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If maxTimestampSoFar is -1, log retention will still be based on last_modification_time. And log rolling will still be based on log create time.

Broker will do the followings following during migration:

1. The broker will create a time index for each segment if the segment does not have one.
   1. For the inactive log segments, the broker will append an entry (last_modification_time_of_the_segment -> offset_of_the_first_message_in_the_segment) to each empty time index.
   2. For the active log segments, the time index file will be left empty.
2. The broker will not rebuild the time index unless the broker had a hard failure during the previous shutdown.

After the entire cluster is migrated to use time based log index for log retention,

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