随着技術的發展，目前資料庫系統對于海量資料的存儲和高效通路海量資料要求越來越高，MongoDB分片機制就是為了解決海量資料的存儲和高效海量資料通路而生。
MongoDB分片叢集由mongos路由程序（輕量級且非持久化程序）、複制集組成的片shards（分片一般基于複制集故障轉移和備援備份功能）、一組配置伺服器（存儲中繼資料資訊，一般備援3台）構成。
一、部署MongoDB分片叢集
mongod參數可以通過"mongod --help"檢視。
mongos參數可以通過"mongos --help"檢視。
1、配置複制集rs0：
參考文檔：http://www.cnblogs.com/wcwen1990/p/8053860.html
建立rs0複制集資料目錄、日志目錄和配置檔案。
rs0配置檔案：
cat /home/mongodb/db_rs0/config_rs0/rs0.conf
dbpath = /home/mongodb/db_rs0/data/rs0
logpath = /home/mongodb/db_rs0/logs/rs0.log
logappend = true
journal = true
port = 40000
fork = true
maxConns = 5000
bind_ip = 0.0.0.0
replSet = rs0
shardsvr = true
auth = false
2、配置複制集rs1：
參考文檔：http://www.cnblogs.com/wcwen1990/p/8053860.html
建立rs1複制集資料目錄、日志目錄和配置檔案。
rs1配置檔案：
cat /home/mongodb/db_rs1/config_rs1/rs1.conf
dbpath = /home/mongodb/db_rs1/data/rs1
logpath = /home/mongodb/db_rs1/logs/rs1.log
logappend = true
journal = true
port = 40001
fork = true
maxConns = 5000
bind_ip = 0.0.0.0
replSet = rs1
shardsvr = true
auth = false
3、配置configura伺服器，共3台：
configura伺服器也是一個mongod程序，它與我們熟悉的普通mongod程序沒有本質差別，隻是它上面的資料庫和集合存儲的是分片叢集的中繼資料資訊。
建立configura伺服器的資料目錄、日志目錄和配置檔案。
configura配置檔案：
cat /home/mongodb/db_configs/config_cfgserver/cfgserver.conf
dbpath = /home/mongodb/db_configs/data/db_config
logpath = /home/mongodb/db_configs/logs/config.log
logappend = true
port = 40002
maxConns = 5000
bind_ip = 0.0.0.0
replSet = cfgset
configsvr = true
auth = false
fork = true
4、配置路由伺服器：
mongos路由程序功能為整個分片叢集建構一個統一的通路用戶端，使複雜的分片叢集對使用者來說是透明的。上文提到過mongos路由程序是一個輕量級且非持久化的程序，其原因是它不需要像其他程序一樣建立資料目錄dbpath，隻需要建立一個日志目錄即可。
mongos配置檔案内容如下：
cat /home/mongodb/mongos/cfg_mongos.conf
logpath = /home/mongodb/mongos/logs/mongos.log
logappend = true
port = 40003
fork = true
maxConns = 5000
bind_ip = 0.0.0.0
configdb = cfgset/db01:40002,db02:40002,db03:40002
5、分别啟動步驟1、步驟2、步驟3、步驟4配置的9個mongod程序和1個mongos程序：
1）啟動三個rs0複制集：
bin/mongod --config /home/mongodb/db_rs0/config_rs0/rs0.conf
2）啟動三個rs1複制集：
bin/mongod --config /home/mongodb/db_rs1/config_rs1/rs1.conf
3）啟動三個配置伺服器,并且初始化配置伺服器：
bin/mongod --config /home/mongodb/db_configs/config_cfgserver/cfgserver.conf
登入配置伺服器：
bin/mongo --port 40003
執行初始化操作：
rs.initiate({_id:"cfgset",configsvr:true, members:[{_id:1,host:"db01:40002"},{_id:2,host:"db02:40002"},{_id:3,host:"db03:40002"}]})
4）啟動mongos伺服器：
bin/mongos --config /home/mongodb/mongos/cfg_mongos.conf
6、添加各個分片到叢集
上面已經完成了兩個片（複制集）、三個配置伺服器、一個路由伺服器的配置工作。接下來，我們要将各個分片添加到叢集中。
1）打開一個mongo用戶端連接配接mongos伺服器：
bin/mongo --port 40003
2）添加兩個分片到叢集：
sh.addShard("rs0/db01:40000,db02:40000")
sh.addShard("rs1/db01:40001,db02:40001")
3）通過sh.status()檢查上面配置是否正确：
MongoDB Enterprise mongos> sh.status()
--- Sharding Status ---
sharding version: {
"_id" : 1,
"minCompatibleVersion" : 5,
"currentVersion" : 6,
"clusterId" : ObjectId("5a37e16fd7903ab63ab90ebf")
}
shards:
{ "_id" : "rs0", "host" : "rs0/db01:40000,db02:40000", "state" : 1 }
{ "_id" : "rs1", "host" : "rs1/db01:40001,db02:40001", "state" : 1 }
active mongoses:
"3.6.0" : 1
autosplit:
