分佈式文檔存儲數據庫之MongoDB副本集

時間 2020-11-11

標籤 html node mysql linux web sql mongodb shell 數據庫 api 欄目系統架構简体版

原文原文鏈接

　　前文咱們聊到了mongodb的索引的相關做用和介紹以及索引的管理，回顧請參考http://www.javashuo.com/article/p-blejkthn-nu.html；今天咱們來聊下mongodb的副本集；html

　　一、什麼是副本集？主要做用是什麼？它是怎麼工做的呢？node

　　所謂副本集是指服務於同一數據集的多個mongodb實例；這意味着在mongodb中數據集副本的數量能夠是多個，每一個副本的數據都是同樣的；副本的存在主要做用是對mongodb數據庫中的數據作冗餘備份和提升數據服務的可用性；在mongodb中對數據作冗餘的方式有兩種，一種是主從架構（master/slave），這種架構和mysql中的主從架構沒有什麼不一樣，可是在mongodb中，主從架構的方式幾乎沒有人用，處於廢棄的狀態。。另一種是副本集(replica set)，副本集本質上也是主從架構的一種，它和咱們剛纔說的主從架構，有一個顯著的區別，副本集支持故障自動轉移，不須要人工手動干預；所謂的故障自動轉移是指當一個副本集中主節點因各類緣由宕機或者從節點在必定時間內沒有收到主節點發送到心跳信息，此時就會觸發從節點從新選舉主節點的操做；在多個從節點中選舉出來一個主節點之後，其餘從節點可以自動指向新選舉的主節點同步數據，從而完成此次故障轉移；mysql

　　二、mongodb副本集架構linux

　　提示：對於mongodb中的副本集來講，爲了保證數據的一致性，一個副本集中只能有一個主節點，而且只有主節點才擁有讀寫權限，其餘從節點都只有讀權限；在mongodb的副本集中，主節點咱們叫作primary，從節點叫作secondary；web

　　三、副本集是經過什麼來複制數據的呢？sql

　　我知道mysql的主從複製是經過主節點記錄寫操做到binlog中，從節點經過同步主節點的binlog，而後把同步的binlog在本地進行重放，從而實現數據同步；在mongodb中也是相似的操做，不一樣的是在mongodb中主節點將寫操做記錄到oplog(操做日誌)，各從節點經過複製主節點的oplog，在本地重放實現數據同步；oplog的做用和mysql中的binlog的做用很相似，都是用來記錄寫操做事件，都是用來同步數據；mongodb中的oplog是一個定容集合，所謂定容是指它的大小是固定的，它不會像binlog隨日誌的增多而逐漸變大；一般oplog咱們不人爲指定其大小，默認就是佔用所在文件系統空閒磁盤的5%；除了大小是不變的，它還有一個冪等的特色；所謂冪等就是無論在monogdb中執行多少次oplog中的操做，其最終的結果都是同樣的；若是寫操做日誌把oplog寫滿了，它會從頭覆蓋以前的oplog，依次循環寫oplog；mongodb

　　四、副本集是怎麼完成故障轉移的？shell

　　在前邊咱們聊zookeeper時，聊到過度布式場景中的選舉過程；mongodb的主節點故障之後，也是經過這種機制來完成選舉；在mongodb的副本集中，主節點每隔兩秒向各從節點發送心跳信息，各從節點經過檢測主節點的心跳信息來斷定主節點是否存活；若是在必定的時間範圍內，從節點沒有收到主節點發送到心跳信息，此時從節點會認爲主節點掛了，從而觸發主節點選舉的操做；這個選舉和zookeeper裏的選舉很相似，一般狀況都是大於集羣總票的一半一方能夠表明集羣正常工做；因此一般狀況mongodb副本集都是基數個節點組成；固然mongodb中也能夠是偶數節點（正常提供服務的節點），若是是偶數節點，一般會藉助一個仲裁節點來完成選舉；仲裁節點擁有選票，但不被選舉成爲主節點，也不擁有副本數據，同時它必需要可以檢測主節點心跳；簡單總結就是mongodb副本集是經過從節點檢測主節點心跳來判斷主節點是否存活，若是在必定時間範圍內，沒有檢測到主節點的心跳信息，此時就會觸發主節點選舉操做，若是集羣節點數量爲偶數個，一般會藉助仲裁節點來完成選舉；從而實現完成故障自動轉移；數據庫

　　五、mongodb副本集中特殊類型節點分類api

　　0優先級節點：這種節點的特色是優先級爲0，可參與選舉，擁有副本數據，但不被選舉成爲主節點，可讀不可寫；這種節點咱們也叫冷備節點；一般用於異地容災使用；

　　被隱藏的從節點：這種節點的特色是，可參與選舉，擁有副本數據，但不被選舉成爲主節點，對客戶端不可讀寫也不可見；一般用於同步同一副本集中的其餘節點的不一樣工做流的場景中；

　　延遲複製的從節點：這種節點的特色是，副本數據落後主節點一個時間窗口，也就說這種節點上的副本數據老是過時的；除此它可參與選舉，不可被選舉爲主節點；主要用於特殊功用；好比在主節點上執行了一個刪除操做，咱們能夠在延遲複製的從節點上把數據找回；

　　arbiter節點：這種就是咱們說的仲裁節點，它可參與選舉，不擁有副本數據，不被選舉成爲主節點，不可讀寫；主要做用是輔助斷定主節點是否存活，輔助從節點完成選舉，實現故障轉移；

　　六、建立mongodb的副本集合

　　環境準備

主機名	ip地址
node01	192.168.0.41
node02	192.168.0.42
node03	192.168.0.43

　　在三個節點上分別作好時間同步，關閉selinux,關閉防火牆，主機名解析，有必要還能夠作ssh互信。準備好基礎環境之後，在三臺server上配置mongodb的yum源

