mongodb副本集原理

原理：
副本集群每2秒发一次心跳，若是10秒事后没收到则标记为不可达。
MongoDB在主数据库上应用数据库操做，而后在主数据库的操做日志中记录该操做。而后，辅助成员将这些操做复制并应用到异步过程当中。全部副本集成员在local.oplog.rs集合中都包含操做日志的副本 ，默认大小为磁盘的5%，但不记录查询操做。oplogSize能够在/etc/mongdb.conf中指定大小

replication:
oplogSizeMB: <int>
replSetName: <string>
secondaryIndexPrefetch: <string>
enableMajorityReadConcern: <boolean>

mongdb副本集中的成员:
primary: 负责写入数据
seconary: 负责同步主上的数据，提供读服务
仲裁节点： 不保有数据，不参与选主，只进行选主投票

副本集选举经过优先级，范围0-1000，0为仲裁节点，不参与选举。默认是1

如何设置？

MongoDB Enterprise shard-rs:PRIMARY> config=rs.conf()
MongoDB Enterprise shard-rs:PRIMARY> config
{
"_id" : "shard-rs",
"version" : 3,
"protocolVersion" : NumberLong(1),
"writeConcernMajorityJournalDefault" : true,
"members" : [
{
"_id" : 0,
"host" : "worker2:27020",
"arbiterOnly" : false,
"buildIndexes" : true,
"hidden" : false,
"priority" : 1,
"tags" : {

},
                    "slaveDelay" : NumberLong(0),
                    "votes" : 1
            },
            {
                    "_id" : 1,
                    "host" : "worker2:27021",
                    "arbiterOnly" : false,
                    "buildIndexes" : true,
                    "hidden" : false,
                    "priority" : 1,
                    "tags" : {

                    },
                    "slaveDelay" : NumberLong(0),
                    "votes" : 1
            },
            {
                    "_id" : 2,
                    "host" : "worker2:27022",
                    "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("5dd8bf958b8ea486b84c23b2")
    }

}

修改id值为2的分片优先级为3，当primary，则id值为2的成为prmary
config.members[2].priority=3

故意停掉27020进程
kill -9 82609

查看id值为2的主机是否成为primary
进入27022的mongdb：

MongoDB Enterprise shard-rs:PRIMARY> use adminswitched to db adminMongoDB Enterprise shard-rs:PRIMARY> db.isMaster(){"hosts" : ["worker2:27020","worker2:27021","worker2:27022"],"setName" : "shard-rs","setVersion" : 4,"ismaster" : true, # 成为primary"secondary" : false,