MongoDB基础（九）分片 - 数据库编程

r> show dbs configsvr> use config configsvr> show collections configsvr> configsvr> db.mongos.find() { "_id" : "mongodb11.kk.net:27016", "ping" : ISODate("2015-05-23T11:16:47.624Z"), "up" : 1221, "waiting" : true, "mongoVersion" : "3.0.2" } configsvr> configsvr> db.shards.find() { "_id" : "shard0000", "host" : "mongodb11.kk.net:27017" } { "_id" : "shard0001", "host" : "mongodb12.kk.net:27018" } { "_id" : "shard0002", "host" : "mongodb13.kk.net:27019" } configsvr> configsvr> db.databases.find() { "_id" : "admin", "partitioned" : false, "primary" : "config" } { "_id" : "mydb", "partitioned" : false, "primary" : "shard0000" } { "_id" : "test", "partitioned" : false, "primary" : "shard0000" }

【4. 对数据库启用分片】

4.1 当前可连接到 mongos 查看数据库或者集合的分片情况（没有分片）：

mongos> db.stats()
mongos> db.tab.stats()

4.2 对数据库激活分片功能：

[root@mongodb11 ~]# mongo 192.168.1.11:27016
mongos> sh.enableSharding("test")

#或者

[root@mongodb11 ~]# mongo 192.168.1.11:27016
mongos> use admin
mongos> db.runCommand( { enableSharding: "test"} )

4.3 此时查看数据库分区情况，partitioned 变为 “true”。

configsvr> use config
switched to db config
configsvr> db.databases.find()
{ "_id" : "admin", "partitioned" : false, "primary" : "config" }
{ "_id" : "mydb", "partitioned" : true, "primary" : "shard0000" }
{ "_id" : "test", "partitioned" : true, "primary" : "shard0000" }

启用数据库分片并没有将数据进行分开，还需要对 collection 进行分片。

【5. 对集合启用分片】

启用前，有几个问题需要考虑的：

1. 选择哪个键列作为 shard key 。（更多参考： Considerations for Selecting Shard Keys）

2. 如果集合中已经存在数据，在选定作为shard key 的键列必须创建索引；如果集合为空，mongodb 将在激活集合分片（sh.shardCollection）时创建索引。

3. 集合分片函数 sh.shardCollection ，

sh.shardCollection(" . ", shard-key-pattern)

mongos> sh.shardCollection("test.tab", { "_id": "hashed" }）

测试：

for (var i=1; i<100000; i++) {
db.kk.insert({"id": i, "myName" : "kk"+i, "myDate" : new Date()});
}

mongos> show collections
mongos> db.kk.find()
mongos> db.kk.createIndex({ "id": "hashed" })
mongos> db.kk.getIndexes()
mongos> sh.shardCollection("test.kk", { "id": "hashed" })
mongos> db.stats()
mongos> db.kk.stats()

由于数据分区需要时间，过会再查看数据分布情况：

总行数：99999

mongos> db.kk.count()
99999

mongos> db.printShardingStatus();
--- Sharding Status --- 
  sharding version: {
	"_id" : 1,
	"minCompatibleVersion" : 5,
	"currentVersion" : 6,
	"clusterId" : ObjectId("556023c02c2ebfdfbc8d39eb")
}
  shards:
	{  "_id" : "shard0000",  "host" : "mongodb11.kk.net:27017" }
	{  "_id" : "shard0001",  "host" : "mongodb12.kk.net:27018" }
	{  "_id" : "shard0002",  "host" : "mongodb13.kk.net:27019" }
  balancer:
	Currently enabled:  yes
	Currently running:  no
	Failed balancer rounds in last 5 attempts:  0
	Migration Results for the last 24 hours: 
		1334 : Success
		2 : Failed with error 'could not acquire collection lock for test.kk to migrate chunk [{ : MinKey },{ : MaxKey }) :: caused by :: Lock for migrating chunk [{ : MinKey }, { : MaxKey }) in test.kk is taken.', from shard0000 to shard0001
  databases:
	{  "_id" : "admin",  "partitioned" : false,  "primary" : "config" }
	{  "_id" : "mydb",  "partitioned" : true,  "primary" : "shard0000" }
	{  "_id" : "test",  "partitioned" : true,  "primary" : "shard0000" }
		test.kk
			shard key: { "id" : "hashed" }
			chunks:
				shard0000	667
				shard0001	667
				shard0002	667
			too many chunks to print, use verbose if you want to force print
	{  "_id" : "events",  "partitioned" : false,  "primary" : "shard0002" }

mongos>

看这里 chunks :
shard0000 667
sha

MongoDB基础（九）分片(二)