mongo学习- 副本集 大多数原则

副本集中有一个重要的概念“大多数”，意思是说，选择主节点需要大多数决定（本人亲自做了实验）

步骤：

 1.开启副本集（如果没有配置好 副本集的 亲参考我的上篇文章  https://www.cnblogs.com/anxbb/p/9482304.html）

 2.运行 rs.status(),查看状态

{
    "set" : "haibin",
    "date" : ISODate("2018-08-16T03:18:05.461Z"),
    "myState" : 1,
    "term" : NumberLong(9),
    "heartbeatIntervalMillis" : NumberLong(2000),
    "optimes" : {
        "lastCommittedOpTime" : {
            "ts" : Timestamp(1534389483, 1),
            "t" : NumberLong(9)
        },
        "appliedOpTime" : {
            "ts" : Timestamp(1534389483, 1),
            "t" : NumberLong(9)
        },
        "durableOpTime" : {
            "ts" : Timestamp(1534389483, 1),
            "t" : NumberLong(9)
        }
    },
    "members" : [ 
        {
            "_id" : 0,
            "name" : "127.0.0.1:27017",
            "health" : 1.0,
            "state" : 1,
            "stateStr" : "PRIMARY",
            "uptime" : 788,
            "optime" : {
                "ts" : Timestamp(1534389483, 1),
                "t" : NumberLong(9)
            },
            "optimeDate" : ISODate("2018-08-16T03:18:03.000Z"),
            "electionTime" : Timestamp(1534389270, 1),
            "electionDate" : ISODate("2018-08-16T03:14:30.000Z"),
            "configVersion" : 2,
            "self" : true
        }, 
        {
            "_id" : 1,
            "name" : "127.0.0.1:27018",
            "health" : 1.0,
            "state" : 2,
            "stateStr" : "SECONDARY",
            "uptime" : 6,
            "optime" : {
                "ts" : Timestamp(1534389483, 1),
                "t" : NumberLong(9)
            },
            "optimeDurable" : {
                "ts" : Timestamp(1534389483, 1),
                "t" : NumberLong(9)
            },
            "optimeDate" : ISODate("2018-08-16T03:18:03.000Z"),
            "optimeDurableDate" : ISODate("2018-08-16T03:18:03.000Z"),
            "lastHeartbeat" : ISODate("2018-08-16T03:18:04.903Z"),
            "lastHeartbeatRecv" : ISODate("2018-08-16T03:18:03.874Z"),
            "pingMs" : NumberLong(0),
            "syncingTo" : "127.0.0.1:27017",
            "configVersion" : 2
        }, 
        {
            "_id" : 2,
            "name" : "127.0.0.1:27019",
            "health" : 1.0,
            "state" : 7,
            "stateStr" : "ARBITER",
            "uptime" : 221,
            "lastHeartbeat" : ISODate("2018-08-16T03:18:04.603Z"),
            "lastHeartbeatRecv" : ISODate("2018-08-16T03:18:04.103Z"),
            "pingMs" : NumberLong(0),
            "configVersion" : 2
        }
    ],
    "ok" : 1.0
}

　　3.试着关闭 27017这个端口 然后在运行 rs.status()，结果如下

{
    "set" : "haibin",
    "date" : ISODate("2018-08-16T03:20:21.708Z"),
    "myState" : 1,
    "term" : NumberLong(10),
    "heartbeatIntervalMillis" : NumberLong(2000),
    "optimes" : {
        "lastCommittedOpTime" : {
            "ts" : Timestamp(1534389603, 1),
            "t" : NumberLong(9)
        },
        "appliedOpTime" : {
            "ts" : Timestamp(1534389616, 1),
            "t" : NumberLong(10)
        },
        "durableOpTime" : {
            "ts" : Timestamp(1534389616, 1),
            "t" : NumberLong(10)
        }
    },
    "members" : [ 
        {
            "_id" : 0,
            "name" : "127.0.0.1:27017",
            "health" : 0.0,
            "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("1970-01-01T00:00:00.000Z"),
            "optimeDurableDate" : ISODate("1970-01-01T00:00:00.000Z"),
            "lastHeartbeat" : ISODate("2018-08-16T03:20:21.009Z"),
            "lastHeartbeatRecv" : ISODate("2018-08-16T03:20:02.982Z"),
            "pingMs" : NumberLong(0),
            "lastHeartbeatMessage" : "����Ŀ�������������ܾ����޷����ӡ�",
            "configVersion" : -1
        }, 
        {
            "_id" : 1,
            "name" : "127.0.0.1:27018",
            "health" : 1.0,
            "state" : 1,
            "stateStr" : "PRIMARY",
            "uptime" : 144,
            "optime" : {
                "ts" : Timestamp(1534389616, 1),
                "t" : NumberLong(10)
            },
            "optimeDate" : ISODate("2018-08-16T03:20:16.000Z"),
            "infoMessage" : "could not find member to sync from",
            "electionTime" : Timestamp(1534389614, 1),
            "electionDate" : ISODate("2018-08-16T03:20:14.000Z"),
            "configVersion" : 2,
            "self" : true
        }, 
        {
            "_id" : 2,
            "name" : "127.0.0.1:27019",
            "health" : 1.0,
            "state" : 7,
            "stateStr" : "ARBITER",
            "uptime" : 142,
            "lastHeartbeat" : ISODate("2018-08-16T03:20:20.912Z"),
            "lastHeartbeatRecv" : ISODate("2018-08-16T03:20:20.345Z"),
            "pingMs" : NumberLong(0),
            "configVersion" : 2
        }
    ],
    "ok" : 1.0
}

