codelipenghui commented on issue #5719: Remove cursor while remove non-durable subscription URL: https://github.com/apache/pulsar/pull/5719#issuecomment-557966126 We need an approach related to seek position, current approach will close all consumers while seek position happens, but this PR will remove the non-durable cursor while all consumers of the non-durable subscription are disconnected. So the reconnected consumer will create a new non-durable cursor using last message id, the unit test can't passed. It's better to have an approach to handle the position seek, there are two point we need to careful handling: 1. Consumers acknowledge by `outstanding` message ids 2. Avoid consumer to process the `outstanding` messages Here, the outstanding messages means messages already dispatched to consumers but the cursor is reset. For the first point, i think we can use the `read position`, the `read position` always larger than the mark delete position except the cursor reset happens, so if the broker ignore the acknowledge requests which the acknowledge position is larger than `read position`, because there is cursor reset happens. For the second point, if the consumer cache to many outstanding messages, it's waste of resources if process all of these messages, so it's better to send a cursor reseted notify to consumers before dispatch messages after the cursor reset to consumers, consumers can reset their stat, clear the outstanding messages. currently close consumers also can reset consumer state, clear outstanding messages. And in https://github.com/apache/pulsar/pull/5278, we also have discussed about the reset consumer state when cursor reset happens. For this PR, i think we can don't close the readers first, and then create a new PR to improve cursor reset since it might need to change the wire protocol.
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