To support KAFKA-560 it would be nice to have a last modified time in the TopicMetadataRequest. This would be the timestamp of the last append to the log as taken from stat on the final log segment.
Implementation would involve
1. Adding a new field to TopicMetadataRequest
2. Adding a method Log.lastModified: Long to get the last modified time from a log
This timestamp would, of course, be subject to error in the event that the file was touched without modification, but I think that is actually okay since it provides a manual way to avoid gc'ing a topic that you know you will want.
It is debatable whether this should go in 0.8. It would be nice to add the field to the metadata request, at least, as that change should be easy and would avoid needing to bump the version in the future.