[root@node01 ~]# cat /etc/yum.repos.d/mongodb.repo 
[mongodb-org]
name = MongoDB Repository
baseurl = https://mirrors.aliyun.com/mongodb/yum/redhat/7/mongodb-org/4.4/x86_64/
gpgcheck = 1
enabled = 1
gpgkey = https://www.mongodb.org/static/pgp/server-4.4.asc
[root@node01 ~]# scp /etc/yum.repos.d/mongodb.repo node02:/etc/yum.repos.d/
mongodb.repo                                                                  100%  206    80.4KB/s   00:00    
[root@node01 ~]# scp /etc/yum.repos.d/mongodb.repo node03:/etc/yum.repos.d/
mongodb.repo                                                                  100%  206    88.9KB/s   00:00    
[root@node01 ~]#

　　安裝mongodb-org

yum install -y mongodb-org

　　準備數據目錄和存放日誌的目錄，並將其屬主和屬組更改成mongod用戶

[root@node01 ~]# mkdir -pv /mongodb/{data,log} 
mkdir: created directory ‘/mongodb’
mkdir: created directory ‘/mongodb/data’
mkdir: created directory ‘/mongodb/log’
[root@node01 ~]# chown -R mongod.mongod /mongodb/
[root@node01 ~]# ll -d /mongodb/
drwxr-xr-x 4 mongod mongod 29 Nov 10 19:36 /mongodb/
[root@node01 ~]#

　　提示：以上需在三個節點都要作一遍；

　　配置mongodb

　　提示：主要配置replication，其中oplogSizeMB用來指定oplog的大小，默認不指定，其大小就是所在文件系統空閒磁盤的%5；replSetName用來指定副本集的名稱，這個名稱很是重要，主要用來標識不一樣副本集；enableMajorityReadConcern用來指定是否開啓mongodb週期性的作快照，並記錄oplog的時間戳；

　　完整配置

[root@node01 ~]# cat /etc/mongod.conf
systemLog:
  destination: file
  logAppend: true
  path: /mongodb/log/mongod.log

storage:
  dbPath: /mongodb/data/
  journal:
    enabled: true

processManagement:
  fork: true  
  pidFilePath: /var/run/mongodb/mongod.pid
  timeZoneInfo: /usr/share/zoneinfo

net:
  port: 27017
  bindIp: 0.0.0.0

replication:
   oplogSizeMB: 2048
   replSetName: test_replset
   enableMajorityReadConcern: false



#security:

#operationProfiling:

#sharding:

## Enterprise-Only Options

#auditLog:

#snmp:
[root@node01 ~]#

View Code

　　複製配置文件到node02,node03

[root@node01 ~]# scp /etc/mongod.conf node02:/etc/
mongod.conf                                                                   100%  494   315.1KB/s   00:00    
[root@node01 ~]# scp /etc/mongod.conf node03:/etc/
mongod.conf                                                                   100%  494   351.6KB/s   00:00    
[root@node01 ~]#

　　啓動服務

　　提示：請確保對應節點上的mongodb所監聽的端口正常便可；

　　鏈接三個節點任意一個節點查看副本集狀態

> rs.help()
        rs.status()                                { replSetGetStatus : 1 } checks repl set status
        rs.initiate()                              { replSetInitiate : null } initiates set with default settings
        rs.initiate(cfg)                           { replSetInitiate : cfg } initiates set with configuration cfg
        rs.conf()                                  get the current configuration object from local.system.replset
        rs.reconfig(cfg)                           updates the configuration of a running replica set with cfg (disconnects)
        rs.add(hostportstr)                        add a new member to the set with default attributes (disconnects)
        rs.add(membercfgobj)                       add a new member to the set with extra attributes (disconnects)
        rs.addArb(hostportstr)                     add a new member which is arbiterOnly:true (disconnects)
        rs.stepDown([stepdownSecs, catchUpSecs])   step down as primary (disconnects)
        rs.syncFrom(hostportstr)                   make a secondary sync from the given member
        rs.freeze(secs)                            make a node ineligible to become primary for the time specified
        rs.remove(hostportstr)                     remove a host from the replica set (disconnects)
        rs.secondaryOk()                               allow queries on secondary nodes

        rs.printReplicationInfo()                  check oplog size and time range
        rs.printSecondaryReplicationInfo()             check replica set members and replication lag
        db.isMaster()                              check who is primary

        reconfiguration helpers disconnect from the database so the shell will display
        an error, even if the command succeeds.
> rs.status() 
{
        "operationTime" : Timestamp(0, 0),
        "ok" : 0,
        "errmsg" : "no replset config has been received",
        "code" : 94,
        "codeName" : "NotYetInitialized",
        "$clusterTime" : {
                "clusterTime" : Timestamp(0, 0),
                "signature" : {
                        "hash" : BinData(0,"AAAAAAAAAAAAAAAAAAAAAAAAAAA="),
                        "keyId" : NumberLong(0)
                }
        }
}
>

　　提示：全部關於副本集的操做命令均可以使用rs.help()方法去查看幫助；其中rs.status()是用來查看副本集狀態；這裏顯示沒有副本集配置，其緣由是沒有初始化副本集；

