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How To Setup MongoDB 4.0 Replica Set

时间：2018-08-23 17:02:29      阅读：186      评论：0      收藏：0      [点我收藏+]

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本文介绍如何配置MongoDB的Replica Set服务，并介绍了如何做主从切换以及添加新节点。此环境都在一台服务器上完成。

1、配置MongoDB Replica Set

1.1 创建配置文件

[root@hdp05 ~]# mkdir -p /data/rep{1,2}
[root@hdp05 ~]# chown mongod:mongod /data/rep*
[root@hdp05 ~]# vi /data/rep1/mongod.rep1
net:
  bindIp: 0.0.0.0
  port: 27019
processManagement:
  fork: "true"
replication:
  replSetName: TestRepSet
storage:
  dbPath: /data/rep1
systemLog:
  destination: file
  path: /data/rep1/mongod.log
[root@hdp05 ~]# vi /data/rep2/mongod.rep2
net:
  bindIp: 0.0.0.0
  port: 27020
processManagement:
  fork: "true"
replication:
  replSetName: TestRepSet
storage:
  dbPath: /data/rep2
systemLog:
  destination: file
  path: /data/rep2/mongod.log

1.2 启动MongoDB服务

[root@hdp05 ~]# mongod -f /data/rep1/mongod.rep1
[root@hdp05 ~]# mongod -f /data/rep2/mongod.rep2

1.3 初始化Replica Set

[root@hdp05 ~]# mongo --port 27019
> rs.initiate( {_id : "TestRepSet",members: [{ _id: 0, host: "hdp05.thinkjoy.tt:27019" },{ _id: 1, host: "hdp05.thinkjoy.tt:27020" }]})
{
        "ok" : 1,
        "operationTime" : Timestamp(1534909723, 1),
        "$clusterTime" : {
                "clusterTime" : Timestamp(1534909723, 1),
                "signature" : {
                        "hash" : BinData(0,"AAAAAAAAAAAAAAAAAAAAAAAAAAA="),
                        "keyId" : NumberLong(0)
                }
        }
}
--检查配置信息
TestRepSet:SECONDARY> rs.conf()
{
        "_id" : "TestRepSet",
        "version" : 1,
        "protocolVersion" : NumberLong(1),
        "writeConcernMajorityJournalDefault" : true,
        "members" : [
                {
                        "_id" : 0,
                        "host" : "hdp05.thinkjoy.tt:27019",
                        "arbiterOnly" : false,
                        "buildIndexes" : true,
                        "hidden" : false,
                        "priority" : 1,
                        "tags" : {

                        },
                        "slaveDelay" : NumberLong(0),
                        "votes" : 1
                },
                {
                        "_id" : 1,
                        "host" : "hdp05.thinkjoy.tt:27020",
                        "arbiterOnly" : false,
                        "buildIndexes" : true,
                        "hidden" : false,
                        "priority" : 1,
                        "tags" : {

                        },
                        "slaveDelay" : NumberLong(0),
                        "votes" : 1
                }
        ],
        "settings" : {
                "chainingAllowed" : true,
                "heartbeatIntervalMillis" : 2000,
                "heartbeatTimeoutSecs" : 10,
                "electionTimeoutMillis" : 10000,
                "catchUpTimeoutMillis" : -1,
                "catchUpTakeoverDelayMillis" : 30000,
                "getLastErrorModes" : {

