MongoDB的auto-sharding功能是指mongodb通过mongos自动建立一个水平扩展的数据库集群系统，将数据库分表存储在sharding的各个节点上。
一个mongodb集群包括一些shards（包括一些mongod进程），mongos路由进程，一个或多个config服务器
Shards
每一个shard包括一个或多个服务和存储数据的mongod进程（mongod是MongoDB数据的核心进程）
典型的每个shard开启多个服务来提高服务的可用性。这些服务/mongod进程在shard中组成一个复制集
Chunks
Chunk是一个来自特殊集合中的一个数据范围，（collection，minKey，maxKey）描叙一个chunk，它介于minKey和maxKey范围之间。
例如chunks 的maxsize大小是100M，如果一个文件达到或超过这个范围时，会被切分到2个新的chunks中。当一个shard的数据过量时，chunks将会被迁移到其他的shards上。同样，chunks也可以迁移到其他的shards上
Config Servers
Config服务器存储着集群的metadata信息，包括每个服务器，每个shard的基本信息和chunk信息
Config服务器主要存储的是chunk信息。每一个config服务器都复制了完整的chunk信息。
配置：（模拟2个shard服务和一个config服务）
Shard1：27020
Shard2：27021
Config：27022
Mongos启动时默认使用的27017端口
新建存放数据的目录
[falcon@www.fwphp.cn ~/mongodata]mkdir270202702127022[falcon@www.fwphp.cn /mongodata]mkdir270202702127022[falcon@www.fwphp.cn /mongodata] ls
27020 27021 27022
[falcon@www.fwphp.cn ~/mongodb/bin]./mongod --dbpath /home/falcon/mongodata/27020 --port 27020 > /home/falcon/mongodata/27020.log &
[falcon@www.fwphp.cn ~/mongodb/bin]./mongod --dbpath /home/falcon/mongodata/27020 --port 27020 > /home/falcon/mongodata/27020.log & [falcon@www.fwphp.cn ~/mongodb/bin]./mongod --dbpath /home/falcon/mongodata/27021 --port 27021 > /home/falcon/mongodata/27021.log &
[falcon@www.fwphp.cn ~/mongodb/bin]$ ./mongod --dbpath /home/falcon/mongodata/27022 --port 27022 > /home/falcon/mongodata/27022.log &
启动mongos时，默认开启了27017端口
[falcon@www.fwphp.cn ~/mongodb/bin]$ ./mongos --configdb localhost:27022 > /home/falcon/mongodata/config.log &
检查是否启动
[falcon@www.fwphp.cn ~/mongodb/bin]ps−ef|grepmongofalcon26121020:15?00:00:00./mongod−−dbpath/home/falcon/mongodata/27020−−port27020falcon26191020:15?00:00:00./mongod−−dbpath/home/falcon/mongodata/27021−−port27021falcon26251020:15?00:00:00./mongod−−dbpath/home/falcon/mongodata/27022−−port27022falcon26581020:15?00:00:00./mongos−−configdblocalhost:27022falcon28042772020:31pts/000:00:00bin/mongofalcon28472812020:55pts/200:00:00grepmongo[falcon@www.fwphp.cn /mongodb/bin]ps−ef|grepmongofalcon26121020:15?00:00:00./mongod−−dbpath/home/falcon/mongodata/27020−−port27020falcon26191020:15?00:00:00./mongod−−dbpath/home/falcon/mongodata/27021−−port27021falcon26251020:15?00:00:00./mongod−−dbpath/home/falcon/mongodata/27022−−port27022falcon26581020:15?00:00:00./mongos−−configdblocalhost:27022falcon28042772020:31pts/000:00:00bin/mongofalcon28472812020:55pts/200:00:00grepmongo[falcon@www.fwphp.cn /mongodb/bin]
[falcon@www.fwphp.cn ~/mongodb/bin]$ netstat -an -t
Active Internet connections (servers and established)
Proto Recv-Q Send-Q Local Address Foreign Address State
tcp 0 0 0.0.0.0:10022 0.0.0.0:* LISTEN
tcp 0 0 0.0.0.0:27017 0.0.0.0:* LISTEN
tcp 0 0 0.0.0.0:587 0.0.0.0:* LISTEN
tcp 0 0 0.0.0.0:27020 0.0.0.0:* LISTEN
tcp 0 0 0.0.0.0:27021 0.0.0.0:* LISTEN
tcp 0 0 0.0.0.0:27022 0.0.0.0:* LISTEN
......
tcp 0 0 0.0.0.0:28020 0.0.0.0:* LISTEN
tcp 0 0 0.0.0.0:28021 0.0.0.0:* LISTEN
tcp 0 0 0.0.0.0:28022 0.0.0.0:* LISTEN
tcp 0 0 127.0.0.1:631 0.0.0.0:* LISTEN
........
