Introduction
In my last article, I wrote about Paxos (What is Paxos?). Paxos could only determine a single value. Nothing more, nothing less.
SMR and Total Order Broadcast
SMR (State machine replication) is a method of achieving fault-tolerant service by replicating servers and having those servers cooperate. All replicated servers (replicas) have exact copies. This allows for improved availability by allowing a replacement replica to provide service in the event of a failure of one of the replicas.
However, all replicas must apply the operations in the same order to operate to keep the replicas in the same state as each other. To accomplish this, total order broadcast is used. And Multi-Paxos, which we will discuss in this article, is used for all-order broadcasts.
Multi-Paxos
As mentioned above, Multi-Paxos wants to agree on the order of execution of instructions. The figure below shows an illustration of Paxos and Multi-Paxos.
The Paxos figure depicts a single value being determined by all participants. The Multi-Paxos figure depicts a blue replica as the leader, and multiple values are determined by consensus. The leader serializes the execution of each Paxos.
To accomplish this, include the proposal number used by Paxos and the i in the index number of the i-th order in the message to be transacted in each request.
Comment
Leader changes and other detailed specifications are in this paper.
Thanks for reading to the end!
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