Replication attestation

How to ensure a minimum of confirmation from the storage nodes to ensure the data availability of a given transaction. If we are not providing this kind of mechanism, we can end up into a network split / mismatch where shards and beacon aren't cross linked. Also we do not want to overload the beacon chain by broadcasting it with hundred of messages for a single transaction summary.

Heuristic solution

Each validation node will notify the replications nodes in charge, and wait their confirmations to attest the validity and the availability of the transaction in the shard before notifying the beacon chain and the welcome node.

In 1st approx, a single notification from the validation nodes is sufficient to ensure the availability. This attestation will contain a list of signatures, from the replication nodes, to status about their commitment to store the transaction. However, further attestations and confirmations can be checked later during the time, to provide more security.

For example, a beacon chain receiving 1 attestation from a validation node including X storage confirmations will be valid as 3 attestations with their respective confirmations.

Nested replications

Moreover, when we are dealing with recipients for transfer or smart contract calls, we want to support the recipients shards will be notified only when the main transaction is validated and stored. So for example, the replication can be splitted by levels: [ Main Chain ] -> [ Recipient Chains]

Then the welcome node will be notified by a validation node with a given number of replica confirmations.

          V1
        /  |  \
Chain: S1  S2  S3
       /     |   \
      Recipient Shards

Client notifications

When a transaction is submitted, the welcome node will transfer this transaction to the validation nodes and return a pending status to the client. The client would have to subscribe to notifications about the completion of the transaction. Once the transaction will be validated and the validation nodes by notifing the welcome will notify the clients asynchronously.

Further improvements

To reduce the overall size of the attestations and confirmations we can support signature aggregation or cosigning to embed a single transaction with a bitfield to indicate which nodes signed the transaction replication, which will be signed over by a validation node.