                },
                "getLastErrorDefaults" : {
                        "w" : 1,
                        "wtimeout" : 0
                },
                "replicaSetId" : ObjectId("5b7cdd1ba00297bd3f560eda")
        }
}
--确认primary节点
TestRepSet:PRIMARY>  db.isMaster()
{
        "hosts" : [
                "hdp05.thinkjoy.tt:27019",
                "hdp05.thinkjoy.tt:27020"
        ],
        "setName" : "TestRepSet",
        "setVersion" : 1,
        "ismaster" : true,
        "secondary" : false,
        "primary" : "hdp05.thinkjoy.tt:27019",
        "me" : "hdp05.thinkjoy.tt:27019",
        "electionId" : ObjectId("7fffffff0000000000000001"),
        "lastWrite" : {
                "opTime" : {
                        "ts" : Timestamp(1534988860, 1),
                        "t" : NumberLong(1)
                },
                "lastWriteDate" : ISODate("2018-08-23T01:47:40Z"),
                "majorityOpTime" : {
                        "ts" : Timestamp(1534988860, 1),
                        "t" : NumberLong(1)
                },
                "majorityWriteDate" : ISODate("2018-08-23T01:47:40Z")
        },
        "maxBsonObjectSize" : 16777216,
        "maxMessageSizeBytes" : 48000000,
        "maxWriteBatchSize" : 100000,
        "localTime" : ISODate("2018-08-23T01:47:49.713Z"),
        "logicalSessionTimeoutMinutes" : 30,
        "minWireVersion" : 0,
        "maxWireVersion" : 7,
        "readOnly" : false,
        "ok" : 1,
        "operationTime" : Timestamp(1534988860, 1),
        "$clusterTime" : {
                "clusterTime" : Timestamp(1534988860, 1),
                "signature" : {
                        "hash" : BinData(0,"AAAAAAAAAAAAAAAAAAAAAAAAAAA="),
                        "keyId" : NumberLong(0)
                }
        }
}

到此，整个Replica Set配置完成。

2、添加新的secondary节点

2.1 创建配置文件以及数据目录

[root@hdp05 ~]# mkdir /data/rep3;chown mongod:mongod /data/rep3
[root@hdp05 ~]# vi /data/rep3/mongod.rep3 
net:
  bindIp: 0.0.0.0
  port: 27021
processManagement:
  fork: "true"
replication:
  replSetName: TestRepSet
storage:
  dbPath: /data/rep3
systemLog:
  destination: file
  path: /data/rep3/mongod.log

