bezmax edited a comment on issue #6161: Cloning subscriptions URL: https://github.com/apache/pulsar/issues/6161#issuecomment-580068138 Yes, as I mentioned in my last paragraph, Reader is the only alternative that would work. I would like to avoid using it if possible, as we would need to reimplement full functionality of subscriptions but on the client side, as we need an out-of-order acknowledgements as well. Maybe explaining the full flow of the system (Apache Flink based) would be useful: Message is read from pulsar and sent asynchronously down the processing pipeline. Given that some messages go down the pipeline faster than others - ordering might be lost. At a point of time, a synchronization signal is sent for all processors to "checkpoint" their state changes, similar to a "commit" of a transaction. At this moment our reader needs to ack the messages that have reached the end of the processing pipeline (which again, might miss a few late ones). Every "commit" that the system has made is in theory restorable. That is, for every other component we can say "restore your state from 3 commits before now". Except Pulsar subscriber. In pulsar subscriber the only "commit" I can go back is the set of messages that have been acked by sending a `redeliverUnacked` command. That's where this feature request comes in. By copying a subscription we would essentially be able to make a "snapshot" of the state of subscription that we would be able to go back later if needed. Thanks, hope that clarifies the feature request.
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