详解MongoDB范围片键和哈希片键

1、创建表，只有一个字段name，并插入数据
mongos> use aaa
switched to db aaa
mongos> db.aaa.insert({name:1})
WriteResult({ "nInserted" : 1 })
mongos> db.aaa.insert({name:2})
WriteResult({ "nInserted" : 1 })
mongos> db.aaa.insert({name:3})
WriteResult({ "nInserted" : 1 })
mongos> db.aaa.insert({name:4})
WriteResult({ "nInserted" : 1 })
mongos> 

2、查看数据
mongos> db.aaa.find()
{ "_id" : ObjectId("5fdb7d54d91f2f9bae3b09a1"), "name" : 1 }
{ "_id" : ObjectId("5fdb7d56d91f2f9bae3b09a2"), "name" : 2 }
{ "_id" : ObjectId("5fdb7d59d91f2f9bae3b09a3"), "name" : 3 }
{ "_id" : ObjectId("5fdb7d5cd91f2f9bae3b09a4"), "name" : 4 }

3、允许数据库分片
mongos> sh.enableSharding("aaa")
{
 "ok" : 1,
 "operationTime" : Timestamp(1608220038, 3),
 "$clusterTime" : {
  "clusterTime" : Timestamp(1608220038, 3),
  "signature" : {
   "hash" : BinData(0,"shemm3xvSYrMiy9t7gSYcVtFUuE="),
   "keyId" : NumberLong("6894922308364795934")
  }
 }
}
mongos> 

4、在name字段创建hash索引
mongos> db.aaa.createIndex({name:"hashed"},{background:true})
{
 "raw" : {
  "sharding_yeyz/127.0.0.1:27018,127.0.0.1:27019,127.0.0.1:27020" : {
   "createdCollectionAutomatically" : false,
   "numIndexesBefore" : 1,
   "numIndexesAfter" : 2,
   "ok" : 1
  }
 },
 "ok" : 1,
 "operationTime" : Timestamp(1608220115, 3),
 "$clusterTime" : {
  "clusterTime" : Timestamp(1608220115, 3),
  "signature" : {
   "hash" : BinData(0,"S3Wz9G26eJyOcwa1OLS6TVYu6SE="),
   "keyId" : NumberLong("6894922308364795934")
  }
 }
}

5、以name字段作为片键创建哈希分片
mongos> sh.shardCollection("aaa.aaa",{name:"hashed"})
{
 "collectionsharded" : "aaa.aaa",
 "collectionUUID" : UUID("20a3895e-d821-43ae-9d28-305e6ae03bbc"),
 "ok" : 1,
 "operationTime" : Timestamp(1608220238, 10),
 "$clusterTime" : {
  "clusterTime" : Timestamp(1608220238, 10),
  "signature" : {
   "hash" : BinData(0,"qeQlD3jsSvRZkyamEa2hjbezEdM="),
   "keyId" : NumberLong("6894922308364795934")
  }
 }
}

6、查看分片信息
mongos> db.printShardingStatus()
--- Sharding Status --- 
 sharding version: {
 "_id" : 1,
 "minCompatibleVersion" : 5,
 "currentVersion" : 6,
 "clusterId" : ObjectId("5fafaf4f5785d9965548f687")
 }
 shards:
 { "_id" : "sharding_yeyz", "host" : "sharding_yeyz/127.0.0.1:27018,127.0.0.1:27019,127.0.0.1:27020", "state" : 1 }
 { "_id" : "sharding_yeyz1", "host" : "sharding_yeyz1/127.0.0.1:27024,127.0.0.1:27025,127.0.0.1:27026", "state" : 1 }
 active mongoses:
 "4.0.6" : 1
 autosplit:
 Currently enabled: yes
 balancer:
 Currently enabled: yes
 Currently running: no
 Failed balancer rounds in last 5 attempts: 2
 Last reported error: Could not find host matching read preference { mode: "primary" } for set sharding_yeyz
 Time of Reported error: Wed Nov 18 2020 17:08:14 GMT+0800 (CST)
 Migration Results for the last 24 hours: 
  No recent migrations
 databases:
 { "_id" : "aaa", "primary" : "sharding_yeyz", "partitioned" : true, "version" : { "uuid" : UUID("26e55931-d1c1-4dc5-8a03-b5b0e70f6f43"), "lastMod" : 1 } }
  aaa.aaa
   shard key: { "name" : "hashed" }
   unique: false
   balancing: true
   chunks:
    sharding_yeyz 1
   { "name" : { "$minKey" : 1 } } -->> { "name" : { "$maxKey" : 1 } } on : sharding_yeyz Timestamp(1, 0)