2.2 启动MongoDB服务

[root@hdp05 ~]# mongod -f /data/rep3/mongod.rep3

2.3 向Replica Set添加节点

使用mongo连接到主节点，如果不知道主节点是哪个，则连接到任意一个几点，使用db.isMaster()或者rs.status()确认那个是主节点。

[root@hdp05 ~]# mongo --port 27019
TestRepSet:PRIMARY>  db.isMaster()
--添加节点
TestRepSet:PRIMARY> rs.add( { host: "hdp05.thinkjoy.tt:27021", priority: 0, votes: 0 } )
{
        "ok" : 1,
        "operationTime" : Timestamp(1534989374, 1),
        "$clusterTime" : {
                "clusterTime" : Timestamp(1534989374, 1),
                "signature" : {
                        "hash" : BinData(0,"AAAAAAAAAAAAAAAAAAAAAAAAAAA="),
                        "keyId" : NumberLong(0)
                }
        }
}
TestRepSet:PRIMARY> rs.status()
{
        "set" : "TestRepSet",
        "date" : ISODate("2018-08-23T01:56:47.591Z"),
        "myState" : 1,
        "term" : NumberLong(1),
        "syncingTo" : "",
        "syncSourceHost" : "",
        "syncSourceId" : -1,
        "heartbeatIntervalMillis" : NumberLong(2000),
        "optimes" : {
                "lastCommittedOpTime" : {
                        "ts" : Timestamp(1534989400, 1),
                        "t" : NumberLong(1)
                },
                "readConcernMajorityOpTime" : {
                        "ts" : Timestamp(1534989400, 1),
                        "t" : NumberLong(1)
                },
                "appliedOpTime" : {
                        "ts" : Timestamp(1534989400, 1),
                        "t" : NumberLong(1)
                },
                "durableOpTime" : {
                        "ts" : Timestamp(1534989400, 1),
                        "t" : NumberLong(1)
                }
        },
        "lastStableCheckpointTimestamp" : Timestamp(1534989390, 1),
        "members" : [
                {
                        "_id" : 0,
                        "name" : "hdp05.thinkjoy.tt:27019",
                        "health" : 1,
                        "state" : 1,
                        "stateStr" : "PRIMARY",
                        "uptime" : 79787,
                        "optime" : {
                                "ts" : Timestamp(1534989400, 1),
                                "t" : NumberLong(1)
                        },
                        "optimeDate" : ISODate("2018-08-23T01:56:40Z"),
                        "syncingTo" : "",
                        "syncSourceHost" : "",
                        "syncSourceId" : -1,
                        "infoMessage" : "",
                        "electionTime" : Timestamp(1534909735, 1),
                        "electionDate" : ISODate("2018-08-22T03:48:55Z"),
                        "configVersion" : 2,
                        "self" : true,
                        "lastHeartbeatMessage" : ""
                },
                {
                        "_id" : 1,
                        "name" : "hdp05.thinkjoy.tt:27020",
                        "health" : 1,
                        "state" : 2,
                        "stateStr" : "SECONDARY",
                        "uptime" : 79683,
                        "optime" : {
                                "ts" : Timestamp(1534989400, 1),
                                "t" : NumberLong(1)
                        },
                        "optimeDurable" : {
                                "ts" : Timestamp(1534989400, 1),
                                "t" : NumberLong(1)
                        },
                        "optimeDate" : ISODate("2018-08-23T01:56:40Z"),
                        "optimeDurableDate" : ISODate("2018-08-23T01:56:40Z"),
                        "lastHeartbeat" : ISODate("2018-08-23T01:56:46.530Z"),
                        "lastHeartbeatRecv" : ISODate("2018-08-23T01:56:47.554Z"),
                        "pingMs" : NumberLong(0),
                        "lastHeartbeatMessage" : "",
                        "syncingTo" : "hdp05.thinkjoy.tt:27019",
                        "syncSourceHost" : "hdp05.thinkjoy.tt:27019",
                        "syncSourceId" : 0,
                        "infoMessage" : "",
                        "configVersion" : 2
                },
                {
                        "_id" : 2,
                        "name" : "hdp05.thinkjoy.tt:27021",
                        "health" : 1,
                        "state" : 2,
                        "stateStr" : "SECONDARY",
                        "uptime" : 33,
                        "optime" : {
                                "ts" : Timestamp(1534989400, 1),
                                "t" : NumberLong(1)
                        },
                        "optimeDurable" : {
                                "ts" : Timestamp(1534989400, 1),
                                "t" : NumberLong(1)
                        },
                        "optimeDate" : ISODate("2018-08-23T01:56:40Z"),
                        "optimeDurableDate" : ISODate("2018-08-23T01:56:40Z"),
                        "lastHeartbeat" : ISODate("2018-08-23T01:56:46.530Z"),
                        "lastHeartbeatRecv" : ISODate("2018-08-23T01:56:45.716Z"),
                        "pingMs" : NumberLong(0),
                        "lastHeartbeatMessage" : "",
                        "syncingTo" : "hdp05.thinkjoy.tt:27019",
                        "syncSourceHost" : "hdp05.thinkjoy.tt:27019",
                        "syncSourceId" : 0,
                        "infoMessage" : "",
                        "configVersion" : 2
                }
        ],
        "ok" : 1,
        "operationTime" : Timestamp(1534989400, 1),
        "$clusterTime" : {
                "clusterTime" : Timestamp(1534989400, 1),
                "signature" : {
                        "hash" : BinData(0,"AAAAAAAAAAAAAAAAAAAAAAAAAAA="),
                        "keyId" : NumberLong(0)
                }
        }
}
--设置每个节点的优先级
TestRepSet:PRIMARY> var cfg = rs.conf();
TestRepSet:PRIMARY> cfg.members[2].priority = 1
TestRepSet:PRIMARY> cfg.members[2].votes = 1
TestRepSet:PRIMARY> rs.reconfig(cfg)
{
        "ok" : 1,
        "operationTime" : Timestamp(1534989596, 1),
        "$clusterTime" : {
                "clusterTime" : Timestamp(1534989596, 1),
                "signature" : {
                        "hash" : BinData(0,"AAAAAAAAAAAAAAAAAAAAAAAAAAA="),
                        "keyId" : NumberLong(0)
                }
        }
}

