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MongoDB分片

分片（sharding）是将数据拆分，将其分散在不同的机器上的过程。MongoDB支持自动分片

片键（shard
key）设置分片时，需要从集合里面选一个键，用该键作为数据拆分的依据，此键就叫片键

分片一般有以下三部分组成：

片     可以是普通的mongod进程，也可以是副本集。

但是即使一片内有多台服务器，也只能有一个主服务器，其他的服务器保存相同的数据

         Mongos

                  就是mongodb的路由器进程，它路由所有请求，然后将结果聚合。它不保存存储数据或配置信息

                   它本身并不存储数据或配置信息（但会缓存配置服务器信息）

         配置服务器

                   存储集群的配置信息：数据和片的对应关系

                   Mongos不会永久存放数据,所以需要个地方存放分片配置

环境规划

创建db|logpath目录

~]# mkdir /data/mongodb/conf /data/mongodb/shard{1,2}

~]# mkdir /data/mongodb/logs/

启动配置服务

#配置服务器要最先启动，因为mongos会用它其上的配置信息

~]# mongod --dbpath /data/mongodb/conf --logpath /data/mongodb/logs/conf.log --logappend --fork --port 10000

about to fork child process, waiting until server is ready for connections.

forked process: 14234

child process started successfully, parent exiting

启动路由服务

#mongos进程不需要数据目录

~]# mongos --port 20000 --configdb 192.168.211.217:10000 --logpath /data/mongodb/logs/mongos.log  --logappend --fork

2015-01-15T17:21:13.758+0800 warning: running with 1 config server should be done only for testing purposes and is not recommended for production

about to fork child process, waiting until server is ready for connections.

forked process: 15361

child process started successfully, parent exiting

启动分片服务

~]#mongod --fork --dbpath /data/mongodb/shard1 --logpath /data/mongodb/logs/shard1.log --logappend -port 30000

about to fork child process, waiting until server is ready for connections.

forked process: 15426

child process started successfully, parent exiting

~]#mongod --fork --dbpath /data/mongodb/shard2 --logpath /data/mongodb/logs/shard2.log --logappend -port 40000

about to fork child process, waiting until server is ready for connections.

forked process: 15515

child process started successfully, parent exiting

添加分片

#查看mongos的端口

~]# netstat  -ntpl|grep mongos

tcp        0      0 0.0.0.0:20000               0.0.0.0:*                  
LISTEN      15361/mongos

#连接刚才启动的mongos（192.168.211.217:20000）

~]# /usr/local/mongodb/bin/mongo --port 20000

MongoDB shell version: 2.6.6

connecting to: 127.0.0.1:20000/test

mongos了mongos> use
admin

switched to db admin

mongos> db.runCommand({addshard:"192.168.211.217:30000",allowLocal:true })

{ "shardAdded" : "shard0000", "ok" : 1 }

mongos> db.runCommand({addshard:"192.168.211.217:40000",allowLocal:true })

{ "shardAdded" : "shard0001", "ok" : 1 }

注：allowLocal:true当路由进程和分片在同一台机器上要指定allowLocal为true

mongos进程

mongos> use config

switched to db config

mongos> db.shards.find()

{ "_id" : "shard0000", "host" : "192.168.211.217:30000" }

{ "_id" : "shard0001", "host" : "192.168.211.217:40000" }

切分数据

默认的是不会将存储的每条数据进行分片处理，需要在数据库和集合的粒度上都开启分片功能

test库的分片功能#连接emp集合#对集合进行分片（

mongos> use admin

switched to db admin

mongos> db.runCommand({"shardcollection":"test.emp","key":{"_id":1}})

{ "collectionsharded" : "test.emp", "ok" : 1 }

mongos> use config

switched to db config

mongos> db.databases.find()

{ "_id" : "admin", "partitioned" : false, "primary" : "config" }

{ "_id" : "test", "partitioned" : true, "primary" : "shard0000" }

true则表示开启了分片功“primary”，字符串。这个值与“大本营

mongos> db.collections.find()

{ "_id" : "test.emp", "lastmod" : ISODate("2015-01-15T09:48:49.919Z"), "dropped" : false, "key" : { "_id" : 1 }, "unique" : false, "lastmodEpoch" : ObjectId("54b78d0167f270682893cda6")
}

mongos> db.chunks.find()

{ "_id" : "test.emp-_id_MinKey", "lastmod" : Timestamp(1, 0), "lastmodEpoch" : ObjectId("54b78d0167f270682893cda6"), "ns" : "test.emp", "min" : { "_id" : { "$minKey" : 1 } }, "max" : {
"_id" : { "$maxKey" : 1 } }, "shard" : "shard0000" }

emp集合就按照“_id”片键分散到各个片上                       
{ "_id" : { "$minKey" : 1 } } -->> { "_id" : { "$maxKey" : 1 } } on : shard0000 Timestamp(1, 0)