Add internal update_offsets param to consumer poll(); default to new …

…iterator

kafka/consumer/group.py

@@ -303,7 +303,7 @@ class KafkaConsumer(six.Iterator):
         'sasl_kerberos_service_name': 'kafka',
         'sasl_kerberos_domain_name': None,
         'sasl_oauth_token_provider': None,
-        'legacy_iterator': True, # experimental feature
+        'legacy_iterator': False, # enable to revert to < 1.4.7 iterator
     }
     DEFAULT_SESSION_TIMEOUT_MS_0_9 = 30000
 
@@ -598,7 +598,7 @@ def partitions_for_topic(self, topic):
             partitions = cluster.partitions_for_topic(topic)
         return partitions
 
-    def poll(self, timeout_ms=0, max_records=None):
+    def poll(self, timeout_ms=0, max_records=None, update_offsets=True):
         """Fetch data from assigned topics / partitions.
 
         Records are fetched and returned in batches by topic-partition.
@@ -622,6 +622,12 @@ def poll(self, timeout_ms=0, max_records=None):
             dict: Topic to list of records since the last fetch for the
                 subscribed list of topics and partitions.
         """
+        # Note: update_offsets is an internal-use only argument. It is used to
+        # support the python iterator interface, and which wraps consumer.poll()
+        # and requires that the partition offsets tracked by the fetcher are not
+        # updated until the iterator returns each record to the user. As such,
+        # the argument is not documented and should not be relied on by library
+        # users to not break in the future.
         assert timeout_ms >= 0, 'Timeout must not be negative'
         if max_records is None:
             max_records = self.config['max_poll_records']
@@ -632,7 +638,7 @@ def poll(self, timeout_ms=0, max_records=None):
         start = time.time()
         remaining = timeout_ms
         while True:
-            records = self._poll_once(remaining, max_records)
+            records = self._poll_once(remaining, max_records, update_offsets=update_offsets)
             if records:
                 return records
 
@@ -642,7 +648,7 @@ def poll(self, timeout_ms=0, max_records=None):
             if remaining <= 0:
                 return {}
 
-    def _poll_once(self, timeout_ms, max_records):
+    def _poll_once(self, timeout_ms, max_records, update_offsets=True):
         """Do one round of polling. In addition to checking for new data, this does
         any needed heart-beating, auto-commits, and offset updates.
 
@@ -661,7 +667,7 @@ def _poll_once(self, timeout_ms, max_records):
 
         # If data is available already, e.g. from a previous network client
         # poll() call to commit, then just return it immediately
-        records, partial = self._fetcher.fetched_records(max_records, update_offsets=bool(self._iterator))
+        records, partial = self._fetcher.fetched_records(max_records, update_offsets=update_offsets)
         if records:
             # Before returning the fetched records, we can send off the
             # next round of fetches and avoid block waiting for their
@@ -681,7 +687,7 @@ def _poll_once(self, timeout_ms, max_records):
         if self._coordinator.need_rejoin():
             return {}
 
-        records, _ = self._fetcher.fetched_records(max_records, update_offsets=bool(self._iterator))
+        records, _ = self._fetcher.fetched_records(max_records, update_offsets=update_offsets)
         return records
 
     def position(self, partition):
@@ -1089,7 +1095,7 @@ def _update_fetch_positions(self, partitions):
 
     def _message_generator_v2(self):
         timeout_ms = 1000 * (self._consumer_timeout - time.time())
-        record_map = self.poll(timeout_ms=timeout_ms)
+        record_map = self.poll(timeout_ms=timeout_ms, update_offsets=False)
         for tp, records in six.iteritems(record_map):
             # Generators are stateful, and it is possible that the tp / records
             # here may become stale during iteration -- i.e., we seek to a