3、Replica Set主从切换

官方提供的切换方式有两种：一种是通过设置优先级进行切换，另外一种是通过MongoDB的命令进行切换。

3.1 设置优先级切换

当前三个节点的优先级都是1，而27019是primary节点，通过降低27019和27020端口对应节点的优先级，使27021对应的节点成为primary节点。

[root@hdp05 ~]# mongo --port 27019
--切换前的主从信息
TestRepSet:PRIMARY> db.isMaster()
{
        "hosts" : [
                "hdp05.thinkjoy.tt:27019",
                "hdp05.thinkjoy.tt:27020",
                "hdp05.thinkjoy.tt:27021"
        ],
        "setName" : "TestRepSet",
        "setVersion" : 6,
        "ismaster" : true,
        "secondary" : false,
        "primary" : "hdp05.thinkjoy.tt:27019",
        "me" : "hdp05.thinkjoy.tt:27019",
        "electionId" : ObjectId("7fffffff0000000000000009"),
        "lastWrite" : {
                "opTime" : {
                        "ts" : Timestamp(1535009522, 1),
                        "t" : NumberLong(9)
                },
                "lastWriteDate" : ISODate("2018-08-23T07:32:02Z"),
                "majorityOpTime" : {
                        "ts" : Timestamp(1535009522, 1),
                        "t" : NumberLong(9)
                },
                "majorityWriteDate" : ISODate("2018-08-23T07:32:02Z")
        },
        "maxBsonObjectSize" : 16777216,
        "maxMessageSizeBytes" : 48000000,
        "maxWriteBatchSize" : 100000,
        "localTime" : ISODate("2018-08-23T07:32:06.129Z"),
        "logicalSessionTimeoutMinutes" : 30,
        "minWireVersion" : 0,
        "maxWireVersion" : 7,
        "readOnly" : false,
        "ok" : 1,
        "operationTime" : Timestamp(1535009522, 1),
        "$clusterTime" : {
                "clusterTime" : Timestamp(1535009522, 1),
                "signature" : {
                        "hash" : BinData(0,"AAAAAAAAAAAAAAAAAAAAAAAAAAA="),
                        "keyId" : NumberLong(0)
                }
        }
}
--执行切换
TestRepSet:PRIMARY> cfg = rs.conf()
TestRepSet:PRIMARY> cfg.members[0].priority = 0.5
TestRepSet:PRIMARY> cfg.members[1].priority = 0.5
TestRepSet:PRIMARY> cfg.members[2].priority = 1
TestRepSet:PRIMARY> rs.reconfig(cfg)
--切换后的主从信息
[root@hdp05 ~]# mongo --port 27021
TestRepSet:PRIMARY> rs.status()
{
        "set" : "TestRepSet",
        "date" : ISODate("2018-08-23T03:30:47.189Z"),
        "myState" : 1,
        "term" : NumberLong(2),
        "syncingTo" : "",
        "syncSourceHost" : "",
        "syncSourceId" : -1,
        "heartbeatIntervalMillis" : NumberLong(2000),
        "optimes" : {
                "lastCommittedOpTime" : {
                        "ts" : Timestamp(1534995039, 1),
                        "t" : NumberLong(2)
                },
                "readConcernMajorityOpTime" : {
                        "ts" : Timestamp(1534995039, 1),
                        "t" : NumberLong(2)
                },
                "appliedOpTime" : {
                        "ts" : Timestamp(1534995039, 1),
                        "t" : NumberLong(2)
                },
                "durableOpTime" : {
                        "ts" : Timestamp(1534995039, 1),
                        "t" : NumberLong(2)
                }
        },
        "lastStableCheckpointTimestamp" : Timestamp(1534995029, 1),
        "members" : [
                {
                        "_id" : 0,
                        "name" : "hdp05.thinkjoy.tt:27019",
                        "health" : 1,
                        "state" : 2,
                        "stateStr" : "SECONDARY",
                        "uptime" : 5672,
                        "optime" : {
                                "ts" : Timestamp(1534995039, 1),
                                "t" : NumberLong(2)
                        },
