[mpercy]

Interesting. Just last year we implemented improved re-replication (https://github.com/apache/kudu/commit/79a255) which sounds very similar to what you did with LEARNER roles, and we added manually-triggered rebalancing (https://github.com/apache/kudu/commit/ccdcf6 and https://kudu.apache.org/releases/1.8.0/docs/administration.h...).

I'm curious if you did anything to prevent automatic rebalancing from being triggered at a "bad time" or have throttled it in some way, or whether moving large amounts of data between servers at arbitrary times was not a concern.

I am also curious if you added some type of API using the LEARNER role to support a CDC-type of listener interface using consensus.

By the way, we also recently added support for rack/location awareness in a series of patches including https://github.com/apache/kudu/commit/ebb285

We should really start some threads on the dev lists to periodically share this type of information and merge things back and forth to avoid duplicating work where possible. I know the systems are pretty different at the catalog and storage layers but there are still many similarities.