深入淺析Redis中的sentinel故障轉移

./redis-sentinel ../sentinel.conf

./redis-server ../sentinel.conf --sentinel

truct redisCommand redisCommandTable[] = {
    {"module",moduleCommand,-2,"as",0,NULL,0,0,0,0,0},
    {"get",getCommand,2,"rF",0,NULL,1,1,1,0,0},
    {"set",setCommand,-3,"wm",0,NULL,1,1,1,0,0},
    {"setnx",setnxCommand,3,"wmF",0,NULL,1,1,1,0,0},
    {"setex",setexCommand,4,"wm",0,NULL,1,1,1,0,0},
    {"psetex",psetexCommand,4,"wm",0,NULL,1,1,1,0,0},
    {"append",appendCommand,3,"wm",0,NULL,1,1,1,0,0},
    .....
    {"del",delCommand,-2,"w",0,NULL,1,-1,1,0,0},
    {"unlink",unlinkCommand,-2,"wF",0,NULL,1,-1,1,0,0},
    {"exists",existsCommand,-2,"rF",0,NULL,1,-1,1,0,0},
    {"setbit",setbitCommand,4,"wm",0,NULL,1,1,1,0,0},
    {"getbit",getbitCommand,3,"rF",0,NULL,1,1,1,0,0},
    {"bitfield",bitfieldCommand,-2,"wm",0,NULL,1,1,1,0,0},
    {"setrange",setrangeCommand,4,"wm",0,NULL,1,1,1,0,0},
    {"getrange",getrangeCommand,4,"r",0,NULL,1,1,1,0,0},
    {"substr",getrangeCommand,4,"r",0,NULL,1,1,1,0,0},
    {"incr",incrCommand,2,"wmF",0,NULL,1,1,1,0,0},
    {"decr",decrCommand,2,"wmF",0,NULL,1,1,1,0,0},
    {"mget",mgetCommand,-2,"rF",0,NULL,1,-1,1,0,0},
    {"rpush",rpushCommand,-3,"wmF",0,NULL,1,1,1,0,0},
    {"lpush",lpushCommand,-3,"wmF",0,NULL,1,1,1,0,0}
    ......
    }

struct redisCommand sentinelcmds[] = {
    {"ping",pingCommand,1,"",0,NULL,0,0,0,0,0},
    {"sentinel",sentinelCommand,-2,"",0,NULL,0,0,0,0,0},
    {"subscribe",subscribeCommand,-2,"",0,NULL,0,0,0,0,0},
    {"unsubscribe",unsubscribeCommand,-1,"",0,NULL,0,0,0,0,0},
    {"psubscribe",psubscribeCommand,-2,"",0,NULL,0,0,0,0,0},
    {"punsubscribe",punsubscribeCommand,-1,"",0,NULL,0,0,0,0,0},
    {"publish",sentinelPublishCommand,3,"",0,NULL,0,0,0,0,0},
    {"info",sentinelInfoCommand,-1,"",0,NULL,0,0,0,0,0},
    {"role",sentinelRoleCommand,1,"l",0,NULL,0,0,0,0,0},
    {"client",clientCommand,-2,"rs",0,NULL,0,0,0,0,0},
    {"shutdown",shutdownCommand,-1,"",0,NULL,0,0,0,0,0},
    {"auth",authCommand,2,"sltF",0,NULL,0,0,0,0,0}
}

struct sentinelState {
 
    char myid[CONFIG_RUN_ID_SIZE+1]; /* This sentinel ID. */
    
    //当前纪元，用于实现故障转移
    uint64_t current_epoch;         /* Current epoch. */
    
    //监视的主服务器
    //字典的键是主服务器的名字
    //字典的值则是一个指向sentinelRedisInstances结构的指针
    dict *masters;      /* Dictionary of master sentinelRedisInstances.
                           Key is the instance name, value is the
                           sentinelRedisInstance structure pointer. */
    //是否进入tilt模式
    int tilt;           /* Are we in TILT mode? */
    
    //目前正在执行的脚本数量
    int running_scripts;    /* Number of scripts in execution right now. */
    
    //进入tilt模式的时间
    mstime_t tilt_start_time;       /* When TITL started. */
    
    //最后一次执行时间处理器的时间
    mstime_t previous_time;         /* Last time we ran the time handler. */
    
    // 一个FIFO队列，包含了所有需要执行的用户脚本
    list *scripts_queue;            /* Queue of user scripts to execute. */
    
    char *announce_ip;  /* IP addr that is gossiped to other sentinels if
                           not NULL. */
    int announce_port;  /* Port that is gossiped to other sentinels if
                           non zero. */
    unsigned long simfailure_flags; /* Failures simulation. */
    int deny_scripts_reconfig; /* Allow SENTINEL SET ... to change script
                                  paths at runtime? */
}

typedef struct sentinelRedisInstance {
    //标识值，记录了实例的类型，以及该实例的当前状态
    int flags;      /* See SRI_... defines */
    
    //实例的名字
    //主服务器的名字由用户在配置文件中设置
    //从服务器以及Sentinel的名字由Sentinel自动设置
    //格式为ip:port,例如“127.0.0.1:26379”
    char *name;     /* Master name from the point of view of this sentinel. */
    
    //实例运行的ID
    char *runid;    /* Run ID of this instance, or unique ID if is a Sentinel.*/
    
    //配置纪元，用于实现故障转移
    uint64_t config_epoch;  /* Configuration epoch. */
    
    //实例的地址
    sentinelAddr *addr; /* Master host. */
    
    //sentinel down-after-milliseconds选项设定的值
    //实例无响应多少毫秒之后才会被判断为主观下线（subjectively down）
    mstime_t down_after_period; /* Consider it down after that period. */
    
    //sentinel monitor    选项中的quorum
    //判断这个实例为客观下线（objective down）所需的支持投票的数量
    unsigned int quorum;/* Number of sentinels that need to agree on failure. */  
    //sentinel parallel-syncs   选项的numreplicas值
    //在执行故障转移操作时，可以同时对新的主服务器进行同步的从服务器数量
    int parallel_syncs; /* How many slaves to reconfigure at same time. */
    
    //sentinel failover-timeout  选项的值
    //刷新故障迁移状态的最大时限
    mstime_t failover_timeout;      /* Max time to refresh failover state. */
}

# sentinel monitor    
sentinel monitor master1 127.0.0.1 6379 2

# sentinel down-after-milliseconds  
sentinel down-after-milliseconds master1 30000

# sentinel parallel-syncs  
sentinel parallel-syncs master1 1

# sentinel failover-timeout  
sentinel failover-timeout master1 900000

     PUBLISH _sentinel_:hello   ",,,,,,,"

SENTINEL is-master-down-by-addr    

sentinel monitor