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last committed offset : last record that consumer has confirmed to have processed.
current position : consumer tracks its current position.
log-end offset : this position advances as consumer advances in the log towards the last record in the partition which is know as the log end offset.
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Mind the Offset Gap or un-committed offsets : between offset 1 et offset 3
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The coordinator is the responsible object for communicating to the cluster and for ensuring the committed offsets are produced into the topic.