Chained replicas

Current implementation of read-only replicas require them to be connected to the cluster. It means that every new replica adds some overhead to the operational cluster nodes, particularly its leader. It creates limitation of the feature as one might want to add more replicas for better data distribution and scaling out reads, but it is limited to how many replicas the leader can deal with without degrading transactional performance.

Chained replicas would allow connecting a replica node to another replica node. For example, there could be two "primary" replicas and four additional replicas, so reads and subscriptions can be done on six replicas where only two of them are connected to the source cluster.

It would also help for disaster recovery scenarios where three replicas can be promoted to a cluster but only one or two will replicate from the cluster.