MongoDB主从复制
介绍了Mongodb的安装使用，在 MongoDB 中,有两种数据冗余方式,一种 是 Master-Slave 模式（主从复制）,一种是 Replica Sets 模式（副本集）。
Mongodb一共有三种集群搭建的方式： Replica Set（副本集）、 Sharding（切片） Master-Slaver（主从）【目前已不推荐使用了！！！】 其中，Sharding集群也是三种集群中最复杂的。 副本集比起主从可以实现故障转移！！非常使用！ mongoDB目前已不推荐使用主从模式，取而代之的是副本集模式。副本集其实一种互为主从的关系，可理解为主主。 副本集指将数据复制，多份保存，不同服务器保存同一份数据，在出现故障时自动切换。对应的是数据冗余、备份、镜像、读写分离、高可用性等关键词； 而分片则指为处理大量数据，将数据分开存储，不同服务器保存不同的数据，它们的数据总和即为整个数据集。追求的是高性能。 在生产环境中，通常是这两种技术结合使用，分片+副本集。
mongodb主从复制配置
有些版本已经不支持主从复制（本人环境为mongodb4.0版本，已经不支持主从复制）
主从复制是MongoDB最常用的复制方式,也是一个简单的数据库同步备份的集群技术,这种方式很灵活.可用于备份,故障恢复,读扩展等.
最基本的设置方式就是建立一个主节点和一个或多个从节点,每个从节点要知道主节点的地址。采用双机备份后主节点挂掉了后从节点可以接替主机继续服务。所以这种模式比单节点的高可用性要好很多。
配置主从复制的注意点
1）在数据库集群中要明确的知道谁是主服务器,主服务器只有一台. 2）从服务器要知道自己的数据源也就是对应的主服务是谁. 3）--master用来确定主服务器,--slave 和 --source 来控制从服务器
可以在mongodb.conf配置文件里指明主从关系，这样启动mongodb的时候只要跟上配置文件就行，就不需要通过--master和--slave来指明主从了。
下面简单记录下Mongodb主从复制的部署过程
1）机器环境 182.48.115.238 master-node 182.48.115.236 slave-node 两台机器都关闭防火墙和selinux mongodb的安装参考：http://www.cnblogs.com/kevingrace/p/5752382.html 2）主从配置 .............master－node节点配置............. [root@master-node ~]# vim /usr/local/mongodb/mongodb.conf port=27017 bind_ip = 182.48.115.238 dbpath=/usr/local/mongodb/data logpath=/usr/local/mongodb/log/mongo.log logappend=true journal = true fork = true master = true //确定自己是主服务器 [root@master-node ~]# nohup /usr/local/mongodb/bin/mongod --config /usr/local/mongodb/mongodb.conf & [root@master-node ~]# ps -ef|grep mongodb root 15707 15514 23 16:45 pts/2 00:00:00 /usr/local/mongodb/bin/mongod --config /usr/local/mongodb/mongodb.conf root 15736 15514 0 16:45 pts/2 00:00:00 grep mongodb [root@master-node ~]# lsof -i:27017 COMMAND PID USER FD TYPE DEVICE SIZE/OFF NODE NAME mongod 15707 root 7u IPv4 153114 0t0 TCP 182.48.115.238:27017 (LISTEN) 由于mongodb.conf里绑定了本机的ip地址182.48.115.238，所以连接mongodb的时候必须用这个ip地址，不能使用默认的127.0.0.1，也就是说： [root@master-node ~]# mongo 182.48.115.238:27017 //这样才能连接mongodb [root@master-node ~]# mongo 或者 mongodb 127.0.0.1:27017 // 这样不能连接mongodb .............slave－node节点配置............. [root@slave-node ~]# vim /usr/local/mongodb/mongodb.conf port=27017 dbpath=/usr/local/mongodb/data logpath=/usr/local/mongodb/log/mongo.log logappend=true journal = true fork = true bind_ip = 182.48.115.236 //确定主数据库端口 source = 182.48.115.238:27017 //确定主数据库端口 slave = true //确定自己是从服务器 [root@slave-node ~]# nohup /usr/local/mongodb/bin/mongod --config /usr/local/mongodb/mongodb.conf & [root@slave-node ~]# ps -ef|grep mongo root 26290 26126 8 16:47 pts/0 00:00:00 /usr/local/mongodb/bin/mongod --config /usr/local/mongodb/mongodb.conf root 26316 26126 0 16:47 pts/0 00:00:00 grep mongo [root@slave-node ~]# lsof -i:27017 COMMAND PID USER FD TYPE DEVICE SIZE/OFF NODE NAME mongod 26290 root 7u IPv4 663904 0t0 TCP slave-node1:27017 (LISTEN) mongod 26290 root 25u IPv4 663917 0t0 TCP slave-node1:51060->slave-node2:27017 (ESTABLISHED) 在slave-node测试连接master-node的mongodb数据库是否正常 [root@slave-node ~]# mongo 182.48.115.236:27017 MongoDB shell version v3.4.4 connecting to: 182.48.115.236:27017 MongoDB server version: 3.4.4 Server has startup warnings: 2017-06-03T16:47:31.200+0800 I STORAGE [initandlisten] 2017-06-03T16:47:31.200+0800 I STORAGE [initandlisten] ** WARNING: Using the XFS filesystem is strongly recommended with the WiredTiger storage engine 2017-06-03T16:47:31.200+0800 I STORAGE [initandlisten] ** See http://dochub.mongodb.org/core/prodnotes-filesystem 2017-06-03T16:47:32.472+0800 I CONTROL [initandlisten] 2017-06-03T16:47:32.472+0800 I CONTROL [initandlisten] ** WARNING: Access control is not enabled for the database. 