MongoDB之Replica Set(复制集复制)

MongoDB支持两种复制模式：

• 主从复制(Master/Slave)
• 复制集复制(Replica Set)

下面主要记录我在centos虚拟机上安装replica set，主要参考：http://docs.mongodb.org/manual/tutorial/deploy-replica-set/

首先准备好3份配置文件：

 port = 27017

 dbpath = /home/bells/install/data1
 logpath = /home/bells/install/log1/1.log

 fork = true
 replSet = rs0

 port = 27016

 dbpath = /home/bells/install/data2
 logpath = /home/bells/install/log2/2.log

 fork = true
 replSet = rs0

 port = 27015

 dbpath = /home/bells/install/data3
 logpath = /home/bells/install/log3/3.log

 fork = true
 replSet = rs0

然后再启动这3个mongodb服务

sudo ./mongodb1/bin/mongod --smallfiles --config 1.conf
sudo ./mongodb2/bin/mongod --smallfiles --config 2.conf
sudo ./mongodb3/bin/mongod --smallfiles --config 3.conf

其实smallfiles也应该写进*.conf文件中的。

最后配置：

主要是通过下面的命令

rs.initiate()   使用默认的配置初始化replica set在当前的服务器

rs.status()    显示当前replica set的状态

rs.add(serverInfo)   增加新的成员到replica set 中

rs.addArb(serverInfo)    增加一个arbiter到replica set中

 rs.initiate()
 {
     "info2" : "no configuration explicitly specified -- making one",
     "me" : "localhost.localdomain:27017",
     "info" : "Config now saved locally.  Should come online in about a minute.",
     "ok" : 1
 }
 > rs.conf()
 {
     "_id" : "rs0",
     "version" : 1,
     "members" : [
         {
             "_id" : 0,
             "host" : "localhost.localdomain:27017"
         }
     ]
 }
 rs0:PRIMARY> rs.add("localhost.localdomain:27016")
 { "ok" : 1 }
 rs0:PRIMARY> rs.add("localhost.localdomain:27015")
 { "ok" : 1 }
 rs0:PRIMARY> rs.status()
 {
     "set" : "rs0",
     "date" : ISODate("2014-02-23T01:43:16Z"),
     "myState" : 1,
     "members" : [
         {
             "_id" : 0,
             "name" : "localhost.localdomain:27017",
             "health" : 1,
             "state" : 1,
             "stateStr" : "PRIMARY",
             "uptime" : 602,
             "optime" : Timestamp(1393119782, 1),
             "optimeDate" : ISODate("2014-02-23T01:43:02Z"),
             "self" : true
         },
         {
             "_id" : 1,
             "name" : "localhost.localdomain:27016",
             "health" : 1,
             "state" : 5,
             "stateStr" : "STARTUP2",
             "uptime" : 17,
             "optime" : Timestamp(0, 0),
             "optimeDate" : ISODate("1970-01-01T00:00:00Z"),
             "lastHeartbeat" : ISODate("2014-02-23T01:43:15Z"),
             "lastHeartbeatRecv" : ISODate("2014-02-23T01:43:15Z"),
             "pingMs" : 0,
             "lastHeartbeatMessage" : "initial sync need a member to be primary or secondary to do our initial sync"
         },
         {
             "_id" : 2,
             "name" : "localhost.localdomain:27015",
             "health" : 1,
             "state" : 5,
             "stateStr" : "STARTUP2",
             "uptime" : 14,
             "optime" : Timestamp(0, 0),
             "optimeDate" : ISODate("1970-01-01T00:00:00Z"),
             "lastHeartbeat" : ISODate("2014-02-23T01:43:16Z"),
             "lastHeartbeatRecv" : ISODate("2014-02-23T01:43:16Z"),
             "pingMs" : 1,
             "lastHeartbeatMessage" : "syncThread: 12520 new file allocation failure"
         }
     ],
     "ok" : 1
 }
 rs0:PRIMARY> db.person.insert({"name":"jack", "age":20})
 rs0:PRIMARY> db.person.find()
 { "_id" : ObjectId("5309529869d3a7216c59ef2a"), "name" : "jack", "age" : 20 }

 [bells@localhost install]$ ./mongodb2/bin/mongo --port 27016
 MongoDB shell version: 2.4.5
 connecting to: 127.0.0.1:27016/test
 rs0:SECONDARY> db.person.find()
 error: { "$err" : "not master and slaveOk=false", "code" : 13435 }
 rs0:SECONDARY> rs.slaveOk();
 rs0:SECONDARY> db.person.find()
 { "_id" : ObjectId("5309529869d3a7216c59ef2a"), "name" : "jack", "age" : 20 }

安装部署过程中，遇到两个问题：

1. 启动mongodb时，错误日志：

 Sun Feb 23 09:47:57.930 [initandlisten] ERROR: Insufficient free space for journal files
 Sun Feb 23 09:47:57.930 [initandlisten] Please make at least 3379MB available in /home/bells/install/data1/journal or use --smallfiles
 Sun Feb 23 09:47:57.930 [initandlisten]
 Sun Feb 23 09:47:57.953 [initandlisten] exception in initAndListen: 15926 Insufficient free space for journals, terminating

解决办法就是，启动的时候，加个   --smallfiles ： 这个参数默认值是false，如果设为true，则会是每个文件最大的大小限定为512M而不是默认的2G

2. 在secondary中，查询时：

 rs0:SECONDARY> db.person.find()
 error: { "$err" : "not master and slaveOk=false", "code" : 13435 }

这个是正常的，因为SECONDARY默认是不允许读写操作的，可以：

rs0:SECONDARY> db.slaveOk();

来解决！