Liveness

A guarantee that a system will continue to provide data, and that no centralized authority can shut down its services.

What Is Liveness?

A rise in cryptocurrencies prompted the creation of consensus algorithms. For distributed systems, liveness means that a protocol is able to exchange messages among nodes, with the nodes successfully coming to a consensus. 

This means that a system has liveness guaranteed.

Blockchains are regularly trying to determine which history of transactions is accurate, rather than the messages itself. 

Distributed systems have a degree of correctness, and this involves an ordering of transactions. There are two elements involved in this — liveness and safety. 

Liveness guarantees that good things will happen eventually, meaning there is no timeframe for these things to happen. 

Termination of a distributed computation is one of many examples of liveness. 

Liveness is the guarantee that all validators will reach some consensus on a value. 

This can be thought of as the guarantee that no two validators will be in disagreement and reach different values. ‍

Conversely, safety is a guarantee that nothing bad will happen. 

For example, Bitcoin’s use of the Nakamoto Consensus means that there is an emphasis on liveness on Bitcoin’s blockchain. Nakamoto Consensus uses Proof-of-Work mining along with a metric called “longest chain wins” to determine which history is accurate. 

The history and the expected history will be the same if nodes were honest. 

A node which is a copy of the ledger operated by a participant of the blockchain network should not show different values when compared to another node. 

Two nodes yielding different values represents a problem. 

Nodes must reach agreement on what the next block should include.