【MongoDB】复制集主从切换

1.关闭主库。

shard1:PRIMARY> use admin 
switched to db admin
shard1:PRIMARY> db.shutdownServer()
server should be down...
2024-06-15T17:45:12.844+0800 I NETWORK  [js] trying reconnect to 127.0.0.1:27025 failed
2024-06-15T17:45:13.389+0800 I NETWORK  [js] reconnect 127.0.0.1:27025 failed failed 
2024-06-15T17:45:13.391+0800 I NETWORK  [js] trying reconnect to 127.0.0.1:27025 failed
2024-06-15T17:45:13.391+0800 I NETWORK  [js] reconnect 127.0.0.1:27025 failed failed 
> 

2.检查集群状态 

shard1:PRIMARY> rs.status()
{
	"set" : "shard1",
	"date" : ISODate("2024-06-15T09:45:44.129Z"),
	"myState" : 1,
	"term" : NumberLong(3),
	"syncingTo" : "",
	"syncSourceHost" : "",
	"syncSourceId" : -1,
	"heartbeatIntervalMillis" : NumberLong(2000),
	"optimes" : {
		"lastCommittedOpTime" : {
			"ts" : Timestamp(1718444703, 1),
			"t" : NumberLong(2)
		},
		"readConcernMajorityOpTime" : {
			"ts" : Timestamp(1718444703, 1),
			"t" : NumberLong(2)
		},
		"appliedOpTime" : {
			"ts" : Timestamp(1718444734, 1),
			"t" : NumberLong(3)
		},
		"durableOpTime" : {
			"ts" : Timestamp(1718444734, 1),
			"t" : NumberLong(3)
		}
	},
	"lastStableCheckpointTimestamp" : Timestamp(1718444693, 1),
	"members" : [
		{
			"_id" : 0,
			"name" : "192.168.1.51:27023",
			"health" : 1,
			"state" : 1,
			"stateStr" : "PRIMARY",
			"uptime" : 43025,
			"optime" : {
				"ts" : Timestamp(1718444734, 1),
				"t" : NumberLong(3)
			},
			"optimeDate" : ISODate("2024-06-15T09:45:34Z"),
			"syncingTo" : "",
			"syncSourceHost" : "",
			"syncSourceId" : -1,
			"infoMessage" : "",
			"electionTime" : Timestamp(1718444712, 1),
			"electionDate" : ISODate("2024-06-15T09:45:12Z"),
			"configVersion" : 7,
			"self" : true,
			"lastHeartbeatMessage" : ""
		},
		{
			"_id" : 1,
			"name" : "192.168.1.51:27024",
			"health" : 1,
			"state" : 7,
			"stateStr" : "ARBITER",
			"uptime" : 42606,
			"lastHeartbeat" : ISODate("2024-06-15T09:45:42.856Z"),
			"lastHeartbeatRecv" : ISODate("2024-06-15T09:45:42.410Z"),
			"pingMs" : NumberLong(0),
			"lastHeartbeatMessage" : "",
			"syncingTo" : "",
			"syncSourceHost" : "",
			"syncSourceId" : -1,
			"infoMessage" : "",
			"configVersion" : 7
		},
		{
			"_id" : 2,
			"name" : "192.168.1.51:27025",
			"health" : 0,
			"state" : 8,
			"stateStr" : "(not reachable/healthy)",
			"uptime" : 0,
			"optime" : {
				"ts" : Timestamp(0, 0),
				"t" : NumberLong(-1)
			},
			"optimeDurable" : {
				"ts" : Timestamp(0, 0),
				"t" : NumberLong(-1)
			},
			"optimeDate" : ISODate("1970-01-01T00:00:00Z"),
			"optimeDurableDate" : ISODate("1970-01-01T00:00:00Z"),
			"lastHeartbeat" : ISODate("2024-06-15T09:45:42.871Z"),
			"lastHeartbeatRecv" : ISODate("2024-06-15T09:45:12.371Z"),
			"pingMs" : NumberLong(0),
			"lastHeartbeatMessage" : "Error connecting to 192.168.1.51:27025 :: caused by :: Connection refused",
			"syncingTo" : "",
			"syncSourceHost" : "",
			"syncSourceId" : -1,
			"infoMessage" : "",
			"configVersion" : -1
		}
	],
	"ok" : 1,
	"operationTime" : Timestamp(1718444734, 1),
	"$gleStats" : {
		"lastOpTime" : Timestamp(0, 0),
		"electionId" : ObjectId("7fffffff0000000000000003")
	},
	"lastCommittedOpTime" : Timestamp(1718444703, 1),
	"$configServerState" : {
		"opTime" : {
			"ts" : Timestamp(1718444739, 1),
			"t" : NumberLong(1)
		}
	},
	"$clusterTime" : {
		"clusterTime" : Timestamp(1718444739, 1),
		"signature" : {
			"hash" : BinData(0,"AAAAAAAAAAAAAAAAAAAAAAAAAAA="),
			"keyId" : NumberLong(0)
		}
	}
}

现在变成了,一个主库和一个仲裁节点。
且原来的主库:27025无法连接。所以,可以看到确实已经完成了,自动故障切换。

3.新增数据并重启宕机的节点

shard1:PRIMARY> db.test1.insert({"id":1,"name":"薛双奇"})
WriteResult({ "nInserted" : 1 })
shard1:PRIMARY> db.test1.insert({"id":2,"name":"薛双奇2"})
WriteResult({ "nInserted" : 1 })
shard1:PRIMARY> db.test1.insert({"id":3,"name":"薛双奇3"})
WriteResult({ "nInserted" : 1 })
--新主节点插入的数据。
shard1:PRIMARY> db.test1.find()
{ "_id" : ObjectId("666d63abfc41b781c917bc01"), "id" : 1, "name" : "薛双奇" }
{ "_id" : ObjectId("666d63b2fc41b781c917bc02"), "id" : 2, "name" : "薛双奇2" }
{ "_id" : ObjectId("666d63b8fc41b781c917bc03"), "id" : 3, "name" : "薛双奇3" }
shard1:PRIMARY> 


