Expand consumer.fetcher comment re comparing request / response offsets

dpkp · dpkp · commit 77360a167fc5 · 2016-07-17T12:00:23.000-07:00
diff --git a/kafka/consumer/fetcher.py b/kafka/consumer/fetcher.py
@@ -683,7 +683,9 @@ def _handle_fetch_response(self, request, send_time, response):
                     self._subscriptions.assignment[tp].highwater = highwater
 
                     # we are interested in this fetch only if the beginning
-                    # offset matches the current consumed position
+                    # offset (of the *request*) matches the current consumed position
+                    # Note that the *response* may return a messageset that starts
+                    # earlier (e.g., compressed messages) or later (e.g., compacted topic)
                     fetch_offset = fetch_offsets[tp]
                     position = self._subscriptions.assignment[tp].position
                     if position is None or position != fetch_offset:
