When the last owner of a segment leaves the cache, the coordinator will update the consistent hash and replace that owner with numOwners owners (so that a segment always has at least 1 owner). If there is a rebalance in progress, it could be that both the current and the pending CH lost all the owners of a segment, and the coordinator will assign new owners in both CHs (not necessarily the same).

Sometimes, this causes tests that create clusters with many nodes to spend a lot of time shutting down the cluster. Here's an example:

1. Cluster ABCDE, coordinator A, topology id = 0, currentCH = {0: CD, 1: BC}, pendingCH = null
2. D leaves
3. A broadcasts a REBALANCE_START command with topology id 1, members = ABCE, currentCH = {0: C, 1: BC}, pendingCH = {0: BC, 1: BC}
4. A and E confirm that they finished the rebalance
5. C leaves before sending the data for segment 0 to B
6. A broadcasts a CH_UPDATE command with topology id 2, members = ABE, currentCH = {0: AE, 1: B}, pendingCH = {0: B, 1: B}
7. A now owns segment 0 in the writeCH (which is the union of currentCH and pendingCH).
8. A tries to request segment 0 from the other owner in the currentCH, E
9. B confirms that it finished the rebalance
10. A broadcasts a new topology: topology id 3, currentCH = {0: B, 1: B}, pendingCH = null
11. E installs topology 3, and throws an IllegalArgumentException when handling A's request for segments
12. A is not able to install topology 3, because it requests the transactions data while holding the lock on the LocalCacheStatus
13. A receives the IllegalArgumentException from E and retries. But because it still has the old topology, it retries on E ad infinitum - using a lot of CPU in the process.

A requesting segment 0 from E is not a problem in itself - normally E would just send back an empty set of transactions and entries. The problem is that the cluster is able to install a new topology, because A already confirmed receiving all the data, but A is stuck with the old topology.