The rebalance operation works across the cluster on both
Couchbase and memcached buckets, but there
are differences in the rebalance operation due to the inherent
differences of the two bucket types.
For Couchbase buckets:
Data is rebalance across all the nodes in the cluster to match the new configuration.
Updated vBucket map is communicated to clients as each vBucket is successfully moved.
No data is lost, and there are no changes to the caching or availability of individual keys.
For memcached buckets:
If new nodes are being added to the cluster, the new node is added to the cluster, and the node is added to the list of nodes supporting the memcached bucket data.
If nodes are being removed from the cluster, the data stored on that node within the memcached bucket will be lost, and the node removed from the available list of nodes.
In either case, the list of nodes handling the bucket data is automatically updated and communicated to the client nodes. Memcached buckets use the Ketama hashing algorithm which is designed to cope with server changes, but the change of server nodes may shift the hashing and invalidate some keys once the rebalance operation has completed.