2021-06-29 redis-cluster集群failover的处理

摘要:

在paxos和raft一致性协议中, 选举是分多轮次进行。但是在具体项目实践中，需要谨慎处理各种细节。

本文记录redis的设计和实现

核心代码：

/* This function is called if we are a slave node and our master serving
 * a non-zero amount of hash slots is in FAIL state.
 *
 * The gaol of this function is:
 * 1) To check if we are able to perform a failover, is our data updated?
 * 2) Try to get elected by masters.
 * 3) Perform the failover informing all the other nodes.
 */
void clusterHandleSlaveFailover(void) {
    mstime_t data_age;
    mstime_t auth_age = mstime() - server.cluster->failover_auth_time;
    int needed_quorum = (server.cluster->size / 2) + 1;
    int manual_failover = server.cluster->mf_end != 0 &&
                          server.cluster->mf_can_start;
    mstime_t auth_timeout, auth_retry_time;

    server.cluster->todo_before_sleep &= ~CLUSTER_TODO_HANDLE_FAILOVER;

    /* Compute the fail