Redis源码分析--Sentinel(4)实例处理的Acting half
作者:互联网
Acting half:
一、进入故障转移状态之前:
void sentinelHandleRedisInstance(sentinelRedisInstance *ri) {
// ...
// ...
/* ============== ACTING HALF ============= */
/* We don't proceed with the acting half if we are in TILT mode.
* TILT happens when we find something odd with the time, like a
* sudden change in the clock. */
if (sentinel.tilt) {
if (mstime()-sentinel.tilt_start_time < SENTINEL_TILT_PERIOD) return;
/* 如果30秒内一切正常,退出Tilt模式 */
sentinel.tilt = 0;
sentinelEvent(REDIS_WARNING,"-tilt",NULL,"#tilt mode exited");
}
/* Every kind of instance */
sentinelCheckSubjectivelyDown(ri);
/* Masters and slaves */
if (ri->flags & (SRI_MASTER|SRI_SLAVE)) {
/* Nothing so far. */
}
/* Only masters */
if (ri->flags & SRI_MASTER) {
/* 由于消息的收发都是异步的,所以这里不一定可以直接判断出结果,
* 所以本sentinel会在一次次定时器调用中判断是否需要客观下线 */
sentinelCheckObjectivelyDown(ri);
/* 判断是否进行故障转移,如果进行故障转移,master->failover_state的变化将触发一次命令的发送
* 即本机sentinel要求其他sentinel选举本机为leader*/
if (sentinelStartFailoverIfNeeded(ri))
/* 这里的调用是本机要求选举自己做领头Sentinel,这里只会触发一次 */
sentinelAskMasterStateToOtherSentinels(ri,SENTINEL_ASK_FORCED);
sentinelFailoverStateMachine(ri);
/* 这里发送的消息应该不固定,可能是询问客观下线状态,
* 也可能是要求选举(如果初始选举没有产生leader,
* 这一行会不断触发,直至产生leader) */
sentinelAskMasterStateToOtherSentinels(ri,SENTINEL_NO_FLAGS);
}
}
- L16:检测主观下线状态;
- L27:检测客观下线状态,注意 L24: Only masters;
- L32、L37: 第二节分析 sentinelAskMasterStateToOtherSentinels;
- L30:第三节分析进入故障转移阶段的条件;
- L33:进入故障转移阶段,下一篇文章分析故障转移状态机;
二、发送命令 sentinelAskMasterStateToOtherSentinels:
这个函数很特殊,所以专门用一节讲它。首先先说明这个函数会发送命令:
SENTINEL IS-MASTER-DOWN-BY-ADDR <ip> <port> <current_epoch> <runid>
而根据runid参数不同,会执行两个不同功能:
- 第一个功能:runid为'*'。本机sentinel认为当前master已主观下线,需要询问其他sentinels是否认为该master下线(可能主观,也可能客观,因为不同Sentinel判定标准不同 //todo分析);
- 第二个功能:runid为本机sentinel的runid。本机sentinel已经认定当前master客观下线,要求其他sentinels选举自己为领头Sentinel;
void sentinelAskMasterStateToOtherSentinels(sentinelRedisInstance *master, int flags) {
dictIterator *di;
dictEntry *de;
di = dictGetIterator(master->sentinels);
while((de = dictNext(di)) != NULL) {
sentinelRedisInstance *ri = dictGetVal(de);
mstime_t elapsed = mstime() - ri->last_master_down_reply_time;
char port[32];
int retval;
/* If the master state from other sentinel is too old, we clear it. */
if (elapsed > SENTINEL_ASK_PERIOD*5) {
ri->flags &= ~SRI_MASTER_DOWN;
sdsfree(ri->leader);
ri->leader = NULL;
}
/* Only ask if master is down to other sentinels if:
*
* 1) We believe it is down, or there is a failover in progress.
* 2) Sentinel is connected.
* 3) We did not received the info within SENTINEL_ASK_PERIOD ms. */
if ((master->flags & SRI_S_DOWN) == 0) continue;
if (ri->flags & SRI_DISCONNECTED) continue;
if (!(flags & SENTINEL_ASK_FORCED) &&
mstime() - ri->last_master_down_reply_time < SENTINEL_ASK_PERIOD)
continue;
/* Ask */
ll2string(port,sizeof(port),master->addr->port);
retval = redisAsyncCommand(ri->cc,
/**/
sentinelReceiveIsMasterDownReply, NULL,
"SENTINEL is-master-down-by-addr %s %s %llu %s",
master->addr->ip, port,
sentinel.current_epoch,
/* 根据master当前failover_state判断这是sentinel在进行判断是否客观下线还是要选举该sentinel为leader */
(master->failover_state > SENTINEL_FAILOVER_STATE_NONE) ?
server.runid : "*");
if (retval == REDIS_OK) ri->pending_commands++;
}
dictReleaseIterator(di);
}
-
看一下官方注释
If we think the master is down, we start sending SENTINEL IS-MASTER-DOWN-BY-ADDR requests(1) to other sentinels in order to get the replies(2) that allow to reach the quorum needed to mark(3) the master in ODOWN state and trigger(4) a failover
-
(1):该函数第一个功能;
- (2):L34: 回调函数sentinelReceiveIsMasterDownReply接收回复,根据回复会设置ri->flags & SRI_MASTER_DOWN;
- (3):ri->flags & SRI_MASTER_DOWN会在sentinelCheckObjectivelyDown函数中使quorum++;
- (4):如果客观下线要求达到,那么第一节的sentinelStartFailoverIfNeeded会进入故障转移阶段,即trigger a failover;
-
L34:第三节分析发送SENTINEL is-master-down-by-addr命令的回调函数sentinelReceiveIsMasterDownReply;
三、进入故障转移的条件:
int sentinelStartFailoverIfNeeded(sentinelRedisInstance *master) {
/* We can't failover if the master is not in O_DOWN state. */
if (!(master->flags & SRI_O_DOWN)) return 0;
/* Failover already in progress? */
if (master->flags & SRI_FAILOVER_IN_PROGRESS) return 0;
/* Last failover attempt started too little time ago? */
if (mstime() - master->failover_start_time <
master->failover_timeout*2) return 0;
/* 进行故障转移 */
sentinelStartFailover(master);
return 1;
}
- L3:主服务器必须已经被判定客观下线才会进入故障转移;
- L6:主服务器不能已经在故障转移状态中;
- L12: 进行故障转移,下面继续分析源码:
void sentinelStartFailover(sentinelRedisInstance *master) {
redisAssert(master->flags & SRI_MASTER);
/* 设置FAILOVER_STATE_WAIT_START状态,该状态会在
* sentinelAskMasterStateToOtherSentinels 方法中
* 允许本sentinel要求其他Sentinel选举自己为leader */
master->failover_state = SENTINEL_FAILOVER_STATE_WAIT_START;
master->flags |= SRI_FAILOVER_IN_PROGRESS;
/* 回合数++ */
master->failover_epoch = ++sentinel.current_epoch;
sentinelEvent(REDIS_WARNING,"+new-epoch",master,"%llu",
(unsigned long long) sentinel.current_epoch);
sentinelEvent(REDIS_WARNING,"+try-failover",master,"%@");
/* 维护time信息 */
master->failover_start_time = mstime();
master->failover_state_change_time = mstime();
}
-
L6、L7:master的failover_state和flags都被更新,HandleInstance程序下一次进入故障转移状态机函数时,逻辑才进入故障转移;
-
L9:回合数++,可能不是第一个回合;
标签:--,failover,Redis,SENTINEL,源码,master,sentinel,flags,ri 来源: https://www.cnblogs.com/macguz/p/15865715.html