Redis におけるクラスターのマスター/スレーブ レプリケーションの原理の簡単な分析

./redis-server --replicaof masterip masterport

slaveof masterip masterport

slaveof no one

//每1s执行这个方法
void replicationCron(void) {
    ...
    //检查是否需要连接到master 如果是REPL_STATE_CONNECT状态，必须连接到master
    //#define REPL_STATE_CONNECT 1  Must connect to master 
    if (server.repl_state == REPL_STATE_CONNECT) {
        serverLog(LL_NOTICE,"Connecting to MASTER %s:%d",
            server.masterhost, server.masterport);
        //和master创建连接    
        if (connectWithMaster() == C_OK) {
            serverLog(LL_NOTICE,"MASTER <-> REPLICA sync started");
        }
    }
    
    //发送ping命令给slave 
    if ((replication_cron_loops % server.repl_ping_slave_period) == 0 &&
        listLength(server.slaves))
    {
        /* Note that we don&#39;t send the PING if the clients are paused during
         * a Redis Cluster manual failover: the PING we send will otherwise
         * alter the replication offsets of master and slave, and will no longer
         * match the one stored into &#39;mf_master_offset&#39; state. */
        int manual_failover_in_progress =
            server.cluster_enabled &&
            server.cluster->mf_end &&
            clientsArePaused();

        if (!manual_failover_in_progress) {
            ping_argv[0] = createStringObject("PING",4);
            replicationFeedSlaves(server.slaves, server.slaveseldb,
                ping_argv, 1);
            decrRefCount(ping_argv[0]);
        }
    }
    
    //发送换行符到所有slave,告诉slave等待接收rdb文件
    listRewind(server.slaves,&li);
    while((ln = listNext(&li))) {
        client *slave = ln->value;

        int is_presync =
            (slave->replstate == SLAVE_STATE_WAIT_BGSAVE_START ||
            (slave->replstate == SLAVE_STATE_WAIT_BGSAVE_END &&
             server.rdb_child_type != RDB_CHILD_TYPE_SOCKET));

        if (is_presync) {
            if (write(slave->fd, "\n", 1) == -1) {
                /* Don&#39;t worry about socket errors, it&#39;s just a ping. */
            }
        }
    }
    ...
}

Replication ID, offset

    //没有在rdb进程，没有aof重写进程
    if (server.rdb_child_pid == -1 && server.aof_child_pid == -1) {
        time_t idle, max_idle = 0;
        int slaves_waiting = 0;
        int mincapa = -1;
        listNode *ln;
        listIter li;

        listRewind(server.slaves,&li);
        while((ln = listNext(&li))) {
            client *slave = ln->value;
            //判断slave是否是等待bgsave状态
            if (slave->replstate == SLAVE_STATE_WAIT_BGSAVE_START) {
            //多久没有发送心跳或查询数据了 空闲时间间隔
                idle = server.unixtime - slave->lastinteraction;
                if (idle > max_idle) max_idle = idle;
                slaves_waiting++;
                mincapa = (mincapa == -1) ? slave->slave_capa :
                                            (mincapa & slave->slave_capa);
            }
        }

        if (slaves_waiting &&
            (!server.repl_diskless_sync ||
             max_idle > server.repl_diskless_sync_delay))
        {
            /* Start the BGSAVE. The called function may start a
             * BGSAVE with socket target or disk target depending on the
             * configuration and slaves capabilities. */
             //bgsave rdb生成
            startBgsaveForReplication(mincapa);
        }
    }