One idea that has occasionally been thrown around is allowing topics to be hierarchical. The primary goal was just to allow logical grouping as well as to make it easier to subscribe via a wildcard (it may be easier to give /search/* rather than (search_click|search_result|...)).
Another problem we have seen is that it can be a pain for people to physically locate which cluster has their data since we segregate a few use cases onto separate clusters. It would be nice to have a federated namespace that puts all of these on a single directory tree. Both of these problems kind of arise from having lots and lots of topics and lots of people using the system so they may not be interesting to everyone. Nonetheless I wrote up a quick wiki capturing various thoughts people had thrown around on previous mailing list discussions: https://cwiki.apache.org/confluence/display/KAFKA/Hierarchical+Topics The linkedin folks are pretty busy with replication so i doubt we would work on this in the very near future. -Jay
