The objective of all blockchain protocols is to replicate a blockchain and its associated state across participating nodes. To achieve such an agreement, each blockchain protocol deploys a consensus algorithm.
The public Aergo network uses Delegated Proof of Stake (DPoS) for blockchain consensus.
- BP Election
In DPoS, blocks are generated only by a limited number of nodes called Block Producers (BPs). BPs are elected via voting, where the voting power is weighted by staked tokens.
BPs are re-elected round by round (blocks per round = the total number of the BPs). In each round, time is split into slots and each slot is assigned to one of the elected BPs. Only the permitted BP can produce a block in a time slot.
- Staking & Voting
Staking means locking up one’s tokens for a minimum period of time. Any user wanting to vote must stake their tokens since the voting power is weighted by the number of staked tokens, as remarked above.
Voting is performed via a transaction. Voting results do not come into effect immediately. The current BPs are elected based on the voting result gathered at the block number: (<current block number> / <the total number of BPs> - 1) * <the total number of BPs>.
In other words, the voting results gathered in the past (approximately 1 round before) are used for stability (recent blocks may be roll-backed via a reorganization).
Votes are locked for a certain period of time to prevent users from spamming votes. On the public Aergo network, this is currently approx. 1 day. That means, after casting a vote, a user can only change their vote after 1 day has passed.
- Last Irreversible Block (LIB)
In some blockchain protocols, a blockchain may branch into two or more, which is called a fork. Later, only one of them is chosen as the main branch via a set of rules defined by the protocol. Such reorganizations limit each block’s finality and, in turn, transaction’s finality. For example, a transaction, included in a block at one time, might be rejected later.
DPoS also allows blockchain forks. However, a block becomes a last irreversible block (LIB) when it is (double time) confirmed by a majority (2/3+) of BPs. Once a block is determined as a LIB, it cannot be rolled back, i.e. it achieves finality.