2017-06-03T16:47:32.472+0800 I CONTROL [initandlisten] ** Read and write access to data and configuration is unrestricted. 2017-06-03T16:47:32.472+0800 I CONTROL [initandlisten] ** WARNING: You are running this process as the root user, which is not recommended. 2017-06-03T16:47:32.472+0800 I CONTROL [initandlisten] 2017-06-03T16:47:32.473+0800 I CONTROL [initandlisten] 2017-06-03T16:47:32.473+0800 I CONTROL [initandlisten] ** WARNING: /sys/kernel/mm/transparent_hugepage/enabled is 'always'. 2017-06-03T16:47:32.473+0800 I CONTROL [initandlisten] ** We suggest setting it to 'never' 2017-06-03T16:47:32.473+0800 I CONTROL [initandlisten] 2017-06-03T16:47:32.473+0800 I CONTROL [initandlisten] ** WARNING: /sys/kernel/mm/transparent_hugepage/defrag is 'always'. 2017-06-03T16:47:32.473+0800 I CONTROL [initandlisten] ** We suggest setting it to 'never' 2017-06-03T16:47:32.473+0800 I CONTROL [initandlisten] > 3）主从数据同步测试 在master-node节点数据库里创建master_slave库，并插入20条数据 [root@master-node ~]# mongo 182.48.115.238:27017 MongoDB shell version v3.4.4 connecting to: 182.48.115.238:27017 MongoDB server version: 3.4.4 Server has startup warnings: 2017-06-03T16:45:07.406+0800 I STORAGE [initandlisten] 2017-06-03T16:45:07.407+0800 I STORAGE [initandlisten] ** WARNING: Using the XFS filesystem is strongly recommended with the WiredTiger storage engine 2017-06-03T16:45:07.407+0800 I STORAGE [initandlisten] ** See http://dochub.mongodb.org/core/prodnotes-filesystem 2017-06-03T16:45:08.373+0800 I CONTROL [initandlisten] 2017-06-03T16:45:08.373+0800 I CONTROL [initandlisten] ** WARNING: Access control is not enabled for the database. 2017-06-03T16:45:08.373+0800 I CONTROL [initandlisten] ** Read and write access to data and configuration is unrestricted. 2017-06-03T16:45:08.373+0800 I CONTROL [initandlisten] ** WARNING: You are running this process as the root user, which is not recommended. 2017-06-03T16:45:08.373+0800 I CONTROL [initandlisten] 2017-06-03T16:45:08.374+0800 I CONTROL [initandlisten] 2017-06-03T16:45:08.374+0800 I CONTROL [initandlisten] ** WARNING: /sys/kernel/mm/transparent_hugepage/enabled is 'always'. 2017-06-03T16:45:08.374+0800 I CONTROL [initandlisten] ** We suggest setting it to 'never' 2017-06-03T16:45:08.374+0800 I CONTROL [initandlisten] 2017-06-03T16:45:08.374+0800 I CONTROL [initandlisten] ** WARNING: /sys/kernel/mm/transparent_hugepage/defrag is 'always'. 