                        "optimeDurable" : {
                                "ts" : Timestamp(1534995039, 1),
                                "t" : NumberLong(2)
                        },
                        "optimeDate" : ISODate("2018-08-23T03:30:39Z"),
                        "optimeDurableDate" : ISODate("2018-08-23T03:30:39Z"),
                        "lastHeartbeat" : ISODate("2018-08-23T03:30:47.048Z"),
                        "lastHeartbeatRecv" : ISODate("2018-08-23T03:30:46.990Z"),
                        "pingMs" : NumberLong(0),
                        "lastHeartbeatMessage" : "",
                        "syncingTo" : "hdp05.thinkjoy.tt:27021",
                        "syncSourceHost" : "hdp05.thinkjoy.tt:27021",
                        "syncSourceId" : 2,
                        "infoMessage" : "",
                        "configVersion" : 5
                },
                {
                        "_id" : 1,
                        "name" : "hdp05.thinkjoy.tt:27020",
                        "health" : 1,
                        "state" : 2,
                        "stateStr" : "SECONDARY",
                        "uptime" : 5672,
                        "optime" : {
                                "ts" : Timestamp(1534995039, 1),
                                "t" : NumberLong(2)
                        },
                        "optimeDurable" : {
                                "ts" : Timestamp(1534995039, 1),
                                "t" : NumberLong(2)
                        },
                        "optimeDate" : ISODate("2018-08-23T03:30:39Z"),
                        "optimeDurableDate" : ISODate("2018-08-23T03:30:39Z"),
                        "lastHeartbeat" : ISODate("2018-08-23T03:30:46.991Z"),
                        "lastHeartbeatRecv" : ISODate("2018-08-23T03:30:46.991Z"),
                        "pingMs" : NumberLong(0),
                        "lastHeartbeatMessage" : "",
                        "syncingTo" : "hdp05.thinkjoy.tt:27021",
                        "syncSourceHost" : "hdp05.thinkjoy.tt:27021",
                        "syncSourceId" : 2,
                        "infoMessage" : "",
                        "configVersion" : 5
                },
                {
                        "_id" : 2,
                        "name" : "hdp05.thinkjoy.tt:27021",
                        "health" : 1,
                        "state" : 1,
                        "stateStr" : "PRIMARY",
                        "uptime" : 5957,
                        "optime" : {
                                "ts" : Timestamp(1534995039, 1),
                                "t" : NumberLong(2)
                        },
                        "optimeDate" : ISODate("2018-08-23T03:30:39Z"),
                        "syncingTo" : "",
                        "syncSourceHost" : "",
                        "syncSourceId" : -1,
                        "infoMessage" : "",
                        "electionTime" : Timestamp(1534994548, 1),
                        "electionDate" : ISODate("2018-08-23T03:22:28Z"),
                        "configVersion" : 5,
                        "self" : true,
                        "lastHeartbeatMessage" : ""
                }
        ],
        "ok" : 1,
        "operationTime" : Timestamp(1534995039, 1),
        "$clusterTime" : {
                "clusterTime" : Timestamp(1534995039, 1),
                "signature" : {
                        "hash" : BinData(0,"AAAAAAAAAAAAAAAAAAAAAAAAAAA="),
                        "keyId" : NumberLong(0)
                }
        }
}

