Only create fetch requests for ready nodes (#2607)

Author: dpkp

kafka/consumer/fetcher.py

@@ -153,6 +153,7 @@ def send_fetches(self):
             future = self._client.send(node_id, request, wakeup=False)
             future.add_callback(self._handle_fetch_response, node_id, fetch_offsets, time.time())
             future.add_errback(self._handle_fetch_error, node_id)
+            future.add_both(self._clear_pending_fetch_request, node_id)
             futures.append(future)
         self._fetch_futures.extend(futures)
         self._clean_done_fetch_futures()
@@ -643,36 +644,42 @@ def _create_fetch_requests(self):
                 log.debug("Skipping fetch for partition %s because node %s is throttled",
                         partition, node_id)
 
+            elif not self._client.ready(node_id):
+                # Until we support send request queues, any attempt to send to a not-ready node will be
+                # immediately failed with NodeNotReadyError.
+                log.debug("Skipping fetch for partition %s because connection to leader node is not ready yet")
+
             elif node_id in self._nodes_with_pending_fetch_requests:
                 log.debug("Skipping fetch for partition %s because there is a pending fetch request to node %s",
                         partition, node_id)
-                continue
 
-            if version < 5:
-                partition_info = (
-                    partition.partition,
-                    position.offset,
-                    self.config['max_partition_fetch_bytes']
-                )
-            elif version <= 8:
-                partition_info = (
-                    partition.partition,
-                    position.offset,
-                    -1, # log_start_offset is used internally by brokers / replicas only
-                    self.config['max_partition_fetch_bytes'],
-                )
             else:
-                partition_info = (
-                    partition.partition,
-                    position.leader_epoch,
-                    position.offset,
-                    -1, # log_start_offset is used internally by brokers / replicas only
-                    self.config['max_partition_fetch_bytes'],
-                )
-
-            fetchable[node_id][partition] = partition_info
-            log.debug("Adding fetch request for partition %s at offset %d",
-                      partition, position.offset)
+                # Leader is connected and does not have a pending fetch request
+                if version < 5:
+                    partition_info = (
+                        partition.partition,
+                        position.offset,
+                        self.config['max_partition_fetch_bytes']
+                    )
+                elif version <= 8:
+                    partition_info = (
+                        partition.partition,
+                        position.offset,
+                        -1, # log_start_offset is used internally by brokers / replicas only
+                        self.config['max_partition_fetch_bytes'],
+                    )
+                else:
+                    partition_info = (
+                        partition.partition,
+                        position.leader_epoch,
+                        position.offset,
+                        -1, # log_start_offset is used internally by brokers / replicas only
+                        self.config['max_partition_fetch_bytes'],
+                    )
+
+                fetchable[node_id][partition] = partition_info
+                log.debug("Adding fetch request for partition %s at offset %d",
+                          partition, position.offset)
 
         requests = {}
         for node_id, next_partitions in six.iteritems(fetchable):
@@ -761,14 +768,18 @@ def _handle_fetch_response(self, node_id, fetch_offsets, send_time, response):
 
         if self._sensors:
             self._sensors.fetch_latency.record((time.time() - send_time) * 1000)
-        self._nodes_with_pending_fetch_requests.remove(node_id)
 
     def _handle_fetch_error(self, node_id, exception):
         level = logging.INFO if isinstance(exception, Errors.Cancelled) else logging.ERROR
         log.log(level, 'Fetch to node %s failed: %s', node_id, exception)
         if node_id in self._session_handlers:
             self._session_handlers[node_id].handle_error(exception)
-        self._nodes_with_pending_fetch_requests.remove(node_id)
+
+    def _clear_pending_fetch_request(self, node_id, _):
+        try:
+            self._nodes_with_pending_fetch_requests.remove(node_id)
+        except KeyError:
+            pass
 
     def _parse_fetched_data(self, completed_fetch):
         tp = completed_fetch.topic_partition

test/test_fetcher.py

@@ -103,6 +103,7 @@ def test_create_fetch_requests(fetcher, mocker, api_version, fetch_version):
     fetcher._client._api_versions = BROKER_API_VERSIONS[api_version]
     mocker.patch.object(fetcher._client.cluster, "leader_for_partition", return_value=0)
     mocker.patch.object(fetcher._client.cluster, "leader_epoch_for_partition", return_value=0)
+    mocker.patch.object(fetcher._client, "ready", return_value=True)
     by_node = fetcher._create_fetch_requests()
     requests_and_offsets = by_node.values()
     assert set([r.API_VERSION for (r, _offsets) in requests_and_offsets]) == set([fetch_version])