Allow COPY always continue

src/backend/distributed/commands/multi_copy.c

@@ -3425,6 +3425,15 @@ CopyGetPlacementConnection(ShardPlacement *placement, bool stopOnFailure)
 		MultiShardConnectionType != SEQUENTIAL_CONNECTION)
 	{
 		connectionFlags |= CONNECTION_PER_PLACEMENT;
+
+		/*
+		 * Via connection throttling, the connection establishments may be suspended
+		 * until a connection slot is empty to the remote host. When forced to use
+		 * one connection per placement, do not enforce this restriction as it could
+		 * deadlock against concurrent operation where each operation is blocked on
+		 * waiting for others.
+		 */
+		connectionFlags |= NEVER_WAIT_FOR_CONNECTION;
 	}
 
 	connection = GetPlacementConnection(connectionFlags, placement, nodeUser);

src/backend/distributed/executor/adaptive_executor.c

@@ -2400,7 +2400,9 @@ ManageWorkerPool(WorkerPool *workerPool)
 			/*
 			 * Via connection throttling, the connection establishments may be suspended
 			 * until a connection slot is empty to the remote host. When forced to use
-			 * one connection per placement, do not enforce this restriction.
+			 * one connection per placement, do not enforce this restriction as it could
+			 * deadlock against concurrent operation where each operation is blocked on
+			 * waiting for others.
 			 */
 			connectionFlags |= NEVER_WAIT_FOR_CONNECTION;
 		}