3.2 使用MongoDB命令切换

--通过数据库命令切换
验证主从信息：
[root@hdp05 ~]# mongo --port 27021
TestRepSet:PRIMARY> rs.status()
--冻结即将成为主节点的从节点
[root@hdp05 ~]# mongo --port 27021
TestRepSet:PRIMARY> rs.freeze(120)
{
        "ok" : 1,
        "operationTime" : Timestamp(1534995549, 1),
        "$clusterTime" : {
                "clusterTime" : Timestamp(1534995549, 1),
                "signature" : {
                        "hash" : BinData(0,"AAAAAAAAAAAAAAAAAAAAAAAAAAA="),
                        "keyId" : NumberLong(0)
                }
        }
}
TestRepSet:PRIMARY> rs.stepDown(120)
2018-08-23T14:24:50.897+0800 E QUERY    [js] Error: error doing query: failed: network error while attempting to run command ‘replSetStepDown‘ on host ‘127.0.0.1:27021‘  :
DB.prototype.runCommand@src/mongo/shell/db.js:168:1
DB.prototype.adminCommand@src/mongo/shell/db.js:186:16
rs.stepDown@src/mongo/shell/utils.js:1433:12
@(shell):1:1
2018-08-23T14:24:50.899+0800 I NETWORK  [js] trying reconnect to 127.0.0.1:27021 failed
2018-08-23T14:24:50.900+0800 I NETWORK  [js] reconnect 127.0.0.1:27021 ok
TestRepSet:SECONDARY> 
TestRepSet:SECONDARY> rs.status()
{
        "set" : "TestRepSet",
        "date" : ISODate("2018-08-23T06:25:03.529Z"),
        "myState" : 2,
        "term" : NumberLong(6),
        "syncingTo" : "hdp05.thinkjoy.tt:27019",
        "syncSourceHost" : "hdp05.thinkjoy.tt:27019",
        "syncSourceId" : 0,
        "heartbeatIntervalMillis" : NumberLong(2000),
        "optimes" : {
                "lastCommittedOpTime" : {
                        "ts" : Timestamp(1535005502, 1),
                        "t" : NumberLong(6)
                },
                "readConcernMajorityOpTime" : {
                        "ts" : Timestamp(1535005502, 1),
                        "t" : NumberLong(6)
                },
                "appliedOpTime" : {
                        "ts" : Timestamp(1535005502, 1),
                        "t" : NumberLong(6)
                },
                "durableOpTime" : {
                        "ts" : Timestamp(1535005502, 1),
                        "t" : NumberLong(6)
                }
        },
        "lastStableCheckpointTimestamp" : Timestamp(1535005472, 1),
        "members" : [
                {
                        "_id" : 0,
                        "name" : "hdp05.thinkjoy.tt:27019",
                        "health" : 1,
                        "state" : 1,
                        "stateStr" : "PRIMARY",
                        "uptime" : 16128,
                        "optime" : {
                                "ts" : Timestamp(1535005502, 1),
                                "t" : NumberLong(6)
                        },
                        "optimeDurable" : {
                                "ts" : Timestamp(1535005502, 1),
                                "t" : NumberLong(6)
                        },
                        "optimeDate" : ISODate("2018-08-23T06:25:02Z"),
                        "optimeDurableDate" : ISODate("2018-08-23T06:25:02Z"),
                        "lastHeartbeat" : ISODate("2018-08-23T06:25:03.297Z"),
                        "lastHeartbeatRecv" : ISODate("2018-08-23T06:25:02.640Z"),
                        "pingMs" : NumberLong(0),
                        "lastHeartbeatMessage" : "",
                        "syncingTo" : "",
                        "syncSourceHost" : "",
                        "syncSourceId" : -1,
                        "infoMessage" : "",
                        "electionTime" : Timestamp(1535005500, 1),
                        "electionDate" : ISODate("2018-08-23T06:25:00Z"),
                        "configVersion" : 5
                },
                {
                        "_id" : 1,
                        "name" : "hdp05.thinkjoy.tt:27020",
                        "health" : 1,
                        "state" : 2,
                        "stateStr" : "SECONDARY",
                        "uptime" : 16128,
                        "optime" : {
                                "ts" : Timestamp(1535005482, 1),
                                "t" : NumberLong(5)
                        },
                        "optimeDurable" : {
                                "ts" : Timestamp(1535005482, 1),
                                "t" : NumberLong(5)
                        },
                        "optimeDate" : ISODate("2018-08-23T06:24:42Z"),
                        "optimeDurableDate" : ISODate("2018-08-23T06:24:42Z"),
                        "lastHeartbeat" : ISODate("2018-08-23T06:25:03.297Z"),
                        "lastHeartbeatRecv" : ISODate("2018-08-23T06:25:03.479Z"),
                        "pingMs" : NumberLong(0),
                        "lastHeartbeatMessage" : "",
                        "syncingTo" : "",
                        "syncSourceHost" : "",
                        "syncSourceId" : -1,
                        "infoMessage" : "",
                        "configVersion" : 5
                },
                {
                        "_id" : 2,
                        "name" : "hdp05.thinkjoy.tt:27021",
                        "health" : 1,
                        "state" : 2,
                        "stateStr" : "SECONDARY",
                        "uptime" : 16413,
                        "optime" : {
                                "ts" : Timestamp(1535005502, 1),
                                "t" : NumberLong(6)
                        },
                        "optimeDate" : ISODate("2018-08-23T06:25:02Z"),
                        "syncingTo" : "hdp05.thinkjoy.tt:27019",
                        "syncSourceHost" : "hdp05.thinkjoy.tt:27019",
                        "syncSourceId" : 0,
                        "infoMessage" : "syncing from: hdp05.thinkjoy.tt:27019",
                        "configVersion" : 5,
                        "self" : true,
                        "lastHeartbeatMessage" : ""
                }
        ],
        "ok" : 1,
        "operationTime" : Timestamp(1535005502, 1),
        "$clusterTime" : {
                "clusterTime" : Timestamp(1535005502, 1),
                "signature" : {
                        "hash" : BinData(0,"AAAAAAAAAAAAAAAAAAAAAAAAAAA="),
                        "keyId" : NumberLong(0)
                }
        }
}