　　初始化副本集

> rs.initiate()
{
        "info2" : "no configuration specified. Using a default configuration for the set",
        "me" : "node01.test.org:27017",
        "ok" : 1,
        "$clusterTime" : {
                "clusterTime" : Timestamp(1605010821, 1),
                "signature" : {
                        "hash" : BinData(0,"AAAAAAAAAAAAAAAAAAAAAAAAAAA="),
                        "keyId" : NumberLong(0)
                }
        },
        "operationTime" : Timestamp(1605010821, 1)
}
test_replset:SECONDARY> rs.status()
{
        "set" : "test_replset",
        "date" : ISODate("2020-11-10T12:20:32.079Z"),
        "myState" : 1,
        "term" : NumberLong(1),
        "syncSourceHost" : "",
        "syncSourceId" : -1,
        "heartbeatIntervalMillis" : NumberLong(2000),
        "majorityVoteCount" : 1,
        "writeMajorityCount" : 1,
        "votingMembersCount" : 1,
        "writableVotingMembersCount" : 1,
        "optimes" : {
                "lastCommittedOpTime" : {
                        "ts" : Timestamp(1605010821, 8),
                        "t" : NumberLong(1)
                },
                "lastCommittedWallTime" : ISODate("2020-11-10T12:20:21.720Z"),
                "readConcernMajorityOpTime" : {
                        "ts" : Timestamp(1605010821, 8),
                        "t" : NumberLong(1)
                },
                "readConcernMajorityWallTime" : ISODate("2020-11-10T12:20:21.720Z"),
                "appliedOpTime" : {
                        "ts" : Timestamp(1605010821, 8),
                        "t" : NumberLong(1)
                },
                "durableOpTime" : {
                        "ts" : Timestamp(1605010821, 8),
                        "t" : NumberLong(1)
                },
                "lastAppliedWallTime" : ISODate("2020-11-10T12:20:21.720Z"),
                "lastDurableWallTime" : ISODate("2020-11-10T12:20:21.720Z")
        },
        "electionCandidateMetrics" : {
                "lastElectionReason" : "electionTimeout",
                "lastElectionDate" : ISODate("2020-11-10T12:20:21.632Z"),
                "electionTerm" : NumberLong(1),
                "lastCommittedOpTimeAtElection" : {
                        "ts" : Timestamp(0, 0),
                        "t" : NumberLong(-1)
                },
                "lastSeenOpTimeAtElection" : {
                        "ts" : Timestamp(1605010821, 1),
                        "t" : NumberLong(-1)
                },
                "numVotesNeeded" : 1,
                "priorityAtElection" : 1,
                "electionTimeoutMillis" : NumberLong(10000),
                "newTermStartDate" : ISODate("2020-11-10T12:20:21.694Z"),
                "wMajorityWriteAvailabilityDate" : ISODate("2020-11-10T12:20:21.719Z")
        },
        "members" : [
                {
                        "_id" : 0,
                        "name" : "node01.test.org:27017",
                        "health" : 1,
                        "state" : 1,
                        "stateStr" : "PRIMARY",
                        "uptime" : 674,
                        "optime" : {
                                "ts" : Timestamp(1605010821, 8),
                                "t" : NumberLong(1)
                        },
                        "optimeDate" : ISODate("2020-11-10T12:20:21Z"),
                        "syncSourceHost" : "",
                        "syncSourceId" : -1,
                        "infoMessage" : "Could not find member to sync from",
                        "electionTime" : Timestamp(1605010821, 2),
                        "electionDate" : ISODate("2020-11-10T12:20:21Z"),
                        "configVersion" : 1,
                        "configTerm" : 1,
                        "self" : true,
                        "lastHeartbeatMessage" : ""
                }
        ],
        "ok" : 1,
        "$clusterTime" : {
                "clusterTime" : Timestamp(1605010821, 8),
                "signature" : {
                        "hash" : BinData(0,"AAAAAAAAAAAAAAAAAAAAAAAAAAA="),
                        "keyId" : NumberLong(0)
                }
        },
        "operationTime" : Timestamp(1605010821, 8)
}
test_replset:PRIMARY>

　　提示：初始化副本集之後，再次查看副本集狀態，它告訴咱們有一個成員，其主機名爲node01.test.org:27017,其health狀態爲1，stateStr爲PRIMARY等等一堆信息；

　　查看副本集配置

test_replset:PRIMARY> rs.conf()
{
        "_id" : "test_replset",
        "version" : 1,
        "term" : 1,
        "protocolVersion" : NumberLong(1),
        "writeConcernMajorityJournalDefault" : true,
        "members" : [
                {
                        "_id" : 0,
                        "host" : "node01.test.org:27017",
                        "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("5faa85853d5a2d8fdf8af85e")
        }
}
test_replset:PRIMARY>

