Rebalance effect on bucket types
The rebalance operation works across the cluster both on the Couchbase and memcached buckets.
There are differences in the rebalance operation for the Couchbase and memcached buckets due to the inherent differences of the two bucket types.
For Couchbase buckets:
- Data is rebalanced across all nodes in the cluster to match the new configuration.
- The 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 added to the cluster, each new node is added to the cluster and to the list of nodes supporting the memcached bucket data.
- If nodes are removed from the cluster, the data stored on that node within the memcached bucket is lost and the node is 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. However, server node changes can shift the hashing and invalidate some keys once the rebalance operation is completed.