diff --git a/lib/isc/netmgr/http.c b/lib/isc/netmgr/http.c
index 9a1249feba..eea87aa5d8 100644
--- a/lib/isc/netmgr/http.c
+++ b/lib/isc/netmgr/http.c
@@ -188,6 +188,8 @@ struct isc_nm_http_session {
 	isc__nm_http_pending_callbacks_t pending_write_callbacks;
 	isc_buffer_t *pending_write_data;
 
+	size_t data_in_flight;
+
 	/*
 	 * The statistical values below are for usage on server-side
 	 * only. They are meant to detect clients that are taking too many
@@ -230,7 +232,7 @@ typedef struct isc_http_send_req {
 #define HTTP_HANDLER_MAGIC    ISC_MAGIC('H', 'T', 'H', 'L')
 #define VALID_HTTP_HANDLER(t) ISC_MAGIC_VALID(t, HTTP_HANDLER_MAGIC)
 
-static bool
+static void
 http_send_outgoing(isc_nm_http_session_t *session, isc_nmhandle_t *httphandle,
 		   isc_nm_cb_t cb, void *cbarg);
 
@@ -1054,6 +1056,19 @@ client_submit_request(isc_nm_http_session_t *session, http_cstream_t *stream) {
 	return ISC_R_SUCCESS;
 }
 
+static inline size_t
+http_in_flight_data_size(isc_nm_http_session_t *session) {
+	size_t in_flight = 0;
+
+	if (session->pending_write_data != NULL) {
+		in_flight += isc_buffer_usedlength(session->pending_write_data);
+	}
+
+	in_flight += session->data_in_flight;
+
+	return in_flight;
+}
+
 static ssize_t
 http_process_input_data(isc_nm_http_session_t *session,
 			isc_buffer_t *input_data) {
@@ -1105,13 +1120,14 @@ http_process_input_data(isc_nm_http_session_t *session,
 			(session->received - session->processed);
 
 		/*
-		 * If there are non completed send requests in flight -let's
-		 * not process any incoming data, as it could lead to piling
-		 * up too much send data in send buffers. With many clients
+		 * If there is too much outgoing data in flight - let's not
+		 * process any incoming data, as it could lead to piling up
+		 * too much send data in send buffers. With many clients
 		 * connected it can lead to excessive memory consumption on
 		 * the server instance.
 		 */
-		if (session->sending > 0) {
+		const size_t in_flight = http_in_flight_data_size(session);
+		if (in_flight >= ISC_NETMGR_TCP_SENDBUF_SIZE) {
 			break;
 		}
 
@@ -1320,6 +1336,8 @@ http_writecb(isc_nmhandle_t *handle, isc_result_t result, void *arg) {
 		isc_nmhandle_detach(&req->httphandle);
 	}
 
+	session->data_in_flight -=
+		isc_buffer_usedlength(req->pending_write_data);
 	isc_buffer_free(&req->pending_write_data);
 	session->processed += req->submitted;
 	isc_mem_put(session->mctx, req, sizeof(*req));
@@ -1349,7 +1367,23 @@ move_pending_send_callbacks(isc_nm_http_session_t *session,
 	ISC_LIST_INIT(session->pending_write_callbacks);
 }
 
-static bool
+static inline void
+http_append_pending_send_request(isc_nm_http_session_t *session,
+				 isc_nmhandle_t *httphandle, isc_nm_cb_t cb,
+				 void *cbarg) {
+	REQUIRE(VALID_HTTP2_SESSION(session));
+	REQUIRE(VALID_NMHANDLE(httphandle));
+	REQUIRE(cb != NULL);
+
+	isc__nm_uvreq_t *newcb = isc__nm_uvreq_get(httphandle->sock);
+
+	newcb->cb.send = cb;
+	newcb->cbarg = cbarg;
+	isc_nmhandle_attach(httphandle, &newcb->handle);
+	ISC_LIST_APPEND(session->pending_write_callbacks, newcb, link);
+}
+
+static void
 http_send_outgoing(isc_nm_http_session_t *session, isc_nmhandle_t *httphandle,
 		   isc_nm_cb_t cb, void *cbarg) {
 	isc_http_send_req_t *send = NULL;
@@ -1360,11 +1394,26 @@ http_send_outgoing(isc_nm_http_session_t *session, isc_nmhandle_t *httphandle,
 	size_t max_total_write_size = 0;
 #endif /* ENABLE_HTTP_WRITE_BUFFERING */
 
-	if (!http_session_active(session) ||
-	    (!nghttp2_session_want_write(session->ngsession) &&
-	     session->pending_write_data == NULL))
+	if (!http_session_active(session)) {
+		if (cb != NULL) {
+			isc__nm_uvreq_t *req =
+				isc__nm_uvreq_get(httphandle->sock);
+
+			req->cb.send = cb;
+			req->cbarg = cbarg;
+			isc_nmhandle_attach(httphandle, &req->handle);
+			isc__nm_sendcb(httphandle->sock, req, ISC_R_CANCELED,
+				       true);
+		}
+		return;
+	} else if (!nghttp2_session_want_write(session->ngsession) &&
+		   session->pending_write_data == NULL)
 	{
-		return false;
+		if (cb != NULL) {
+			http_append_pending_send_request(session, httphandle,
+							 cb, cbarg);
+		}
+		return;
 	}
 
