This change is related to, but somewhat orthogonal to
Currently all the shard tuples for a given counter cell are packed, in sorted order, in one binary blob. Thus reconciling N counter cells requires allocating a new byte buffer capable of holding the union of the two context's shards N-1 times.
For writes, in post
CASSANDRA-6504 world, it also means reading more data than we have to (the complete context, when all we need is the local node's global shard).
Splitting the context into separate cells, one cell per shard, will help to improve this. We did a similar thing with super columns for
CASSANDRA-3237. Incidentally, doing this split is now possible thanks to CASSANDRA-3237.
Doing this would also simplify counter reconciliation logic. Getting rid of old contexts altogether can be done trivially with upgradesstables.
In fact, we should be able to put the logical clock into the cell's timestamp, and use regular Cell-s and regular Cell reconcile() logic for the shards, especially once we get rid of the local/remote shards some time in the future (until then we still have to differentiate between global/remote/local shards and their priority rules).
|Replace counter cache with optimised counter read path||Open||Unassigned|
|Get rid of pre-2.1 created local and remote counter shards||Open||Unassigned|