Hi all, Long days ago I opened a PR to support cumulative acknowledgement for C++ client, but it's controversial about whether should a partitioned consumer acknowledge a message ID cumulatively.
See https://github.com/apache/pulsar/pull/6796 for discussion. Currently, the Java client acknowledges the specific partition of the message ID, while the C++ client just fails when calling `acknowledgeCumulative` on a partitioned topic. However, even if the Java client doesn't fail, it's not user friendly. Assuming users called `acknowledgeCumulative` periodically, there is a chance that some messages of the specific partition has never been passed to the method. For example, a consumer received: P0-M0, P1-M0, P0-M1, P1-M1, P0-M2, P1-M2... And the user acknowledged every two messages, i.e. P0-M0, P0-M1, P0-M2 Eventually, partition 1 has never been acknowledged. User must maintain its own `Map<String, MessageId>` cache for a partitioned topic or multi-topics consumer with the existing `acknowledgeCumulative` API. Should we make it more friendly for users? For example, we can make `acknowledgeCumulative` accept the map to remind users to maintain the map from topic name to message ID: ```java // the key is the partitioned topic name like my-topic-partition-0 void acknowledgeCumulative(Map<String, MessageId> topicToMessageId); ``` For those who don't want to maintain the map by themselves, maybe we can provide a simpler API like: ```java // acknowlegde all latest received messages void acknowledgeCumulative(); ``` and provide an option to enable this behavior. Do you have any suggestion on this idea? I will prepare a proposal if there is no disagreement. Thanks, Yunze
