My understanding is the PendingRangeCalculator is meant to calculate who should receive extra writes during range movements. However, it adds the wrong ranges for moves. An extreme example of this can be seen in the following reproduction. Create a 5 node cluster (I did this on 2.0.16 and 2.2.4) and a keyspace RF=3 and a simple table. Then start moving a node and immediately kill -9 it. Now you see a node as down and moving in the ring. Try a quorum write for a partition that is stored on that node - it will fail with a timeout. Further, all CAS reads or writes fail immediately with unavailable exception because they attempt to include the moving node twice. This is likely to be the cause of
In my example I had this ring:
127.0.0.1 rack1 Up Normal 170.97 KB 20.00% -9223372036854775808
127.0.0.2 rack1 Up Normal 124.06 KB 20.00% -5534023222112865485
127.0.0.3 rack1 Down Moving 108.7 KB 40.00% 1844674407370955160
127.0.0.4 rack1 Up Normal 142.58 KB 0.00% 1844674407370955161
127.0.0.5 rack1 Up Normal 118.64 KB 20.00% 5534023222112865484
Node 3 was moving to -1844674407370955160. I added logging to print the pending and natural endpoints. For ranges owned by node 3, node 3 appeared in pending and natural endpoints. The blockFor is increased to 3 so we’re effectively doing CL.ALL operations. This manifests as write timeouts and CAS unavailables when the node is down.
The correct pending range for this scenario is node 1 is gaining the range (-1844674407370955160, 1844674407370955160). So node 1 should be added as a destination for writes and CAS for this range, not node 3.