2017-06-03T16:45:08.374+0800 I CONTROL [initandlisten] ** We suggest setting it to 'never' 2017-06-03T16:45:08.374+0800 I CONTROL [initandlisten] > use master_slave switched to db master_slave > function add(){var i = 0;for(;i<20;i++){db.persons.insert({"name":"wang"+i})}} > add() > db.persons.find() { "_id" : ObjectId("593278699a9e2e9f37ac4dbb"), "name" : "wang0" } { "_id" : ObjectId("593278699a9e2e9f37ac4dbc"), "name" : "wang1" } { "_id" : ObjectId("593278699a9e2e9f37ac4dbd"), "name" : "wang2" } { "_id" : ObjectId("593278699a9e2e9f37ac4dbe"), "name" : "wang3" } { "_id" : ObjectId("593278699a9e2e9f37ac4dbf"), "name" : "wang4" } { "_id" : ObjectId("593278699a9e2e9f37ac4dc0"), "name" : "wang5" } { "_id" : ObjectId("593278699a9e2e9f37ac4dc1"), "name" : "wang6" } { "_id" : ObjectId("593278699a9e2e9f37ac4dc2"), "name" : "wang7" } { "_id" : ObjectId("593278699a9e2e9f37ac4dc3"), "name" : "wang8" } { "_id" : ObjectId("593278699a9e2e9f37ac4dc4"), "name" : "wang9" } { "_id" : ObjectId("593278699a9e2e9f37ac4dc5"), "name" : "wang10" } { "_id" : ObjectId("593278699a9e2e9f37ac4dc6"), "name" : "wang11" } { "_id" : ObjectId("593278699a9e2e9f37ac4dc7"), "name" : "wang12" } { "_id" : ObjectId("593278699a9e2e9f37ac4dc8"), "name" : "wang13" } { "_id" : ObjectId("593278699a9e2e9f37ac4dc9"), "name" : "wang14" } { "_id" : ObjectId("593278699a9e2e9f37ac4dca"), "name" : "wang15" } { "_id" : ObjectId("593278699a9e2e9f37ac4dcb"), "name" : "wang16" } { "_id" : ObjectId("593278699a9e2e9f37ac4dcc"), "name" : "wang17" } { "_id" : ObjectId("593278699a9e2e9f37ac4dcd"), "name" : "wang18" } { "_id" : ObjectId("593278699a9e2e9f37ac4dce"), "name" : "wang19" } Type "it" for more 然后在slave-node节点数据库里查看，是否将master-node写入的新数据同步过来了 [root@slave-node log]# mongo 182.48.115.236:27017 MongoDB shell version v3.4.4 connecting to: 182.48.115.236:27017 MongoDB server version: 3.4.4 Server has startup warnings: 2017-06-03T16:56:28.928+0800 I STORAGE [initandlisten] 2017-06-03T16:56:28.928+0800 I STORAGE [initandlisten] ** WARNING: Using the XFS filesystem is strongly recommended with the WiredTiger storage engine 2017-06-03T16:56:28.928+0800 I STORAGE [initandlisten] ** See http://dochub.mongodb.org/core/prodnotes-filesystem 2017-06-03T16:56:29.883+0800 I CONTROL [initandlisten] 2017-06-03T16:56:29.883+0800 I CONTROL [initandlisten] ** WARNING: Access control is not enabled for the database. 2017-06-03T16:56:29.883+0800 I CONTROL [initandlisten] ** Read and write access to data and configuration is unrestricted. 2017-06-03T16:56:29.883+0800 I CONTROL [initandlisten] ** WARNING: You are running this process as the root user, which is not recommended. 2017-06-03T16:56:29.883+0800 I CONTROL [initandlisten] 2017-06-03T16:56:29.884+0800 I CONTROL [initandlisten] 2017-06-03T16:56:29.884+0800 I CONTROL [initandlisten] ** WARNING: /sys/kernel/mm/transparent_hugepage/enabled is 'always'. 2017-06-03T16:56:29.884+0800 I CONTROL [initandlisten] ** We suggest setting it to 'never' 2017-06-03T16:56:29.884+0800 I CONTROL [initandlisten] 2017-06-03T16:56:29.884+0800 I CONTROL [initandlisten] ** WARNING: /sys/kernel/mm/transparent_hugepage/defrag is 'always'. 