pending = false;
-
-			/* Do the actual work. */
-			ExecAsyncNotify(areq);
+			if (areq->callback_pending)
+			{
+				/*
+				 * Mark it as no longer needing a callback.  We must do this
+				 * before dispatching the callback in case the callback resets
+				 * the flag.
+				 */
+				areq->callback_pending = false;
+
+				/* Do the actual work. */
+				ExecAsyncNotify(areq);
+			}
 		}
 	}
 }