　　提示：能夠看到心跳時間間隔爲2s，超時爲10s,選舉超時時長爲10等等信息；

　　添加node02，node03節點到副本集成員

test_replset:PRIMARY> rs.add("node02")
{
        "ok" : 1,
        "$clusterTime" : {
                "clusterTime" : Timestamp(1605011243, 1),
                "signature" : {
                        "hash" : BinData(0,"AAAAAAAAAAAAAAAAAAAAAAAAAAA="),
                        "keyId" : NumberLong(0)
                }
        },
        "operationTime" : Timestamp(1605011243, 1)
}
test_replset:PRIMARY> rs.add("node03")
{
        "ok" : 1,
        "$clusterTime" : {
                "clusterTime" : Timestamp(1605011250, 1),
                "signature" : {
                        "hash" : BinData(0,"AAAAAAAAAAAAAAAAAAAAAAAAAAA="),
                        "keyId" : NumberLong(0)
                }
        },
        "operationTime" : Timestamp(1605011250, 1)
}
test_replset:PRIMARY> rs.status()
{
        "set" : "test_replset",
        "date" : ISODate("2020-11-10T12:27:45.849Z"),
        "myState" : 1,
        "term" : NumberLong(1),
        "syncSourceHost" : "",
        "syncSourceId" : -1,
        "heartbeatIntervalMillis" : NumberLong(2000),
        "majorityVoteCount" : 2,
        "writeMajorityCount" : 2,
        "votingMembersCount" : 3,
        "writableVotingMembersCount" : 3,
        "optimes" : {
                "lastCommittedOpTime" : {
                        "ts" : Timestamp(1605011261, 1),
                        "t" : NumberLong(1)
                },
                "lastCommittedWallTime" : ISODate("2020-11-10T12:27:41.873Z"),
                "readConcernMajorityOpTime" : {
                        "ts" : Timestamp(1605011261, 1),
                        "t" : NumberLong(1)
                },
                "readConcernMajorityWallTime" : ISODate("2020-11-10T12:27:41.873Z"),
                "appliedOpTime" : {
                        "ts" : Timestamp(1605011261, 1),
                        "t" : NumberLong(1)
                },
                "durableOpTime" : {
                        "ts" : Timestamp(1605011261, 1),
                        "t" : NumberLong(1)
                },
                "lastAppliedWallTime" : ISODate("2020-11-10T12:27:41.873Z"),
                "lastDurableWallTime" : ISODate("2020-11-10T12:27:41.873Z")
        },
        "electionCandidateMetrics" : {
                "lastElectionReason" : "electionTimeout",
                "lastElectionDate" : ISODate("2020-11-10T12:20:21.632Z"),
                "electionTerm" : NumberLong(1),
                "lastCommittedOpTimeAtElection" : {
                        "ts" : Timestamp(0, 0),
                        "t" : NumberLong(-1)
                },
                "lastSeenOpTimeAtElection" : {
                        "ts" : Timestamp(1605010821, 1),
                        "t" : NumberLong(-1)
                },
                "numVotesNeeded" : 1,
                "priorityAtElection" : 1,
                "electionTimeoutMillis" : NumberLong(10000),
                "newTermStartDate" : ISODate("2020-11-10T12:20:21.694Z"),
                "wMajorityWriteAvailabilityDate" : ISODate("2020-11-10T12:20:21.719Z")
        },
        "members" : [
                {
                        "_id" : 0,
                        "name" : "node01.test.org:27017",
                        "health" : 1,
                        "state" : 1,
                        "stateStr" : "PRIMARY",
                        "uptime" : 1107,
                        "optime" : {
                                "ts" : Timestamp(1605011261, 1),
                                "t" : NumberLong(1)
                        },
                        "optimeDate" : ISODate("2020-11-10T12:27:41Z"),
                        "syncSourceHost" : "",
                        "syncSourceId" : -1,
                        "infoMessage" : "",
                        "electionTime" : Timestamp(1605010821, 2),
                        "electionDate" : ISODate("2020-11-10T12:20:21Z"),
                        "configVersion" : 3,
                        "configTerm" : 1,
                        "self" : true,
                        "lastHeartbeatMessage" : ""
                },
                {
                        "_id" : 1,
                        "name" : "node02:27017",
                        "health" : 1,
                        "state" : 2,
                        "stateStr" : "SECONDARY",
                        "uptime" : 21,
                        "optime" : {
                                "ts" : Timestamp(1605011261, 1),
                                "t" : NumberLong(1)
                        },
                        "optimeDurable" : {
                                "ts" : Timestamp(1605011261, 1),
                                "t" : NumberLong(1)
                        },
                        "optimeDate" : ISODate("2020-11-10T12:27:41Z"),
                        "optimeDurableDate" : ISODate("2020-11-10T12:27:41Z"),
                        "lastHeartbeat" : ISODate("2020-11-10T12:27:44.967Z"),
                        "lastHeartbeatRecv" : ISODate("2020-11-10T12:27:43.983Z"),
                        "pingMs" : NumberLong(0),
                        "lastHeartbeatMessage" : "",
                        "syncSourceHost" : "node01.test.org:27017",
                        "syncSourceId" : 0,
                        "infoMessage" : "",
                        "configVersion" : 3,
                        "configTerm" : 1
                },
                {
                        "_id" : 2,
                        "name" : "node03:27017",
                        "health" : 1,
                        "state" : 2,
                        "stateStr" : "SECONDARY",
                        "uptime" : 14,
                        "optime" : {
                                "ts" : Timestamp(1605011261, 1),
                                "t" : NumberLong(1)
                        },
                        "optimeDurable" : {
                                "ts" : Timestamp(1605011261, 1),
                                "t" : NumberLong(1)
                        },
                        "optimeDate" : ISODate("2020-11-10T12:27:41Z"),
                        "optimeDurableDate" : ISODate("2020-11-10T12:27:41Z"),
                        "lastHeartbeat" : ISODate("2020-11-10T12:27:44.967Z"),
                        "lastHeartbeatRecv" : ISODate("2020-11-10T12:27:44.571Z"),
                        "pingMs" : NumberLong(1),
                        "lastHeartbeatMessage" : "",
                        "syncSourceHost" : "node02:27017",
                        "syncSourceId" : 1,
                        "infoMessage" : "",
                        "configVersion" : 3,
                        "configTerm" : 1
                }
        ],
        "ok" : 1,
        "$clusterTime" : {
                "clusterTime" : Timestamp(1605011261, 1),
                "signature" : {
                        "hash" : BinData(0,"AAAAAAAAAAAAAAAAAAAAAAAAAAA="),
                        "keyId" : NumberLong(0)
                }
        },
        "operationTime" : Timestamp(1605011261, 1)
}
test_replset:PRIMARY>

　　提示：添加節點到副本成員使用rs.add（），括號裏面寫主機名，或者ip地址，若是對應節點監聽端口不是27017，還須要寫明端口；除此咱們也能夠直接用一個子文檔的形式，手動指定節點的各屬性信息來添加節點到副本集成員；

　　到此副本集的配置就完成了，三個節點都添加到副本集；

　　驗證：在主庫上插入數據，看看從庫是否均可以正常同步其數據呢？

　　在主節點插入數據

test_replset:PRIMARY> use students
switched to db students
test_replset:PRIMARY> db.student_info.insert({name:"tom",age:18,gender:"M"})
WriteResult({ "nInserted" : 1 })
test_replset:PRIMARY> db.student_info.find()
{ "_id" : ObjectId("5faa89297077300f4fc31d1c"), "name" : "tom", "age" : 18, "gender" : "M" }
test_replset:PRIMARY>

　　在從節點查看數據

test_replset:SECONDARY> show dbs
uncaught exception: Error: listDatabases failed:{
        "topologyVersion" : {
                "processId" : ObjectId("5faa83025f9218c5d19ea91b"),
                "counter" : NumberLong(4)
        },
        "operationTime" : Timestamp(1605011801, 1),
        "ok" : 0,
        "errmsg" : "not master and slaveOk=false",
        "code" : 13435,
        "codeName" : "NotMasterNoSlaveOk",
        "$clusterTime" : {
                "clusterTime" : Timestamp(1605011801, 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:147:19
Mongo.prototype.getDBs@src/mongo/shell/mongo.js:99:12
shellHelper.show@src/mongo/shell/utils.js:937:13
shellHelper@src/mongo/shell/utils.js:819:15
@(shellhelp2):1:1
test_replset:SECONDARY>