4、从节点读取数据

默认情况下，secondary节点时不允许读操作的，否则会遇到下面的报错：

TestRepSet:SECONDARY> show dbs
2018-08-23T15:41:31.667+0800 E QUERY    [js] Error: listDatabases failed:{
        "operationTime" : Timestamp(1535010084, 1),
        "ok" : 0,
        "errmsg" : "not master and slaveOk=false",
        "code" : 13435,
        "codeName" : "NotMasterNoSlaveOk",
        "$clusterTime" : {
                "clusterTime" : Timestamp(1535010084, 1),
                "signature" : {
                        "hash" : BinData(0,"AAAAAAAAAAAAAAAAAAAAAAAAAAA="),
                        "keyId" : NumberLong(0)
                }
        }
} :
_getErrorWithCode@src/mongo/shell/utils.js:25:13
Mongo.prototype.getDBs@src/mongo/shell/mongo.js:67:1
shellHelper.show@src/mongo/shell/utils.js:876:19
shellHelper@src/mongo/shell/utils.js:766:15
@(shellhelp2):1:1

有时候为了降低primary节点的压力，需要使用secondary读写数据，这就需要用到MongoDB的slaveOkay参数，打开此参数后，就可以从secondary节点读写数据，如下：

TestRepSet:SECONDARY> rs.slaveOk();
TestRepSet:SECONDARY> show dbs
MyDB    1.672GB
admin   0.000GB
config  0.000GB
local   1.200GB
TestRepSet:SECONDARY>

5、更改oplog大小

主节点的操作记录成为oplog。它存储在一个特殊的数据库中，叫做local。oplog中的每个文档都代表主节点上执行的一个操作。oplog只记录改变数据库状态的操作，因为oplog只是作为主从节点保持数据同步的机制。
oplog的大小默认是剩余磁盘空间的5%。也可以在启动MongoDB时加上oplogSize参数指定大小。如果发现oplog大小满足不了时，可以使用下面的命令进行在线更改：

[root@hdp05 ~]# mongo --port 27019
TestRepSet:PRIMARY> use local
TestRepSet:PRIMARY> db.oplog.rs.stats().maxSize
NumberLong(1429872640)--显示出来的大小单位为字节
--设置oplog的大小为2048M
TestRepSet:PRIMARY> db.adminCommand({replSetResizeOplog: 1, size: 2048}) 

{
        "ok" : 1,
        "operationTime" : Timestamp(1534927347, 1),
        "$clusterTime" : {
                "clusterTime" : Timestamp(1534927347, 1),
                "signature" : {
                        "hash" : BinData(0,"AAAAAAAAAAAAAAAAAAAAAAAAAAA="),
                        "keyId" : NumberLong(0)
                }
        }
}
TestRepSet:PRIMARY> db.oplog.rs.stats().maxSize
NumberLong("2147483648")

How To Setup MongoDB 4.0 Replica Set

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原文地址：http://blog.51cto.com/candon123/2163439
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