　　我们发现现在端口 27018 变成了主节点，27017 为断开状态

    4.试着关闭 27019 这个端口 然后在运行 rs.status()，结果如下

/* 1 */
{
    "set" : "haibin",
    "date" : ISODate("2018-08-16T03:21:34.102Z"),
    "myState" : 1,
    "term" : NumberLong(10),
    "heartbeatIntervalMillis" : NumberLong(2000),
    "optimes" : {
        "lastCommittedOpTime" : {
            "ts" : Timestamp(1534389603, 1),
            "t" : NumberLong(9)
        },
        "appliedOpTime" : {
            "ts" : Timestamp(1534389686, 1),
            "t" : NumberLong(10)
        },
        "durableOpTime" : {
            "ts" : Timestamp(1534389686, 1),
            "t" : NumberLong(10)
        }
    },
    "members" : [ 
        {
            "_id" : 0,
            "name" : "127.0.0.1:27017",
            "health" : 0.0,
            "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("1970-01-01T00:00:00.000Z"),
            "optimeDurableDate" : ISODate("1970-01-01T00:00:00.000Z"),
            "lastHeartbeat" : ISODate("2018-08-16T03:21:31.166Z"),
            "lastHeartbeatRecv" : ISODate("2018-08-16T03:20:02.982Z"),
            "pingMs" : NumberLong(0),
            "lastHeartbeatMessage" : "����Ŀ�������������ܾ����޷����ӡ�",
            "configVersion" : -1
        }, 
        {
            "_id" : 1,
            "name" : "127.0.0.1:27018",
            "health" : 1.0,
            "state" : 1,
            "stateStr" : "PRIMARY",
            "uptime" : 217,
            "optime" : {
                "ts" : Timestamp(1534389686, 1),
                "t" : NumberLong(10)
            },
            "optimeDate" : ISODate("2018-08-16T03:21:26.000Z"),
            "infoMessage" : "could not find member to sync from",
            "electionTime" : Timestamp(1534389614, 1),
            "electionDate" : ISODate("2018-08-16T03:20:14.000Z"),
            "configVersion" : 2,
            "self" : true
        }, 
        {
            "_id" : 2,
            "name" : "127.0.0.1:27019",
            "health" : 0.0,
            "state" : 8,
            "stateStr" : "(not reachable/healthy)",
            "uptime" : 0,
            "lastHeartbeat" : ISODate("2018-08-16T03:21:31.966Z"),
            "lastHeartbeatRecv" : ISODate("2018-08-16T03:21:25.358Z"),
            "pingMs" : NumberLong(0),
            "lastHeartbeatMessage" : "����Ŀ�������������ܾ����޷����ӡ�",
            "configVersion" : -1
        }
    ],
    "ok" : 1.0
}