　　提示：這裏在從節點上無法查看數據，緣由是默認狀況副本集配置好之後，要在從節點運行rs.secondaryOk()來告訴從節點已經配置好了，不然它會不容許咱們讀，有點相似從節點爲就緒的感受；

　　在從節點上運行rs.secondaryOk(),而後再次查看數據

test_replset:SECONDARY> rs.secondaryOk()  
test_replset:SECONDARY> show dbs
admin     0.000GB
config    0.000GB
local     0.000GB
students  0.000GB
test_replset:SECONDARY> use students
switched to db students
test_replset:SECONDARY> show collections
student_info
test_replset:SECONDARY> db.student_info.find().pretty()
{
        "_id" : ObjectId("5faa89297077300f4fc31d1c"),
        "name" : "tom",
        "age" : 18,
        "gender" : "M"
}
test_replset:SECONDARY>

　　提示：能夠看到在secondary節點上可以查詢到對應數據庫中的對應collection中插入的數據；

　　驗證：在從節點上插入數據，看看是否能插入成功？

test_replset:SECONDARY> db.student_info.insert({name:"jerry",age:19,gender:"M"})
WriteCommandError({
        "topologyVersion" : {
                "processId" : ObjectId("5faa831bde03c4ae108f0be4"),
                "counter" : NumberLong(3)
        },
        "operationTime" : Timestamp(1605012904, 1),
        "ok" : 0,
        "errmsg" : "not master",
        "code" : 10107,
        "codeName" : "NotMaster",
        "$clusterTime" : {
                "clusterTime" : Timestamp(1605012904, 1),
                "signature" : {
                        "hash" : BinData(0,"AAAAAAAAAAAAAAAAAAAAAAAAAAA="),
                        "keyId" : NumberLong(0)
                }
        }
})
test_replset:SECONDARY>

　　提示：咱們在從節點上插入數據，它提示咱們不是主節點，不容許插入數據；這說明副本集的從節點是不容許寫；

　　驗證：將主節點上的mongodb服務停掉，而後在其餘兩個節點上查看副本集狀態，看看兩個節點是否從新選舉了master?

[root@node01 ~]# systemctl stop mongod.service 
[root@node01 ~]# ss -tnl
State      Recv-Q Send-Q           Local Address:Port                          Peer Address:Port              
LISTEN     0      128                          *:22                                       *:*                  
LISTEN     0      100                  127.0.0.1:25                                       *:*                  
LISTEN     0      128                         :::22                                      :::*                  
LISTEN     0      100                        ::1:25                                      :::*                  
[root@node01 ~]# mongo --host node02
MongoDB shell version v4.4.1
connecting to: mongodb://node02:27017/?compressors=disabled&gssapiServiceName=mongodb
Implicit session: session { "id" : UUID("90d60f76-fc95-44a8-bbf7-d927d5947331") }
MongoDB server version: 4.4.1
---
The server generated these startup warnings when booting: 
        2020-11-10T20:09:39.555+08:00: Access control is not enabled for the database. Read and write access to data and configuration is unrestricted
        2020-11-10T20:09:39.555+08:00: /sys/kernel/mm/transparent_hugepage/enabled is 'always'. We suggest setting it to 'never'
        2020-11-10T20:09:39.555+08:00: /sys/kernel/mm/transparent_hugepage/defrag is 'always'. We suggest setting it to 'never'
---
---
        Enable MongoDB's free cloud-based monitoring service, which will then receive and display
        metrics about your deployment (disk utilization, CPU, operation statistics, etc).

        The monitoring data will be available on a MongoDB website with a unique URL accessible to you
        and anyone you share the URL with. MongoDB may use this information to make product
        improvements and to suggest MongoDB products and deployment options to you.

