These slides from Confluent show that on the new message format the message timestamps will be used to determine the message age. But what are they being compared against? The system time or the stream time?
The documentation says (on Potential breaking changes in 0.10.1.0) that now the log retention is based on "the largest timestamp of the messages in a log segment". Is that what's going to be compared with each message's timestamp or is it compared against the system time to delete the whole segment instead of individual messages?