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1. Log retention might not be honored: Log retention is currently at the log segment level, and is driven off the last modification time of a log segment. This approach does not quite work when a replica reassignment happens because the newly created log segment will effectively have its modification time reset to now.
2. Log rolling might break for a newly created replica as well because of the same reason as (1).

Besides that, the KIP will also facilitate some use cases such as streaming processing where a timestamp is needed.

This KIP is a distilled/improved version of an earlier discussion that we started.

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Depending on the use case, user may or may not need to decompress the message to get the CreateTime for each message. Also, with LogAppendTime user can easily get the latency of each message.

Latency Measurement

The latency measurement needs both CreateTime and LogAppendTime. The LogAppendTime does not need to be in the message. Broker now can have a latency metric in for each topic. This could be used for monitoring purpose as well as some application use cases.

A corner case: Leader migration

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