        To enable free monitoring, run the following command: db.enableFreeMonitoring()
        To permanently disable this reminder, run the following command: db.disableFreeMonitoring()
---
test_replset:PRIMARY> rs.status()
{
        "set" : "test_replset",
        "date" : ISODate("2020-11-10T12:59:25.775Z"),
        "myState" : 1,
        "term" : NumberLong(2),
        "syncSourceHost" : "",
        "syncSourceId" : -1,
        "heartbeatIntervalMillis" : NumberLong(2000),
        "majorityVoteCount" : 2,
        "writeMajorityCount" : 2,
        "votingMembersCount" : 3,
        "writableVotingMembersCount" : 3,
        "optimes" : {
                "lastCommittedOpTime" : {
                        "ts" : Timestamp(1605013164, 1),
                        "t" : NumberLong(2)
                },
                "lastCommittedWallTime" : ISODate("2020-11-10T12:59:24.417Z"),
                "readConcernMajorityOpTime" : {
                        "ts" : Timestamp(1605013164, 1),
                        "t" : NumberLong(2)
                },
                "readConcernMajorityWallTime" : ISODate("2020-11-10T12:59:24.417Z"),
                "appliedOpTime" : {
                        "ts" : Timestamp(1605013164, 1),
                        "t" : NumberLong(2)
                },
                "durableOpTime" : {
                        "ts" : Timestamp(1605013164, 1),
                        "t" : NumberLong(2)
                },
                "lastAppliedWallTime" : ISODate("2020-11-10T12:59:24.417Z"),
                "lastDurableWallTime" : ISODate("2020-11-10T12:59:24.417Z")
        },
        "electionCandidateMetrics" : {
                "lastElectionReason" : "stepUpRequestSkipDryRun",
                "lastElectionDate" : ISODate("2020-11-10T12:58:34.398Z"),
                "electionTerm" : NumberLong(2),
                "lastCommittedOpTimeAtElection" : {
                        "ts" : Timestamp(1605013112, 1),
                        "t" : NumberLong(1)
                },
                "lastSeenOpTimeAtElection" : {
                        "ts" : Timestamp(1605013112, 1),
                        "t" : NumberLong(1)
                },
                "numVotesNeeded" : 2,
                "priorityAtElection" : 1,
                "electionTimeoutMillis" : NumberLong(10000),
                "priorPrimaryMemberId" : 0,
                "numCatchUpOps" : NumberLong(0),
                "newTermStartDate" : ISODate("2020-11-10T12:58:34.410Z"),
                "wMajorityWriteAvailabilityDate" : ISODate("2020-11-10T12:58:34.506Z")
        },
        "members" : [
                {
                        "_id" : 0,
                        "name" : "node01.test.org:27017",
                        "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("2020-11-10T12:59:24.558Z"),
                        "lastHeartbeatRecv" : ISODate("2020-11-10T12:58:35.045Z"),
                        "pingMs" : NumberLong(0),
                        "lastHeartbeatMessage" : "Error connecting to node01.test.org:27017 (192.168.0.41:27017) :: caused by :: Connection refused",
                        "syncSourceHost" : "",
                        "syncSourceId" : -1,
                        "infoMessage" : "",
                        "configVersion" : 3,
                        "configTerm" : 1
                },
                {
                        "_id" : 1,
                        "name" : "node02:27017",
                        "health" : 1,
                        "state" : 1,
                        "stateStr" : "PRIMARY",
                        "uptime" : 2987,
                        "optime" : {
                                "ts" : Timestamp(1605013164, 1),
                                "t" : NumberLong(2)
                        },
                        "optimeDate" : ISODate("2020-11-10T12:59:24Z"),
                        "syncSourceHost" : "",
                        "syncSourceId" : -1,
                        "infoMessage" : "",
                        "electionTime" : Timestamp(1605013114, 1),
                        "electionDate" : ISODate("2020-11-10T12:58:34Z"),
                        "configVersion" : 3,
                        "configTerm" : 2,
                        "self" : true,
                        "lastHeartbeatMessage" : ""
                },
                {
                        "_id" : 2,
                        "name" : "node03:27017",
                        "health" : 1,
                        "state" : 2,
                        "stateStr" : "SECONDARY",
                        "uptime" : 1914,
                        "optime" : {
                                "ts" : Timestamp(1605013164, 1),
                                "t" : NumberLong(2)
                        },
                        "optimeDurable" : {
                                "ts" : Timestamp(1605013164, 1),
                                "t" : NumberLong(2)
                        },
                        "optimeDate" : ISODate("2020-11-10T12:59:24Z"),
                        "optimeDurableDate" : ISODate("2020-11-10T12:59:24Z"),
                        "lastHeartbeat" : ISODate("2020-11-10T12:59:24.459Z"),
                        "lastHeartbeatRecv" : ISODate("2020-11-10T12:59:25.506Z"),
                        "pingMs" : NumberLong(0),
                        "lastHeartbeatMessage" : "",
                        "syncSourceHost" : "node02:27017",
                        "syncSourceId" : 1,
                        "infoMessage" : "",
                        "configVersion" : 3,
                        "configTerm" : 2
                }
        ],
        "ok" : 1,
        "$clusterTime" : {
                "clusterTime" : Timestamp(1605013164, 1),
                "signature" : {
                        "hash" : BinData(0,"AAAAAAAAAAAAAAAAAAAAAAAAAAA="),
                        "keyId" : NumberLong(0)
                }
        },
        "operationTime" : Timestamp(1605013164, 1)
}
test_replset:PRIMARY>

　　提示：能夠看到當node01上的mongodb服務停掉之後，對應的主節點也就不可以正常的向從節點發送心跳，因此剩下的兩個從節點都認爲主節點掛了，此時他倆就開始從新選舉主節點；咱們再次鏈接到node02上的mongodb查看副本集狀態時，此時node02上的mongodb就成爲了主節點；同時咱們也能看到node01的健康狀態爲0，表示不健康；

　　查看從節點的複製信息

test_replset:PRIMARY> rs.printSecondaryReplicationInfo()
source: node01.test.org:27017
        syncedTo: Thu Jan 01 1970 08:00:00 GMT+0800 (CST)
        1605013534 secs (445837.09 hrs) behind the primary 
source: node03:27017
        syncedTo: Tue Nov 10 2020 21:05:34 GMT+0800 (CST)
        0 secs (0 hrs) behind the primary 
test_replset:PRIMARY>

　　提示：這裏能夠看到node01落後主節點很長時間，node03不落後主節點；

　　查看同步信息時間窗口，以及oplog大小

test_replset:PRIMARY> rs.printReplicationInfo()
configured oplog size:   2048MB
log length start to end: 2291secs (0.64hrs)
oplog first event time:  Tue Nov 10 2020 20:27:23 GMT+0800 (CST)
oplog last event time:   Tue Nov 10 2020 21:05:34 GMT+0800 (CST)
now:                     Tue Nov 10 2020 21:05:35 GMT+0800 (CST)
test_replset:PRIMARY>

　　提示：能夠看到oplog的小爲2048MB，日誌開始到結束的時間窗口爲2291秒，意思是說當前啓動副本集到查詢複製信息是的時長爲2291秒；第一個oplog時間時間和最後oplog事件時間以及如今的時間均可查看獲得；

