The consensus protocol is the way, for different components of a distributed system, to achieve an agreement about a shared data value. A transaction environment is used by the transaction manager to establish whether a transaction can be committed or aborted, using the following three conditions:

• Agreement: All nodes decide on the same value
• Validity: If all of the nodes have the same value, then a consensus must be obtained on this value
• Termination: All nodes decide about a transaction's outcome

In enterprise architectures, there are three major consensus protocols, as follows:

• Two-phase commit (2PC) protocol
• Three-phase commit (3PC) protocol
• Paxos