Raft 论文摘要（二）

several goals in designing Raft:

• it must providea complete and practical foundation for system building;

• it must be safe under all conditions and available under typical operating conditions;

• it must be efficient for common operations.

Our most important goal — and most difficult challenge — was understandability.

There were numerous points in the design of Raft where we had to choose among alternative approaches. In these situations we evaluated the alternatives based on understandability.

We used two techniquesthat are generally applicable:

• The first technique is the well-known approach of problem decomposition: wherever possible, we divided problems into separate pieces that could be solved, explained, and understood relatively independently.

• Our second approach was to simplify the state spaceby reducing the number of states to consider, making the system more coherent and eliminating nondeterminism where possible.

We used randomization to simplify the Raft leader election algorithm.

Raft implements consensus by first electing a distinguished leader, then giving the leader complete responsibility for managing the replicated log.

Raft decomposes the consensus problem into three relatively independent subproblems:

• Leader election: a new leader must be chosen when an existing leader fails;

• Log replication: the leader must accept log entries from clients and replicate them across the cluster, forcing the other logs to agree with its own;

• Safety: the key safety property for Raft is the State Machine Safety Property in Figure 3: if any serverhas applied a particular log entry to its state machine,then no other server may apply a different commandfor the same log index.