2017-06-03T16:56:29.884+0800 I CONTROL [initandlisten] ** We suggest setting it to 'never' 2017-06-03T16:56:29.884+0800 I CONTROL [initandlisten] > show dbs 2017-06-03T17:10:32.136+0800 E QUERY [thread1] Error: listDatabases failed:{ "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:62:1 shellHelper.show@src/mongo/shell/utils.js:769:19 shellHelper@src/mongo/shell/utils.js:659:15 @(shellhelp2):1:1 > rs.slaveOk(); > show dbs admin 0.000GB local 0.000GB master_slave 0.000GB wangshibo 0.000GB > use master_slave switched to db master_slave > db.persons.find() { "_id" : ObjectId("593278699a9e2e9f37ac4dbb"), "name" : "wang0" } { "_id" : ObjectId("593278699a9e2e9f37ac4dbc"), "name" : "wang1" } { "_id" : ObjectId("593278699a9e2e9f37ac4dbd"), "name" : "wang2" } { "_id" : ObjectId("593278699a9e2e9f37ac4dbe"), "name" : "wang3" } { "_id" : ObjectId("593278699a9e2e9f37ac4dbf"), "name" : "wang4" } { "_id" : ObjectId("593278699a9e2e9f37ac4dc0"), "name" : "wang5" } { "_id" : ObjectId("593278699a9e2e9f37ac4dc1"), "name" : "wang6" } { "_id" : ObjectId("593278699a9e2e9f37ac4dc2"), "name" : "wang7" } { "_id" : ObjectId("593278699a9e2e9f37ac4dc3"), "name" : "wang8" } { "_id" : ObjectId("593278699a9e2e9f37ac4dc4"), "name" : "wang9" } { "_id" : ObjectId("593278699a9e2e9f37ac4dc5"), "name" : "wang10" } { "_id" : ObjectId("593278699a9e2e9f37ac4dc6"), "name" : "wang11" } { "_id" : ObjectId("593278699a9e2e9f37ac4dc7"), "name" : "wang12" } { "_id" : ObjectId("593278699a9e2e9f37ac4dc8"), "name" : "wang13" } { "_id" : ObjectId("593278699a9e2e9f37ac4dc9"), "name" : "wang14" } { "_id" : ObjectId("593278699a9e2e9f37ac4dca"), "name" : "wang15" } { "_id" : ObjectId("593278699a9e2e9f37ac4dcb"), "name" : "wang16" } { "_id" : ObjectId("593278699a9e2e9f37ac4dcc"), "name" : "wang17" } { "_id" : ObjectId("593278699a9e2e9f37ac4dcd"), "name" : "wang18" } { "_id" : ObjectId("593278699a9e2e9f37ac4dce"), "name" : "wang19" } Type "it" for more ........................................................................................ 如果在slave-node节点上的数据库中查看，有报错："errmsg" : "not master and slaveOk=false"！！！ 首先这是正常的，因为SECONDARY是不允许读写的， 在写多读少的应用中，使用Replica Sets来实现读写分离。 通过在连接时指定或者在主库指定slaveOk，由Secondary来分担读的压力，Primary只承担写操作。 对于replica set 中的secondary 节点默认是不可读的。 解决办法： 在slave-node节点数据库中执行"rs.slaveOk();"命令即可 ........................................................................................ 在slave-node节点数据库中发现已经同步过来了master_slave库的20条数据，说明mongodb的主从复制环境已经成功了！当配置完主从服务器后，一但主服务器上的数据发生变化，从服务器也会发生变化
主从复制的原理
在主从结构中，主节点的操作记录成为oplog（operation log）。oplog存储在一个系统数据库local的集合oplog.$main中，这个集合的每个文档都代表主节点上执行的一个操作。 从服务器会定期从主服务器中获取oplog记录，然后在本机上执行！对于存储oplog的集合，MongoDB采用的是固定集合，也就是说随着操作过多，新的操作会覆盖旧的操作！ 主从复制的其他设置项 --only 从节点指定复制某个数据库,默认是复制全部数据库 --slavedelay 从节点设置主数据库同步数据的延迟(单位是秒) --fastsync 从节点以主数据库的节点快照为节点启动从数据库 --autoresync 从节点如果不同步则从新同步数据库(即选择当通过热添加了一台从服务器之后，从服务器选择是否更新主服务器之间的数据) --oplogSize 主节点设置oplog的大小(主节点操作记录存储到local的oplog中)
在上面slave-node从节点的local数据库中，存在一个集合sources。这个集合就保存了这个服务器的主服务器是谁
[root@slave-node mongodb]# mongo 182.48.115.236:27017 ...... > show dbs admin 0.000GB local 0.000GB master_slave 0.000GB wangshibo 0.000GB > use local switched to db local > show collections me sources startup_log > db.sources.find() { "_id" : ObjectId("593277a5105051e5648605a3"), "host" : "182.48.115.238:27017", "source" : "main", "syncedTo" : Timestamp(1496481652, 1) } >
