SMR in Practice Via a Log

By now, we have learned what state machine replication is and how it is implemented to tolerate$t$ faults. This lesson foreshadows the upcoming chapters on Paxos State Machine and Raft State Machine replications, both practical and widely used consensus algorithms. We will see how Paxos and Raft take the SMR ideas and implement them.

Log data structure

Every state machine of the replica group maintains a data structure called a log. We can consider a log as a file that consists of slotA slot can be considered a placeholder for client command or SMR's own internal commands. Each slot can store one command. numbers, starting from the left and extending indefinitely on the right. Often, these slot numbers are sequentially numbered starting ...