mongodb replication

1：master-slave replication

主从复制：一个服务启动的时候加上--master参数，另一个服务启动时加上--slave和--source参数就可以实现同步了。

一个master服务可以有一个或者多个slave，每一个salve都知道master的地址，如图：

举例：

启动master

$ mkdir -p ~/dbs/master
$ ./mongod --dbpath ~/dbs/master --port 10000 --master

建立相关目录，启动的时候加上--master即可

启动slave

$ mkdir -p ~/dbs/slave
$ ./mongod --dbpath ~/dbs/slave --port 10001 --slave --source localhost:10000

建立目录，启动这里的localhost就是上面master的地址，不管是一个slave还是多个，都是从master进行复制

Adding and Removing Sources：

$ ./mongod --slave --dbpath ~/dbs/slave --port 27018 --没有指定source

启动之后如果要加入一个slave，localhost:27017为master

> use local
> db.sources.insert({"host" : "localhost:27017"})

2：replica sets 复制集

这个是1.6开发的新功能，与之前的主从复制比起来，功能更加强大，多了故障转移和自动修复节点，每个DB的数据完全一致。

建立相关目录：

数据目录：mkdir -p /mongodb1.8/data1/

mkdir -p /mongodb1.8/data2/

mkdir -p /mongodb1.8/data3/

日志文件：touch /mongodb1.8/RS.log /mongodb1.8/RS1.log /mongodb1.8/RS2.log

创建主从KEY文件：mkdir -p /mongodb1.8/key

echo "this is rs1 super secret key" > /mongodb1.8/key/r1

echo "this is rs1 super secret key" > /mongodb1.8/key/r2

echo "this is rs1 super secret key" > /mongodb1.8/key/r3

这里KEY的权限400

chmod 400 /mongodb1.8/key/r1 /mongodb1.8/key/r2 /mongodb1.8/key/r3

启动一个server，记得/etc/hosts文件里面包含localhost记录，否则无法解析

mongod --replSet rs1/localhost:20001 --keyFile /mongodb1.8/key/r1 --fork --port 20001 --dbpath /mongodb1.8/data1/ --logpath=/mongodb1.8/RS.log

mongod --replSet rs1/localhost:20002 --keyFile /mongodb1.8/key/r2 --fork --port 20002 --dbpath /mongodb1.8/data2/ --logpath=/mongodb1.8/RS1.log

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mongod --replSet rs1/localhost:20003 --keyFile /mongodb1.8/key/r3 --fork --port 20003 --dbpath /mongodb1.8/data3/ --logpath=/mongodb1.8/RS2.log

mongo localhost:20001/admin

config_rs1 = {_id: 'rs1', members: [
... {_id: 0, host: 'localhost:20001', priority:1}, --成员IP 及端口，priority=1 指PRIMARY
... {_id: 1, host: 'localhost:20002'},
... {_id: 2, host: 'localhost:20003'}]
... }

初始化配置：
rs.initiate(config_rs1);

或者db.runCommand({"replSetInitiate" : {
... "_id" : "rs1",
... "members" : [
... {
... "_id" : 0,
... "host" : "localhost:20001"
... },
... {
... "_id" : 1,
... "host" : "localhost:20002"
... },
... {
... "_id" : 2,
... "host" : "localhost:20003"
... }
... ]}})

rs1:PRIMARY> 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([secs]) step down as primary (momentarily) (disconnects)
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.slaveOk() shorthand for db.getMongo().setSlaveOk()

db.isMaster() check who is primary

或者使用命令:
db.runCommand({})
* { isMaster : 1 }
* { replSetGetStatus : 1 }
* { replSetInitiate : <config> }
* { replSetReconfig: <config> }
* { replSetStepDown : <seconds> }
* { replSetFreeze : <seconds> }
查看状态：

rs.status()

rs.isMaster()

主从日志oplpg

rs就是通过oplog的记录写操作，他是一个固定长度的copped collection，存放于local数据库下，oplog的参数是可以通过--oplogSize来调整的，可以查看db.oplog.rs.find()，看到操作记录。

db.printReplicationInfo()查看元数据信息

db.printSlaveReplicationInfo()查看slave的同步状态

在local库下db.system.replset.find()，可以查询到主从库的信息=rs.conf()

默认从库是不可读的，如果需要来分担主库压力，可以打开读，举例：

[mongo@172_16_3_216 ~]$ mongo 127.0.0.1:20002
MongoDB shell version: 1.8.4
connecting to: 127.0.0.1:20002/test
myrs:SECONDARY> show collections
Mon Nov 14 15:20:30 uncaught exception: error: { "$err" : "not master and slaveok=false", "code" : 13435 }
myrs:SECONDARY> db.get
db.getCollection( db.getLastErrorCmd( db.getName( db.getProfilingStatus( db.getSisterDB(
db.getCollectionNames( db.getLastErrorObj( db.getPrevError( db.getReplicationInfo(
db.getLastError( db.getMongo( db.getProfilingLevel( db.getSiblingDB(
myrs:SECONDARY> db.getMongo().setSlaveOk()
not master and slaveok=false
myrs:SECONDARY> show collections
hank
system.indexes
myrs:SECONDARY> db.hank.find()
{ "_id" : ObjectId("4ec0bdf9a9888d970cdc6197"), "name" : "zhang" }
{ "_id" : ObjectId("4ec0bdfba9888d970cdc6198"), "name" : "zhang" }
{ "_id" : ObjectId("4ec0bdfba9888d970cdc6199"), "name" : "zhang" }
{ "_id" : ObjectId("4ec0bdfca9888d970cdc619a"), "name" : "zhang" }
{ "_id" : ObjectId("4ec0bdfca9888d970cdc619b"), "name" : "zhang" }
{ "_id" : ObjectId("4ec0bdfca9888d970cdc619c"), "name" : "zhang" }
{ "_id" : ObjectId("4ec0be05a9888d970cdc619d"), "name" : "zhang", "age" : 80 }
{ "_id" : ObjectId("4ec0be06a9888d970cdc619e"), "name" : "zhang", "age" : 80 }
{ "_id" : ObjectId("4ec0be06a9888d970cdc619f"), "name" : "zhang", "age" : 80 }
{ "_id" : ObjectId("4ec0be07a9888d970cdc61a0"), "name" : "zhang", "age" : 80 }
{ "_id" : ObjectId("4ec0be07a9888d970cdc61a1"), "name" : "zhang", "age" : 80 }

这样就可以读了