　　移除節點（從副本集中，將node01節點移除）

test_replset:PRIMARY> rs.remove("node01.test.org:27017")
{
        "ok" : 1,
        "$clusterTime" : {
                "clusterTime" : Timestamp(1605014063, 1),
                "signature" : {
                        "hash" : BinData(0,"AAAAAAAAAAAAAAAAAAAAAAAAAAA="),
                        "keyId" : NumberLong(0)
                }
        },
        "operationTime" : Timestamp(1605014063, 1)
}
test_replset:PRIMARY> rs.status()
{
        "set" : "test_replset",
        "date" : ISODate("2020-11-10T13:14:35.362Z"),
        "myState" : 1,
        "term" : NumberLong(2),
        "syncSourceHost" : "",
        "syncSourceId" : -1,
        "heartbeatIntervalMillis" : NumberLong(2000),
        "majorityVoteCount" : 2,
        "writeMajorityCount" : 2,
        "votingMembersCount" : 2,
        "writableVotingMembersCount" : 2,
        "optimes" : {
                "lastCommittedOpTime" : {
                        "ts" : Timestamp(1605014074, 1),
                        "t" : NumberLong(2)
                },
                "lastCommittedWallTime" : ISODate("2020-11-10T13:14:34.514Z"),
                "readConcernMajorityOpTime" : {
                        "ts" : Timestamp(1605014074, 1),
                        "t" : NumberLong(2)
                },
                "readConcernMajorityWallTime" : ISODate("2020-11-10T13:14:34.514Z"),
                "appliedOpTime" : {
                        "ts" : Timestamp(1605014074, 1),
                        "t" : NumberLong(2)
                },
                "durableOpTime" : {
                        "ts" : Timestamp(1605014074, 1),
                        "t" : NumberLong(2)
                },
                "lastAppliedWallTime" : ISODate("2020-11-10T13:14:34.514Z"),
                "lastDurableWallTime" : ISODate("2020-11-10T13:14:34.514Z")
        },
        "electionCandidateMetrics" : {
                "lastElectionReason" : "stepUpRequestSkipDryRun",
                "lastElectionDate" : ISODate("2020-11-10T12:58:34.398Z"),
                "electionTerm" : NumberLong(2),
                "lastCommittedOpTimeAtElection" : {
                        "ts" : Timestamp(1605013112, 1),
                        "t" : NumberLong(1)
                },
                "lastSeenOpTimeAtElection" : {
                        "ts" : Timestamp(1605013112, 1),
                        "t" : NumberLong(1)
                },
                "numVotesNeeded" : 2,
                "priorityAtElection" : 1,
                "electionTimeoutMillis" : NumberLong(10000),
                "priorPrimaryMemberId" : 0,
                "numCatchUpOps" : NumberLong(0),
                "newTermStartDate" : ISODate("2020-11-10T12:58:34.410Z"),
                "wMajorityWriteAvailabilityDate" : ISODate("2020-11-10T12:58:34.506Z")
        },
        "members" : [
                {
                        "_id" : 1,
                        "name" : "node02:27017",
                        "health" : 1,
                        "state" : 1,
                        "stateStr" : "PRIMARY",
                        "uptime" : 3897,
                        "optime" : {
                                "ts" : Timestamp(1605014074, 1),
                                "t" : NumberLong(2)
                        },
                        "optimeDate" : ISODate("2020-11-10T13:14:34Z"),
                        "syncSourceHost" : "",
                        "syncSourceId" : -1,
                        "infoMessage" : "",
                        "electionTime" : Timestamp(1605013114, 1),
                        "electionDate" : ISODate("2020-11-10T12:58:34Z"),
                        "configVersion" : 4,
                        "configTerm" : 2,
                        "self" : true,
                        "lastHeartbeatMessage" : ""
                },
                {
                        "_id" : 2,
                        "name" : "node03:27017",
                        "health" : 1,
                        "state" : 2,
                        "stateStr" : "SECONDARY",
                        "uptime" : 2824,
                        "optime" : {
                                "ts" : Timestamp(1605014063, 1),
                                "t" : NumberLong(2)
                        },
                        "optimeDurable" : {
                                "ts" : Timestamp(1605014063, 1),
                                "t" : NumberLong(2)
                        },
                        "optimeDate" : ISODate("2020-11-10T13:14:23Z"),
                        "optimeDurableDate" : ISODate("2020-11-10T13:14:23Z"),
                        "lastHeartbeat" : ISODate("2020-11-10T13:14:33.958Z"),
                        "lastHeartbeatRecv" : ISODate("2020-11-10T13:14:33.970Z"),
                        "pingMs" : NumberLong(0),
                        "lastHeartbeatMessage" : "",
                        "syncSourceHost" : "node02:27017",
                        "syncSourceId" : 1,
                        "infoMessage" : "",
                        "configVersion" : 4,
                        "configTerm" : 2
                }
        ],
        "ok" : 1,
        "$clusterTime" : {
                "clusterTime" : Timestamp(1605014074, 1),
                "signature" : {
                        "hash" : BinData(0,"AAAAAAAAAAAAAAAAAAAAAAAAAAA="),
                        "keyId" : NumberLong(0)
                }
        },
        "operationTime" : Timestamp(1605014074, 1)
}
test_replset:PRIMARY>

　　提示：移除節點須要寫明對應節點的主機名地址和端口，或者是ip地址端口；這個字串必須是同加入到副本集中的名字相同纔可移除，不然它會提示咱們給定主機字符串找不到；

　　設置node03的優先級爲10

test_replset:PRIMARY> cfg = rs.conf()
{
        "_id" : "test_replset",
        "version" : 4,
        "term" : 2,
        "protocolVersion" : NumberLong(1),
        "writeConcernMajorityJournalDefault" : true,
        "members" : [
                {
                        "_id" : 1,
                        "host" : "node02:27017",
                        "arbiterOnly" : false,
                        "buildIndexes" : true,
                        "hidden" : false,
                        "priority" : 1,
                        "tags" : {

                        },
                        "slaveDelay" : NumberLong(0),
                        "votes" : 1
                },
                {
                        "_id" : 2,
                        "host" : "node03:27017",
                        "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("5faa85853d5a2d8fdf8af85e")
        }
}
test_replset:PRIMARY> cfg.members[1].priority = 10
10
test_replset:PRIMARY> rs.reconfig(cfg)
{
        "ok" : 1,
        "$clusterTime" : {
                "clusterTime" : Timestamp(1605015945, 1),
                "signature" : {
                        "hash" : BinData(0,"AAAAAAAAAAAAAAAAAAAAAAAAAAA="),
                        "keyId" : NumberLong(0)
                }
        },
        "operationTime" : Timestamp(1605015945, 1)
}
test_replset:PRIMARY> rs.config()
{
        "_id" : "test_replset",
        "version" : 5,
        "term" : 3,
        "protocolVersion" : NumberLong(1),
        "writeConcernMajorityJournalDefault" : true,
        "members" : [
                {
                        "_id" : 1,
                        "host" : "node02:27017",
                        "arbiterOnly" : false,
                        "buildIndexes" : true,
                        "hidden" : false,
                        "priority" : 1,
                        "tags" : {