--检查集群状态。
shard1:PRIMARY> rs.status()
{
	"set" : "shard1",
	"date" : ISODate("2024-06-15T09:51:51.449Z"),
	"myState" : 1,
	"term" : NumberLong(4),
	"syncingTo" : "",
	"syncSourceHost" : "",
	"syncSourceId" : -1,
	"heartbeatIntervalMillis" : NumberLong(2000),
	"optimes" : {
		"lastCommittedOpTime" : {
			"ts" : Timestamp(1718445106, 1),
			"t" : NumberLong(4)
		},
		"readConcernMajorityOpTime" : {
			"ts" : Timestamp(1718445106, 1),
			"t" : NumberLong(4)
		},
		"appliedOpTime" : {
			"ts" : Timestamp(1718445106, 1),
			"t" : NumberLong(4)
		},
		"durableOpTime" : {
			"ts" : Timestamp(1718445106, 1),
			"t" : NumberLong(4)
		}
	},
	"lastStableCheckpointTimestamp" : Timestamp(1718444703, 1),
	"members" : [
		{
			"_id" : 0,
			"name" : "192.168.1.51:27023",
			"health" : 1,
			"state" : 2,
			"stateStr" : "SECONDARY",
			"uptime" : 57,
			"optime" : {
				"ts" : Timestamp(1718445106, 1),
				"t" : NumberLong(4)
			},
			"optimeDurable" : {
				"ts" : Timestamp(1718445106, 1),
				"t" : NumberLong(4)
			},
			"optimeDate" : ISODate("2024-06-15T09:51:46Z"),
			"optimeDurableDate" : ISODate("2024-06-15T09:51:46Z"),
			"lastHeartbeat" : ISODate("2024-06-15T09:51:51.021Z"),
			"lastHeartbeatRecv" : ISODate("2024-06-15T09:51:51.157Z"),
			"pingMs" : NumberLong(0),
			"lastHeartbeatMessage" : "",
			"syncingTo" : "192.168.1.51:27025",
			"syncSourceHost" : "192.168.1.51:27025",
			"syncSourceId" : 2,
			"infoMessage" : "",
			"configVersion" : 7
		},
		{
			"_id" : 1,
			"name" : "192.168.1.51:27024",
			"health" : 1,
			"state" : 7,
			"stateStr" : "ARBITER",
			"uptime" : 57,
			"lastHeartbeat" : ISODate("2024-06-15T09:51:51.021Z"),
			"lastHeartbeatRecv" : ISODate("2024-06-15T09:51:50.625Z"),
			"pingMs" : NumberLong(0),
			"lastHeartbeatMessage" : "",
			"syncingTo" : "",
			"syncSourceHost" : "",
			"syncSourceId" : -1,
			"infoMessage" : "",
			"configVersion" : 7
		},
		{
			"_id" : 2,
			"name" : "192.168.1.51:27025",
			"health" : 1,
			"state" : 1,
			"stateStr" : "PRIMARY",
			"uptime" : 60,
			"optime" : {
				"ts" : Timestamp(1718445106, 1),
				"t" : NumberLong(4)
			},
			"optimeDate" : ISODate("2024-06-15T09:51:46Z"),
			"syncingTo" : "",
			"syncSourceHost" : "",
			"syncSourceId" : -1,
			"infoMessage" : "",
			"electionTime" : Timestamp(1718445064, 2),
			"electionDate" : ISODate("2024-06-15T09:51:04Z"),
			"configVersion" : 7,
			"self" : true,
			"lastHeartbeatMessage" : ""
		}
	],
	"ok" : 1,
	"operationTime" : Timestamp(1718445106, 1),
	"$gleStats" : {
		"lastOpTime" : Timestamp(0, 0),
		"electionId" : ObjectId("7fffffff0000000000000004")
	},
	"lastCommittedOpTime" : Timestamp(1718445106, 1),
	"$configServerState" : {
		"opTime" : {
			"ts" : Timestamp(1718445106, 1),
			"t" : NumberLong(1)
		}
	},
	"$clusterTime" : {
		"clusterTime" : Timestamp(1718445106, 1),
		"signature" : {
			"hash" : BinData(0,"AAAAAAAAAAAAAAAAAAAAAAAAAAA="),
			"keyId" : NumberLong(0)
		}
	}
}

---我们发现原来的27025又变回了主节点。
shard1:PRIMARY> use test; 
switched to db test
shard1:PRIMARY> show tables; 
test1
testindx
users
shard1:PRIMARY> db.test1.find()
{ "_id" : ObjectId("666d63b8fc41b781c917bc03"), "id" : 3, "name" : "薛双奇3" }
{ "_id" : ObjectId("666d63b2fc41b781c917bc02"), "id" : 2, "name" : "薛双奇2" }
{ "_id" : ObjectId("666d63abfc41b781c917bc01"), "id" : 1, "name" : "薛双奇" }
shard1:PRIMARY> 

4.总结

--27025 宕机后,中27023是主节点,我们在27023上插入了test1表。
--重启 27025 后,它不仅同步了丢失的部分数据。而且又自动切换为主节点了。
--这里的主要原因是,初始化集群时的优先级。

--我们回顾下初始化的章节里。27023优先级为1,所以自动变成了主。
--说明优先级越低,就会发生抢占情况,自动优先变长主节点。

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