 	/*
@@ -1430,16 +1479,8 @@ http_send_outgoing(isc_nm_http_session_t *session, isc_nmhandle_t *httphandle,
 		 * will flush the buffer.
 		 */
 		if (cb != NULL) {
-			isc__nm_uvreq_t *newcb = NULL;
-
-			INSIST(VALID_NMHANDLE(httphandle));
-
-			newcb = isc__nm_uvreq_get(httphandle->sock);
-			newcb->cb.send = cb;
-			newcb->cbarg = cbarg;
-			isc_nmhandle_attach(httphandle, &newcb->handle);
-			ISC_LIST_APPEND(session->pending_write_callbacks, newcb,
-					link);
+			http_append_pending_send_request(session, httphandle,
+							 cb, cbarg);
 		}
 		goto nothing_to_send;
 	} else if (session->sending == 0 && total == 0 &&
@@ -1481,6 +1522,10 @@ http_send_outgoing(isc_nm_http_session_t *session, isc_nmhandle_t *httphandle,
 
 	if (total == 0) {
 		/* No data returned */
+		if (cb != NULL) {
+			http_append_pending_send_request(session, httphandle,
+							 cb, cbarg);
+		}
 		goto nothing_to_send;
 	}
 
@@ -1509,20 +1554,32 @@ http_send_outgoing(isc_nm_http_session_t *session, isc_nmhandle_t *httphandle,
 
 	session->sending++;
 	isc_buffer_usedregion(send->pending_write_data, &send_data);
+	session->data_in_flight += send_data.length;
 	isc_nm_send(transphandle, &send_data, http_writecb, send);
-	return true;
+	return;
 
 nothing_to_send:
 	isc_nmhandle_detach(&transphandle);
-	return false;
 }
 
 static inline bool
 http_too_many_active_streams(isc_nm_http_session_t *session) {
 	const uint64_t active_streams = session->received - session->processed;
+	/*
+	 * The motivation behind capping the maximum active streams number
+	 * to a third of maximum streams is to allow the value to scale
+	 * with the max number of streams.
+	 *
+	 * We do not want to have too many active streams at once as every
+	 * stream is processed as a separate virtual connection by the
+	 * higher level code. If a client sends a bulk of requests without
+	 * waiting for the previous ones to complete we might want to
+	 * throttle it as it might be not a friend knocking at the
+	 * door. We already have some job to do for it.
+	 */
 	const uint64_t max_active_streams =
-		ISC_MIN(ISC_NETMGR_MAX_STREAM_CLIENTS_PER_CONN,
-			session->max_concurrent_streams);
+		ISC_MAX(ISC_NETMGR_MAX_STREAM_CLIENTS_PER_CONN,
+			session->max_concurrent_streams / 3);
 
 	if (session->client) {
 		return false;
@@ -1558,8 +1615,8 @@ http_do_bio(isc_nm_http_session_t *session, isc_nmhandle_t *send_httphandle,
 
 	if (send_cb != NULL) {
 		INSIST(VALID_NMHANDLE(send_httphandle));
-		(void)http_send_outgoing(session, send_httphandle, send_cb,
-					 send_cbarg);
+		http_send_outgoing(session, send_httphandle, send_cb,
+				   send_cbarg);
 		return;
 	}
 
@@ -1568,7 +1625,7 @@ http_do_bio(isc_nm_http_session_t *session, isc_nmhandle_t *send_httphandle,
 	INSIST(send_cbarg == NULL);
 
 	if (session->pending_write_data != NULL && session->sending == 0) {
-		(void)http_send_outgoing(session, NULL, NULL, NULL);
+		http_send_outgoing(session, NULL, NULL, NULL);
 		return;
 	}
 
@@ -1623,8 +1680,7 @@ http_do_bio(isc_nm_http_session_t *session, isc_nmhandle_t *send_httphandle,
 				 */
 				http_do_bio_async(session);
 			} else {
-				(void)http_send_outgoing(session, NULL, NULL,
-							 NULL);
+				http_send_outgoing(session, NULL, NULL, NULL);
 			}
 
 			isc__nm_httpsession_detach(&tmpsess);
@@ -1642,7 +1698,7 @@ http_do_bio(isc_nm_http_session_t *session, isc_nmhandle_t *send_httphandle,
 	}
 
 	/* we might have some data to send after processing */
-	(void)http_send_outgoing(session, NULL, NULL, NULL);
+	http_send_outgoing(session, NULL, NULL, NULL);
 
 	if (nghttp2_session_want_read(session->ngsession) == 0 &&
 	    nghttp2_session_want_write(session->ngsession) == 0 &&