Currently enabled: yes
balancer:
Currently enabled: yes
Currently running: no
Failed balancer rounds in last 5 attempts: 0
Migration Results for the last 24 hours:
No recent migrations
databases:
{ "_id" : "config", "primary" : "config", "partitioned" : true }
4）檢視分片叢集資料庫資訊：
MongoDB Enterprise mongos> show dbs
admin 0.000GB
config 0.000GB
MongoDB Enterprise mongos> db
test
MongoDB Enterprise mongos> use config
switched to db config
MongoDB Enterprise mongos> show collections
changelog
chunks
lockpings
locks
migrations
mongos
shards
tags
transactions
version
至此，MongoDB分片叢集部署成功，生産部署還需要調整一些參數，這部門内容可以通過--help檢視參數詳情。
三、測試MongoDB分片叢集
1、向叢集插入文檔：
MongoDB Enterprise mongos> use chavin
switched to db chavin
MongoDB Enterprise mongos> db.users.insert({userid:1,username:"ChavinKing",city:"beijing"})
WriteResult({ "nInserted" : 1 })
MongoDB Enterprise mongos> db.users.find()
{ "_id" : ObjectId("5a37eabafa5fcca8c960e893"), "userid" : 1, "username" : "ChavinKing", "city" : "beijing" }
2、檢視分片叢集狀态：
MongoDB Enterprise mongos> sh.status()
--- Sharding Status ---
sharding version: {
"_id" : 1,
"minCompatibleVersion" : 5,
"currentVersion" : 6,
"clusterId" : ObjectId("5a37e16fd7903ab63ab90ebf")
}
shards:
{ "_id" : "rs0", "host" : "rs0/db01:40000,db02:40000", "state" : 1 }
{ "_id" : "rs1", "host" : "rs1/db01:40001,db02:40001", "state" : 1 }
active mongoses:
"3.6.0" : 1
autosplit:
Currently enabled: yes
balancer:
Currently enabled: yes
Currently running: no
Failed balancer rounds in last 5 attempts: 0
Migration Results for the last 24 hours:
No recent migrations
databases:
{ "_id" : "chavin", "primary" : "rs1", "partitioned" : false } //資料庫chavin目前不支援分片（"partitioned" : false），資料庫檔案存儲在rs1片上（"primary" : "rs1"）
{ "_id" : "config", "primary" : "config", "partitioned" : true }
config.system.sessions
shard key: { "_id" : 1 }
unique: false
balancing: true
chunks:
rs0 1
{ "_id" : { "$minKey" : 1 } } -->> { "_id" : { "$maxKey" : 1 } } on : rs0 Timestamp(1, 0)
3、MongoDB分片是針對集合的，要想使集合支援分片，首先需要使其資料庫支援分片，為資料庫chavin啟動分片：
MongoDB Enterprise mongos> sh.enableSharding("chavin")
{
"ok" : 1,
"$clusterTime" : {
"clusterTime" : Timestamp(1513614275, 5),
"signature" : {
"hash" : BinData(0,"AAAAAAAAAAAAAAAAAAAAAAAAAAA="),
"keyId" : NumberLong(0)
}
},
"operationTime" : Timestamp(1513614275, 5)
}
4、為分片字段建立索引，同時為集合指定片鍵：
MongoDB Enterprise mongos> db.users.ensureIndex({city:1}) //建立索引
{
"raw" : {
"rs1/db01:40001,db02:40001" : {
"createdCollectionAutomatically" : false,
"numIndexesBefore" : 1,
"numIndexesAfter" : 2,
"ok" : 1
}
},
"ok" : 1,
"$clusterTime" : {
"clusterTime" : Timestamp(1513614344, 1),
"signature" : {
"hash" : BinData(0,"AAAAAAAAAAAAAAAAAAAAAAAAAAA="),
"keyId" : NumberLong(0)
}
},
"operationTime" : Timestamp(1513614344, 1)
}
MongoDB Enterprise mongos> sh.shardCollection("chavin.users",{city:1}) //啟用集合分片，為其指定片鍵
{
"collectionsharded" : "chavin.users",
"collectionUUID" : UUID("a5de7086-115c-44a3-984e-3db8d945dbab"),
"ok" : 1,
