[GitHub] [pulsar] merlimat commented on pull request #6796: Support cumulative acknowledgement when consuming partitioned topics for C++ client

[GitBox <gi...@apache.org>]

merlimat commented on pull request #6796:
URL: https://github.com/apache/pulsar/pull/6796#issuecomment-618600371


   > acknowledgementCumulative on a partitioned topic means acknowledging cumulative the messages of the partition inferred by the MessageId.
   
   If I'm consuming from a partitioned topic, I'll get a single stream of messages from multiple partitions.
   
   Eg. `P1_M1`, `P2_M1`, `P2_M2`, `P1_M2`. 
   
   Calling cumulative ack on `P1_M2` would be semantically completely different in the case of partitioned/non-partitioned case.
   
   If you're consuming these messages, and say, acking cumulative every 1 second, you might never be acking on some of the partitions.
   
   The only way for the cumulative ack to make sense with partitions is if the client lib would be keeping track, for a given message id, of all the highest message ids in the other partitions that we were queued before it in the shared queue.


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