                        },
                        "slaveDelay" : NumberLong(0),
                        "votes" : 1
                },
                {
                        "_id" : 2,
                        "host" : "node03:27017",
                        "arbiterOnly" : false,
                        "buildIndexes" : true,
                        "hidden" : false,
                        "priority" : 10,
                        "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("5faa85853d5a2d8fdf8af85e")
        }
}
test_replset:SECONDARY>

　　提示：設置某個成員的優先級，首先要把當前配置用一個變量保存，而後經過修改保存的配置變量來修改優先級之後，再使用rs.reconfig()來讀取修改後的配置便可生效；這裏須要注意我在修改配置文件時指定成員，是指定對應成員在members列表的下標，而非id；因此修改前要先肯定對應成員的下標是多少；咱們修改了node03的優先級之後，心細的你必定會發現node02此時就變成了secondary;這意味着，只要在副本集中有更高優先級的成員加入，會觸發一次選舉，固然選舉成爲主節點，影響最大的就是各節點的優先級，優先級越高，當選主節點的概率就越大；默認狀況每一個成員的優先級都爲1，優先級設定的取值範圍是0-1000；

　　將node01上的mongodb服務啓動起來，而後在主節點上將其添加爲仲裁節點

　　啓動node01上的mongodb服務

[root@node01 ~]# systemctl start mongod.service 
[root@node01 ~]# ss -tnl
State      Recv-Q Send-Q           Local Address:Port                          Peer Address:Port              
LISTEN     0      128                          *:22                                       *:*                  
LISTEN     0      100                  127.0.0.1:25                                       *:*                  
LISTEN     0      128                          *:27017                                    *:*                  
LISTEN     0      128                         :::22                                      :::*                  
LISTEN     0      100                        ::1:25                                      :::*                  
[root@node01 ~]#

　　在主節點上將node01添加爲仲裁節點

test_replset:PRIMARY> rs.addArb("node01")
{
        "ok" : 1,
        "$clusterTime" : {
                "clusterTime" : Timestamp(1605016848, 1),
                "signature" : {
                        "hash" : BinData(0,"AAAAAAAAAAAAAAAAAAAAAAAAAAA="),
                        "keyId" : NumberLong(0)
                }
        },
        "operationTime" : Timestamp(1605016848, 1)
}
test_replset:PRIMARY>

　　查看配置信息，看看node01上的arbiterOnly是否變成了true?

test_replset:PRIMARY> rs.config()
{
        "_id" : "test_replset",
        "version" : 8,
        "term" : 3,
        "protocolVersion" : NumberLong(1),
        "writeConcernMajorityJournalDefault" : true,
        "members" : [
                {
                        "_id" : 1,
                        "host" : "node02:27017",
                        "arbiterOnly" : false,
                        "buildIndexes" : true,
                        "hidden" : false,
                        "priority" : 1,
                        "tags" : {

                        },
                        "slaveDelay" : NumberLong(0),
                        "votes" : 1
                },
                {
                        "_id" : 2,
                        "host" : "node03:27017",
                        "arbiterOnly" : false,
                        "buildIndexes" : true,
                        "hidden" : false,
                        "priority" : 10,
                        "tags" : {

                        },
                        "slaveDelay" : NumberLong(0),
                        "votes" : 1
                },
                {
                        "_id" : 3,
                        "host" : "node01:27017",
                        "arbiterOnly" : true,
                        "buildIndexes" : true,
                        "hidden" : false,
                        "priority" : 0,
                        "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("5faa85853d5a2d8fdf8af85e")
        }
}
test_replset:PRIMARY>

　　提示：能夠看到node01節點上的arbiterOnly屬性已經啓用，說明這就是一個仲裁節點；咱們說過仲裁節點上沒有保存副本，咱們到node01上看看是否保存的有副本集數據呢？

test_replset:ARBITER> show databases
uncaught exception: Error: listDatabases failed:{
        "topologyVersion" : {
                "processId" : ObjectId("5faa9d87e504fa222c4a584d"),
                "counter" : NumberLong(1)
        },
        "ok" : 0,
        "errmsg" : "not master and slaveOk=false",
        "code" : 13435,
        "codeName" : "NotMasterNoSlaveOk"
} :
_getErrorWithCode@src/mongo/shell/utils.js:25:13
Mongo.prototype.getDBs/<@src/mongo/shell/mongo.js:147:19
Mongo.prototype.getDBs@src/mongo/shell/mongo.js:99:12
shellHelper.show@src/mongo/shell/utils.js:937:13
shellHelper@src/mongo/shell/utils.js:819:15
@(shellhelp2):1:1
test_replset:ARBITER> rs.secondaryOk()
test_replset:ARBITER> show databases
uncaught exception: Error: listDatabases failed:{
        "topologyVersion" : {
                "processId" : ObjectId("5faa9d87e504fa222c4a584d"),
                "counter" : NumberLong(1)
        },
        "ok" : 0,
        "errmsg" : "node is not in primary or recovering state",
        "code" : 13436,
        "codeName" : "NotMasterOrSecondary"
} :
_getErrorWithCode@src/mongo/shell/utils.js:25:13
Mongo.prototype.getDBs/<@src/mongo/shell/mongo.js:147:19
Mongo.prototype.getDBs@src/mongo/shell/mongo.js:99:12
shellHelper.show@src/mongo/shell/utils.js:937:13
shellHelper@src/mongo/shell/utils.js:819:15
@(shellhelp2):1:1
test_replset:ARBITER>

　　提示：咱們在仲裁節點上查看數據庫列表，它提示咱們不是主節點和從節點，不容許讀；既然都不容許讀，寫確定是沒有辦法進行；

　　ok,到此mongodb的副本集的配置、測試就到此爲止；