　　发现现在 27018这个端口还是主节点，那么我们过一会在运行 rs.tatus(),在看下结果

/* 1 */
{
    "set" : "haibin",
    "date" : ISODate("2018-08-16T03:23:20.966Z"),
    "myState" : 2,
    "term" : NumberLong(10),
    "heartbeatIntervalMillis" : NumberLong(2000),
    "optimes" : {
        "lastCommittedOpTime" : {
            "ts" : Timestamp(1534389603, 1),
            "t" : NumberLong(9)
        },
        "appliedOpTime" : {
            "ts" : Timestamp(1534389686, 1),
            "t" : NumberLong(10)
        },
        "durableOpTime" : {
            "ts" : Timestamp(1534389686, 1),
            "t" : NumberLong(10)
        }
    },
    "members" : [ 
        {
            "_id" : 0,
            "name" : "127.0.0.1:27017",
            "health" : 0.0,
            "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("1970-01-01T00:00:00.000Z"),
            "optimeDurableDate" : ISODate("1970-01-01T00:00:00.000Z"),
            "lastHeartbeat" : ISODate("2018-08-16T03:23:20.305Z"),
            "lastHeartbeatRecv" : ISODate("2018-08-16T03:20:02.982Z"),
            "pingMs" : NumberLong(0),
            "lastHeartbeatMessage" : "����Ŀ�������������ܾ����޷����ӡ�",
            "configVersion" : -1
        }, 
        {
            "_id" : 1,
            "name" : "127.0.0.1:27018",
            "health" : 1.0,
            "state" : 2,
            "stateStr" : "SECONDARY",
            "uptime" : 323,
            "optime" : {
                "ts" : Timestamp(1534389686, 1),
                "t" : NumberLong(10)
            },
            "optimeDate" : ISODate("2018-08-16T03:21:26.000Z"),
            "infoMessage" : "could not find member to sync from",
            "configVersion" : 2,
            "self" : true
        }, 
        {
            "_id" : 2,
            "name" : "127.0.0.1:27019",
            "health" : 0.0,
            "state" : 8,
            "stateStr" : "(not reachable/healthy)",
            "uptime" : 0,
            "lastHeartbeat" : ISODate("2018-08-16T03:23:13.088Z"),
            "lastHeartbeatRecv" : ISODate("2018-08-16T03:21:25.358Z"),
            "pingMs" : NumberLong(0),
            "lastHeartbeatMessage" : "����Ŀ�������������ܾ����޷����ӡ�",
            "configVersion" : -1
        }
    ],
    "ok" : 1.0
}

　　发现此时的27018 已经不是主节点了，变成了备份节点。

经过上面的实验可以让大家知道，副本集的大多数概念，一定要记住。

最后我们再次重启一个节点（27019）过一段时间按发现 27018又变回了主节点

/* 1 */
{
    "set" : "haibin",
    "date" : ISODate("2018-08-16T03:25:34.676Z"),
    "myState" : 1,
    "term" : NumberLong(11),
    "heartbeatIntervalMillis" : NumberLong(2000),
    "optimes" : {
        "lastCommittedOpTime" : {
            "ts" : Timestamp(1534389603, 1),
            "t" : NumberLong(9)
        },
        "appliedOpTime" : {
            "ts" : Timestamp(1534389931, 1),
            "t" : NumberLong(11)
        },
        "durableOpTime" : {
            "ts" : Timestamp(1534389931, 1),
            "t" : NumberLong(11)
        }
    },
    "members" : [ 
        {
            "_id" : 0,
            "name" : "127.0.0.1:27017",
            "health" : 0.0,
            "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("1970-01-01T00:00:00.000Z"),
            "optimeDurableDate" : ISODate("1970-01-01T00:00:00.000Z"),
            "lastHeartbeat" : ISODate("2018-08-16T03:25:31.632Z"),
            "lastHeartbeatRecv" : ISODate("2018-08-16T03:20:02.982Z"),
            "pingMs" : NumberLong(0),
            "lastHeartbeatMessage" : "����Ŀ�������������ܾ����޷����ӡ�",
            "configVersion" : -1
        }, 
        {
            "_id" : 1,
            "name" : "127.0.0.1:27018",
            "health" : 1.0,
            "state" : 1,
            "stateStr" : "PRIMARY",
            "uptime" : 457,
            "optime" : {
                "ts" : Timestamp(1534389931, 1),
                "t" : NumberLong(11)
            },
            "optimeDate" : ISODate("2018-08-16T03:25:31.000Z"),
            "infoMessage" : "could not find member to sync from",
            "electionTime" : Timestamp(1534389928, 1),
            "electionDate" : ISODate("2018-08-16T03:25:28.000Z"),
            "configVersion" : 2,
            "self" : true
        }, 
        {
            "_id" : 2,
            "name" : "127.0.0.1:27019",
            "health" : 1.0,
            "state" : 7,
            "stateStr" : "ARBITER",
            "uptime" : 7,
            "lastHeartbeat" : ISODate("2018-08-16T03:25:34.640Z"),
            "lastHeartbeatRecv" : ISODate("2018-08-16T03:25:32.362Z"),
            "pingMs" : NumberLong(0),
            "configVersion" : 2
        }
    ],
    "ok" : 1.0
}

　　截取书上的文字说明，说明下为什么要使用这样的规则：