Merge pull request #4 from caipengbo/sentinel-7.2

Read sentinel code

src/sentinel.c

@@ -156,6 +156,7 @@ typedef struct instanceLink {
     int refcount;          /* Number of sentinelRedisInstance owners. */
     int disconnected;      /* Non-zero if we need to reconnect cc or pc. */
     int pending_commands;  /* Number of commands sent waiting for a reply. */
+    // 建立两个异步连接
     redisAsyncContext *cc; /* Hiredis context for commands. */
     redisAsyncContext *pc; /* Hiredis context for Pub / Sub. */
     mstime_t cc_conn_time; /* cc connection time. */
@@ -251,7 +252,7 @@ typedef struct sentinelRedisInstance {
     sds info; /* cached INFO output */
 } sentinelRedisInstance;
 
-/* Main state. */
+/* Main state. 全局变量 */
 struct sentinelState {
     char myid[CONFIG_RUN_ID_SIZE+1]; /* This sentinel ID. */
     uint64_t current_epoch;         /* Current epoch. */
@@ -2419,7 +2420,7 @@ void sentinelReconnectInstance(sentinelRedisInstance *ri) {
                 ri->addr = tryResolveAddr;
             }
         }
-
+        // 建立异步连接
         link->cc = redisAsyncConnectBind(ri->addr->ip,ri->addr->port,server.bind_source_addr);
 
         if (link->cc && !link->cc->err) anetCloexec(link->cc->c.fd);
@@ -2680,7 +2681,7 @@ void sentinelRefreshInstanceInfo(sentinelRedisInstance *ri, const char *info) {
             (ri->master->flags & SRI_FAILOVER_IN_PROGRESS) &&
             (ri->master->failover_state ==
                 SENTINEL_FAILOVER_STATE_WAIT_PROMOTION))
-        {
+        {  // 这个地方是发送 slaveof no one 后，通过 INFO 检查到变成主了
             /* Now that we are sure the slave was reconfigured as a master
              * set the master configuration epoch to the epoch we won the
              * election to perform this failover. This will force the other
@@ -3159,6 +3160,7 @@ void sentinelSendPeriodicCommands(sentinelRedisInstance *ri) {
         (ri->info_refresh == 0 ||
         (now - ri->info_refresh) > info_period))
     {
+        // 异步发送 info 命令
         retval = redisAsyncCommand(ri->link->cc,
             sentinelInfoReplyCallback, ri, "%s",
             sentinelInstanceMapCommand(ri,"INFO"));
@@ -4601,6 +4603,7 @@ void sentinelReceiveIsMasterDownReply(redisAsyncContext *c, void *reply, void *p
     }
 }
 
+// 向监控该 master 的其他 Sentinel 发送 SENTINEL IS-MASTER-DOWN-BY-ADDR 命令，该函数中没有 check response
 /* If we think the master is down, we start sending
  * SENTINEL IS-MASTER-DOWN-BY-ADDR requests to other sentinels
  * in order to get the replies that allow to reach the quorum
@@ -4610,6 +4613,7 @@ void sentinelAskMasterStateToOtherSentinels(sentinelRedisInstance *master, int f
     dictIterator *di;
     dictEntry *de;
 
+    // 遍历监控这个 master 上面的其他的 Sentinel
     di = dictGetIterator(master->sentinels);
     while((de = dictNext(di)) != NULL) {
         sentinelRedisInstance *ri = dictGetVal(de);
@@ -4720,6 +4724,7 @@ int sentinelLeaderIncr(dict *counters, char *runid) {
  * To be a leader for a given epoch, we should have the majority of
  * the Sentinels we know (ever seen since the last SENTINEL RESET) that
  * reported the same instance as leader for the same epoch. */
+// 因为已经询问了其他 sentinel 的 Leader, 查看每个 Sentinel 的 leader runid, 统计自己是否是leader
 char *sentinelGetLeader(sentinelRedisInstance *master, uint64_t epoch) {
     dict *counters;
     dictIterator *di;
@@ -4912,7 +4917,7 @@ int sentinelStartFailoverIfNeeded(sentinelRedisInstance *master) {
         }
         return 0;
     }
-
+    // 设置 failover 状态机开始
     sentinelStartFailover(master);
     return 1;
 }
@@ -5051,6 +5056,7 @@ void sentinelFailoverWaitStart(sentinelRedisInstance *ri) {
     sentinelEvent(LL_WARNING,"+elected-leader",ri,"%@");
     if (sentinel.simfailure_flags & SENTINEL_SIMFAILURE_CRASH_AFTER_ELECTION)
         sentinelSimFailureCrash();
+    // 对于 Leader 才继续执行状态机，将状态设置为 SENTINEL_FAILOVER_STATE_SELECT_SLAVE
     ri->failover_state = SENTINEL_FAILOVER_STATE_SELECT_SLAVE;
     ri->failover_state_change_time = mstime();
     sentinelEvent(LL_WARNING,"+failover-state-select-slave",ri,"%@");
@@ -5246,6 +5252,7 @@ void sentinelFailoverSwitchToPromotedSlave(sentinelRedisInstance *master) {
     sentinelResetMasterAndChangeAddress(master,ref->addr->hostname,ref->addr->port);
 }
 
+// failover 状态机
 void sentinelFailoverStateMachine(sentinelRedisInstance *ri) {
     serverAssert(ri->flags & SRI_MASTER);
 
@@ -5255,13 +5262,16 @@ void sentinelFailoverStateMachine(sentinelRedisInstance *ri) {
         case SENTINEL_FAILOVER_STATE_WAIT_START:
             sentinelFailoverWaitStart(ri);
             break;
-        case SENTINEL_FAILOVER_STATE_SELECT_SLAVE:
+        case SENTINEL_FAILOVER_STATE_SELECT_SLAVE:  // leader sentinel 才会走到这个状态
+            // 选择新主
             sentinelFailoverSelectSlave(ri);
             break;
         case SENTINEL_FAILOVER_STATE_SEND_SLAVEOF_NOONE:
+            // 发送 slaveof no one 给新主
             sentinelFailoverSendSlaveOfNoOne(ri);
             break;
         case SENTINEL_FAILOVER_STATE_WAIT_PROMOTION:
+            // 这个函数只检查 timeout，真正检查是否成为主的逻辑在 INFO 的解析中（sentinelRefreshInstanceInfo）
             sentinelFailoverWaitPromotion(ri);
             break;
         case SENTINEL_FAILOVER_STATE_RECONF_SLAVES:
@@ -5298,6 +5308,7 @@ void sentinelHandleRedisInstance(sentinelRedisInstance *ri) {
     /* ========== MONITORING HALF ============ */
     /* Every kind of instance */
     sentinelReconnectInstance(ri);
+    // 周期性的发送探测命令
     sentinelSendPeriodicCommands(ri);
 
     /* ============== ACTING HALF ============= */
@@ -5320,9 +5331,11 @@ void sentinelHandleRedisInstance(sentinelRedisInstance *ri) {
 
     /* Only masters */
     if (ri->flags & SRI_MASTER) {
+        // 判断客观下线
         sentinelCheckObjectivelyDown(ri);
         if (sentinelStartFailoverIfNeeded(ri))
             sentinelAskMasterStateToOtherSentinels(ri,SENTINEL_ASK_FORCED);
+        // 开启状态机
         sentinelFailoverStateMachine(ri);
         sentinelAskMasterStateToOtherSentinels(ri,SENTINEL_NO_FLAGS);
     }