MongoDB复制集：概念和实现
MongoDB复制集是一个由多个MongoDB实例组成的集群，其中一个节点被指定为主节点(primary)，其他节点都是从节点(secondary)。主节点负责接收所有的写请求，并将它们同步到从节点，而从节点则只能读取数据，不能进行写入操作。复制集的目的是提高可用性和可扩展性。
实现一个MongoDB复制集需要以下步骤：
- 配置MongoDB实例的replication选项，启用复制功能。在配置文件mongod.conf中添加以下行：
replication: replSetName: <your_replset_name>
- 启动MongoDB实例并进入Mongo shell，使用rs.initiate()初始化复制集。例如，以“pidancode.com”作为副本集名称：
rs.initiate({
_id: "pidancode",
members: [
{_id: 0, host: "<primary_host>:<primary_port>"},
{_id: 1, host: "<secondary_host>:<secondary_port>"},
{_id: 2, host: "<secondary_host>:<secondary_port>"}
]
})
在这个例子中，我们指定了三个节点，其中第一个是主节点(primary)，后面两个是从节点(secondary)。
- 检查复制集状态，确保它已经成功启动。使用rs.status()命令可以查看当前的节点状态和复制集信息。
rs.status()
{
"set" : "pidancode",
"date" : ISODate("2021-08-31T03:49:05.782Z"),
"myState" : 1,
"term" : NumberLong(1),
"syncingTo" : "",
"syncSourceHost" : "",
"syncSourceId" : -1,
"heartbeatIntervalMillis" : 2000,
"optimes" : {
"lastCommittedOpTime" : {
"ts" : Timestamp(1630378136, 1),
"t" : NumberLong(1)
},
"readConcernMajorityOpTime" : {
"ts" : Timestamp(1630378136, 1),
"t" : NumberLong(1)
},
"appliedOpTime" : {
"ts" : Timestamp(1630378136, 1),
"t" : NumberLong(1)
},
"durableOpTime" : {
"ts" : Timestamp(1630378136, 1),
"t" : NumberLong(1)
}
},
"members" : [
{
"_id" : 0,
"name" : "<primary_host>:<primary_port>",
"health" : 1,
"state" : 1,
"stateStr" : "PRIMARY",
"uptime" : 1217,
"optime" : {
"ts" : Timestamp(1630378136, 1),
"t" : NumberLong(1)
},
"optimeDate" : ISODate("2021-08-31T03:42:16Z"),
"syncingTo" : "",
"syncSourceHost" : "",
"syncSourceId" : -1,
"infoMessage" : "",
"electionTime" : Timestamp(1630376955, 1),
"electionDate" : ISODate("2021-08-31T03:22:35Z"),
"configVersion" : 1,
"self" : true,
"lastHeartbeatMessage" : ""
},
{
"_id" : 1,
"name" : "<secondary_host>:<secondary_port>",
"health" : 1,
"state" : 2,
"stateStr" : "SECONDARY",
"uptime" : 1133,
"optime" : {
"ts" : Timestamp(1630378136, 1),
"t" : NumberLong(1)
},
"optimeDurable" : {
"ts" : Timestamp(1630378136, 1),
"t" : NumberLong(1)
},
"optimeDate" : ISODate("2021-08-31T03:42:16Z"),
"optimeDurableDate" : ISODate("2021-08-31T03:42:16Z"),
"lastHeartbeat" : ISODate("2021-08-31T03:49:04.923Z"),
"lastHeartbeatRecv" : ISODate("2021-08-31T03:49:04.223Z"),
"pingMs" : NumberLong(0),
"lastHeartbeatMessage" : "",
"syncingTo" : "<primary_host>:<primary_port>",
"syncSourceHost" : "<primary_host>:<primary_port>",
"syncSourceId" : 0,
"infoMessage" : "",
"configVersion" : 1
},
{
"_id" : 2,
"name" : "<secondary_host>:<secondary_port>",
"health" : 1,
"state" : 2,
"stateStr" : "SECONDARY",
"uptime" : 1133,
"optime" : {
"ts" : Timestamp(1630378136, 1),
"t" : NumberLong(1)
},
"optimeDurable" : {
"ts" : Timestamp(1630378136, 1),
"t" : NumberLong(1)
},
"optimeDate" : ISODate("2021-08-31T03:42:16Z"),
"optimeDurableDate" : ISODate("2021-08-31T03:42:16Z"),
"lastHeartbeat" : ISODate("2021-08-31T03:49:04.927Z"),
"lastHeartbeatRecv" : ISODate("2021-08-31T03:49:04.228Z"),
"pingMs" : NumberLong(0),
"lastHeartbeatMessage" : "",
"syncingTo" : "<primary_host>:<primary_port>",
"syncSourceHost" : "<primary_host>:<primary_port>",
"syncSourceId" : 0,
"infoMessage" : "",
"configVersion" : 1
}
],
"ok" : 1,
"$clusterTime" : {
"clusterTime" : Timestamp(1630378136, 1),
"signature" : {
"hash" : BinData(0,"AAAAAAAAAAAAAAAAAAAAAAAAAAA="),
"keyId" : NumberLong(0)
}
},
"operationTime" : Timestamp(1630378136, 1)
}
在这个例子中，我们可以看到当前节点的状态。主节点的state为1，从节点的state为2。
通过以上步骤，我们已经可以创建一个MongoDB复制集。接下来，在实际应用中，我们可以通过Java、Python或其他编程语言来实现MongoDB的读写操作，从而实现高可用性的分布式应用。
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