Aptos

Aptos is the successor to the Diem blockchain project (formerly known as Libra), which Meta iscontinued in early 2022. Aptos uses a Proof-ofStake (PoS) consensus mechanism, DiemBFTv4, for global consensus. In this regard, Aptos is most similar to Tendermint and can be thought of as an evolution of leader-based PBFT protocols. However, Aptos distinguishes itself by enabling parallel execution through its Block-STM. In Aptos, validators group transactions into batches. When a client submits a transaction, it is broadcast to all validators, each of which independently processes the transaction and adds it to their batch. These compiled and signed block batches are then sent to all other validators, who store them persistently. This “continuous transaction dissemination”, as the name suggests, happens continuously between all network validators. These persistent block stores, or “mempools”, serve as batch storage. Transactions are validated locally when the majority of stake-weighted signatures (one-half plus one) from other validators are received. A leader is temporarily selected from the active validator set via the DiemBFTv4 protocol. The leader’s role is to order their block batches and propose a new block, a process known as “block metadata ordering,” which closely mirrors Tendermint’s voting mechanism. Batch metadata ordering undergoes two rounds of voting, where two-thirds plus one of the validators must agree. Once the block metadata are agreed upon, each validator can independently execute the block batches on their ledger. Periodically, the validators share their ledger status with other validators, ensuring that a globally authenticated ledger propagates throughout the network. Unlike Sui or GTBS, which prioritize horizontal scalability through alternative means, Aptos aims to achieve scalability primarily through network sharding. This approach, similar to those used by Ten8 dermint derivatives, divides the network into multiple states to improve throughput. However, sharding introduces additional complexity and can negatively impact the network’s liveness–the property that ensures that the network can continue functioning over time.