about "PIP 6: Guaranteed Message Deduplication"

[startjava]

https://github.com/apache/pulsar/wiki/PIP-6:-Guaranteed-Message-Deduplication

If the state change from processing the data and the message id associated with the data are updated atomically, then the application can make sure that the state transitions triggered by the messages read from the topic are only applied once.

why "once“？ not can "more"??

"If the state change"，what state？？

@merlimat @sijie

[startjava]

Since with topic reader we can cover the the "message consumption" side, to close the circle we need to ensure that messages are published exactly one time in the topic.

what is "circle",why close it ?