Comparing Proof of Authority consensus protocols
Besu implements the Clique, IBFT 2.0, and QBFT Proof of Authority consensus protocols. Proof of Authority consensus protocols work when participants know each other and there is a level of trust between them. For example, in a permissioned consortium network.
Proof of Authority consensus protocols have faster block times and a much greater transaction throughput than the Ethash Proof of Work consensus protocol used on the Ethereum MainNet.
In Clique, IBFT 2.0, or QBFT, a group of nodes in the network act as signers (Clique) or validators (IBFT 2.0 and QBFT). The existing nodes in the signer/validator pool vote to add nodes to or remove nodes from the pool.
For the rest of this page, the term validator is used to refer to signers and validators.
Properties to consider when comparing Clique, IBFT 2.0, and QBFT are:
- Immediate finality
- Minimum number of validators
IBFT 2.0 and QBFT have immediate finality; there are no forks and all valid blocks get included in the main chain.
Clique does not have immediate finality. Implementations using Clique must be aware of forks and chain reorganizations occurring.
Minimum number of validators
To be Byzantine fault tolerant, IBFT 2.0 and QBFT require a minimum of four validators.
Clique can operate with a single validator but operating with a single validator offers no redundancy if the validator fails.
Byzantine fault tolerant is the ability to function correctly and reach consensus despite nodes failing or propagating incorrect information to peers.
Clique is more fault tolerant than IBFT 2.0 and QBFT. Clique tolerates up to half of the validators failing. IBFT 2.0 and QBFT networks require greater than or equal to two-thirds of validators to be operating to create blocks. For example, an IBFT 2.0 or QBFT network of:
- Four to five validators tolerates one unresponsive validator
- Six to eight validators tolerates two unresponsive validators.
Networks with three or less validators can produce blocks but do not guarantee finality when operating in adversarial environments.
Using IBFT 2.0 or QBFT networks with three nodes for production purposes is not recommended.
Reaching consensus and adding blocks is faster in Clique networks. For Clique, the probability of a fork increases as the number of validators increases.
For IBFT 2.0 and QBFT, the time to add new blocks increases as the number of validators increases.