My understanding of hbase (which could be wrong) is that writes of a particular key always go to the region master first, so if you read from the master you always get the latest value of a key. The tricky part is that when the region master goes offline another one needs to take its place, and you can get inconsistency or unavailability depending on how it is set up.

I’d like to see a deep dive of how foundationdb handles this. It has to trade-off consistency for availability at some point and it would be nice to know exactly where.