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In the version 2 format for batch headers, these are the contents that are stored in the headers: the base timestamp and the max timestamp. Each record in the batch contains a timestamp delta which is relative to the base timestamp. In other words, to get the record timestamp, you add the record delta to the base timestamp. Typically there is no reason for the base timestamp to be different from
the timestamp of the first message, but this is not necessarily an iron rule. We can still retrieve the record timestamp if the delta and the base timestamp adds up to it. So the idea is to set the base timestamp to the delete horizon and adjust the deltas accordingly.  

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