GHOST-based Recursive ANcestor Deriving Prefix Agreement

Designed for efficiency and flexibility, GRANDPA is an asynchronous consensus layer for finality that allows for granular control over finality structure while being able to handle network partitions without degrading consistency. With GHOST (Greedy Heaviest Observed Subtree) as the module for navigating fork choices, the network can guarantee consolidation on a single historic state.

What is Finality

Finality is the property providing guarantees that a transaction (or group of transactions) has become irreversible. Finality can either be absolute or probabilistic. Absolute finality is technologically secured (deterministic), and probabilistic finality is economically secured.

In POW systems, such as Bitcoin, finality is probabilistic, meaning that a transaction is never truly considered irreversible; block reorgs or rollbacks can theoretically happen at any time and any depth; therefore, in probabilistic environments, finality is established based on the economic weight of transactions on top of it. Here, parties assume that new incoming blocks of transactions will consume resources as time passes. At some point, the economic cost of those resources is sufficient enough that an attacker will not be interested in reverting beyond the original transaction's block.

On the other end of the spectrum are POS systems that predominantly leverage absolute finality. Here, finality becomes a parameter hard-coded into the consensus processes; once a specific threshold is met (this could be transaction volume, block progress, or any other arbitrary metric such as time), the system begins using that version of the state as its reference point; meaning in the event a transaction comes in that does not align with the most recent finalized state or a validators attempts to push an alternative history set, the system will not accept it.

Finality in ATLETA

Due to the liveness guarantees, asynchronous voter substitution, deadlock freeness and robust fallback mechanism, ATLETA will leverage GRANDPA or GHOST-based Recursive ANcestor Deriving Prefix Agreement as its finality gadget.

Initially, ATLETA will be implementing immediate, per-block finality. While this decision is superior from the standpoint of security (minimizing MEV surface area) it comes at the cost of performance and disincentivization of independent validator operators. In the future, it is not impossible to assume that the operational demands change and the governing community decides to adjust this. By opting for GRANDPA, it will be possible to adjust the finality parameter ad hoc.

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