看到以上信息证明mongodb启动完整，对于开启的28020、28021、28022是对于的http接口
[falcon@www.fwphp.cn ~/mongodb/bin]$ ./mongo 默认连接到mongos上
MongoDB shell version: 1.2.4-
url: test
connecting to: test
type "help" for help
> show dbs
admin
config
Local
加入shard节点
> use admin
switched to db admin
> db.runCommand( { addshard : "localhost:27020", allowLocal : true } )
{"ok" : 1 , "added" : "localhost:27020"}
> db.runCommand( { addshard : "localhost:27021", allowLocal : true } )
{"ok" : 1 , "added" : "localhost:27021"}
> db.runCommand({listshards:1}); 查看shard节点列表
{
"shards" : [
{
"_id" : ObjectId("4b9cd380c33000afad27718e"),
"host" : "localhost:27020"
},
{
"_id" : ObjectId("4b9cd381c33000afad27718f"),
"host" : "localhost:27021"
}
],
"ok" : 1
}
新建自动切片的库user001：
> config = connect("localhost:27022")
> config = config.getSisterDB("config")
> user001=db.getSisterDB("user001");
user001
> db.runCommand({enablesharding:"user001"})
{ "ok" : 1 }
> db.printShardingStatus();
--- Sharding Status ---
sharding version: { "_id" : ObjectId("4b9cd354c33000afad27718d"), "version" : 2 }
shards:
{ "_id" : ObjectId("4b9cd380c33000afad27718e"), "host" : "localhost:27020" }
{ "_id" : ObjectId("4b9cd381c33000afad27718f"), "host" : "localhost:27021" }
databases:
{ "name" : "admin", "partitioned" : false, "primary" : "localhost:27022", "_id" : ObjectId("4b9cd3776693dcfa468dec13") }
{ "name" : "user001", "partitioned" : true, "primary" : "localhost:27021", "_id" : ObjectId("4b9cde866693dcfa468dec17") }
my chunks
我们来在user001中新建表，插入数据
> use user001
switched to db user001
> db.createCollection("user_001")
{ "ok" : 1 }
> show collections
system.indexes
user_001
> db.user_001.insert({uid:1,username:"Falcon.C",sex:"男",age:25});
> db.user_001.find();
{ "_id" : ObjectId("4b9ce1a6c84d7f20576c4df1"), "uid" : 1, "username" : "Falcon.C", "sex" : "男", "age" : 25 }
我们来看看user001库被分配到了哪个shard上
[falcon@www.fwphp.cn ~/mongodata]ls−R.:270202702127022mongos.log./27020:27020.logmongod.locktest.0test.1test.nstmp./27020/tmp:./27021:27021.logmongod.locktmpuser.0user001.0user001.1user001.nsuser.1user.ns./27021/tmp:./27022:27022.logconfig.0config.nsmongod.lockmongos.logtmp./27022/tmp:[falcon@www.fwphp.cn /mongodata]ls−R.:270202702127022mongos.log./27020:27020.logmongod.locktest.0test.1test.nstmp./27020/tmp:./27021:27021.logmongod.locktmpuser.0user001.0user001.1user001.nsuser.1user.ns./27021/tmp:./27022:27022.logconfig.0config.nsmongod.lockmongos.logtmp./27022/tmp:[falcon@www.fwphp.cn /mongodata]
从以上的文件可以看出，user001被分配到了27021的shard上了，但是通过mongos路由，我们并感觉不到是数据存放在哪个shard的chunk上
Sharding的管理命令
> db.cmd.findOne(isdbgrid:1);"isdbgrid":1,"hostname":"www.fwphp.cn","ok":1>db.cmd.findOne(isdbgrid:1);"isdbgrid":1,"hostname":"www.fwphp.cn","ok":1>db.cmd.findOne({ismaster:1});
{ "ismaster" : 1, "msg" : "isdbgrid", "ok" : 1 }
> printShardingStatus(db.getSisterDB("config"))
--- Sharding Status ---
sharding version: { "_id" : ObjectId("4b9cd354c33000afad27718d"), "version" : 2 }
shards:
{ "_id" : ObjectId("4b9cd380c33000afad27718e"), "host" : "localhost:27020" }
{ "_id" : ObjectId("4b9cd381c33000afad27718f"), "host" : "localhost:27021" }
databases:
{ "name" : "admin", "partitioned" : false, "primary" : "localhost:27022", "_id" : ObjectId("4b9cd3776693dcfa468dec13") }
my chunks
{ "name" : "user001", "partitioned" : true, "primary" : "localhost:27021", "_id" : ObjectId("4b9cde866693dcfa468dec17") }
my chunks
> use admin
switched to db admin
> db.runCommand({netstat:1})
{ "configserver" : "localhost:27022", "isdbgrid" : 1, "ok" : 1 }
>
参考信息：http://www.mongodb.org/display/DOCS/Sharding
本文转自 不得闲 博客园博客，原文链接：http://www.cnblogs.com/DxSoft/archive/2010/10/21/1857363.html ，如需转载请自行联系原作者