"$clusterTime" : {
"clusterTime" : Timestamp(1513614387, 13),
"signature" : {
"hash" : BinData(0,"AAAAAAAAAAAAAAAAAAAAAAAAAAA="),
"keyId" : NumberLong(0)
}
},
"operationTime" : Timestamp(1513614387, 13)
}
5、再次檢視分片叢集狀态：
MongoDB Enterprise mongos> sh.status()
--- Sharding Status ---
sharding version: {
"_id" : 1,
"minCompatibleVersion" : 5,
"currentVersion" : 6,
"clusterId" : ObjectId("5a37e16fd7903ab63ab90ebf")
}
shards:
{ "_id" : "rs0", "host" : "rs0/db01:40000,db02:40000", "state" : 1 }
{ "_id" : "rs1", "host" : "rs1/db01:40001,db02:40001", "state" : 1 }
active mongoses:
"3.6.0" : 1
autosplit:
Currently enabled: yes
balancer:
Currently enabled: yes
Currently running: no
Failed balancer rounds in last 5 attempts: 0
Migration Results for the last 24 hours:
No recent migrations
databases:
{ "_id" : "chavin", "primary" : "rs1", "partitioned" : true } //此時chavin資料庫已經支援分片
chavin.users
shard key: { "city" : 1 }
unique: false
balancing: true
chunks:
rs1 1
{ "city" : { "$minKey" : 1 } } -->> { "city" : { "$maxKey" : 1 } } on : rs1 Timestamp(1, 0) //目前存在一個片，存儲在rs1上
{ "_id" : "config", "primary" : "config", "partitioned" : true }
config.system.sessions
shard key: { "_id" : 1 }
unique: false
balancing: true
chunks:
rs0 1
{ "_id" : { "$minKey" : 1 } } -->> { "_id" : { "$maxKey" : 1 } } on : rs0 Timestamp(1, 0)
6、向叢集插入測試資料：
MongoDB Enterprise mongos> for(var i=1;i<1000000;i++) db.users.insert({userid:i,username:"chavin"+i,city:"beijing"})
MongoDB Enterprise mongos> for(var i=1;i<1000000;i++) db.users.insert({userid:i,username:"dbking"+i,city:"changsha"})
7、再次檢視分片叢集狀态：
MongoDB Enterprise mongos> sh.status()
--- Sharding Status ---
sharding version: {
"_id" : 1,
"minCompatibleVersion" : 5,
"currentVersion" : 6,
"clusterId" : ObjectId("5a37e16fd7903ab63ab90ebf")
}
shards:
{ "_id" : "rs0", "host" : "rs0/db01:40000,db02:40000", "state" : 1 }
{ "_id" : "rs1", "host" : "rs1/db01:40001,db02:40001", "state" : 1 }
active mongoses:
"3.6.0" : 1
autosplit:
Currently enabled: yes
balancer:
Currently enabled: yes
Currently running: no
Failed balancer rounds in last 5 attempts: 0
Migration Results for the last 24 hours:
1 : Success
databases:
{ "_id" : "chavin", "primary" : "rs1", "partitioned" : true }
chavin.users
shard key: { "city" : 1 }
unique: false
balancing: true
chunks:
rs0 1
rs1 2
{ "city" : { "$minKey" : 1 } } -->> { "city" : "beijing" } on : rs0 Timestamp(2, 0) //分片1，存儲在rs0中，并且标注了範圍
{ "city" : "beijing" } -->> { "city" : "guangdong" } on : rs1 Timestamp(2, 1) //分片2，存儲在rs1中，并且标注了範圍
{ "city" : "guangdong" } -->> { "city" : { "$maxKey" : 1 } } on : rs1 Timestamp(1, 3) //分片3，存儲在rs1中，并且标注了範圍
{ "_id" : "config", "primary" : "config", "partitioned" : true }
config.system.sessions
shard key: { "_id" : 1 }
unique: false
balancing: true
chunks:
rs0 1
{ "_id" : { "$minKey" : 1 } } -->> { "_id" : { "$maxKey" : 1 } } on : rs0 Timestamp(1, 0)
8、更加詳細的分析需要從集合changelog入手分析：
db.changelog.find()可以檢視到具體的動作資訊，這裡不再贅述。
