Currently, each sstable has data for all the ranges that node is handling. If we change that and rather have separate sstables for each range that node is handling, it can lead to some improvements.
1) Node rebuild will be very fast as sstables can be directly copied over to the bootstrapping node. It will minimize any application level logic. We can directly use Linux native methods to transfer sstables without using CPU and putting less pressure on the serving node. I think in theory it will be the fastest way to transfer data.
2) Backup can only transfer sstables for a node which belong to its primary keyrange.
3) ETL process can only copy one replica of data and will be much faster.
We can split the writes into multiple memtables for each range it is handling. The sstables being flushed from these can have details of which range of data it is handling.
There will be no change I think for any reads as they work with interleaved data anyway. But may be we can improve there as well?
The change does not look very complicated. I am not taking into account how it will work when ranges are being changed for nodes.
Vnodes might make this work more complicated. We can also have a bit on each sstable which says whether it is primary data or not.