CNDBA社区
在之前的博客我们介绍了3节点分片集群的搭建，
MongoDB 4.4 分片集群（3 shard） 搭建手册
https://www.cndba.cn/cndba/dave/article/107970
分片集群在使用之前，需要特别注意，必须先启用sharding，在对集合指定分片键，这个在之前的博客有测试案例：
mongos> sh.enableSharding("cndba")
mongos> sh.shardCollection("cndba.user", { _id : "hashed" } )
如果没有启动sharding或者没有对集合指定分片键，那么新建的库会随机在一个shard上生成，对接的集合也会在该库上创建。
我们这里先创建一张测试表：
mongos> sh.status()
--- Sharding Status ---
sharding version: {
"_id" : 1,
"minCompatibleVersion" : 5,
"currentVersion" : 6,
"clusterId" : ObjectId("62ee1cade37908b0d66ba541")
}
shards:
{ "_id" : "shard1", "host" : "shard1/192.168.56.101:10001,192.168.56.102:10001,192.168.56.103:10001", "state" : 1 }
{ "_id" : "shard2", "host" : "shard2/192.168.56.101:10002,192.168.56.102:10002,192.168.56.103:10002", "state" : 1 }
……
mongos> use cndba
switched to db cndba
mongos> for(var i=1;i<=100000;i++){db.user.save({_id:i,"name":"cndba"})};
测试虚拟机性能有限，提期结束了会话：
mongos> db.user.count()
88034
成功插入了8.8w的数据，新建的库是没有启用sharding功能，现在将单表转成分片。
mongos> db.user.stats()
{
"sharded" : false,
"primary" : "shard2",
"capped" : false,
"wiredTiger" : {
"metadata" : {
"formatVersion" : 1
},
……
mongos> sh.enableSharding("cndba");
{
"ok" : 1,
"operationTime" : Timestamp(1659801295, 7),
"$clusterTime" : {
"clusterTime" : Timestamp(1659801295, 7),
"signature" : {
"hash" : BinData(0,"7ARnLcQXjPVEhp05A43NJdz7/iE="),
"keyId" : NumberLong("7128666789528993815")
}
}
}
mongos>
指定分片键：
mongos> sh.shardCollection("cndba.user", { _id : "hashed" } )
{
"ok" : 0,
"errmsg" : "Please create an index that starts with the proposed shard key before sharding the collection",
"code" : 72,
"codeName" : "InvalidOptions",
"operationTime" : Timestamp(1659801328, 4),
"$clusterTime" : {
"clusterTime" : Timestamp(1659801328, 4),
"signature" : {
"hash" : BinData(0,"nZi/7vtzhXQAoDnxXQi37EF4pig="),
"keyId" : NumberLong("7128666789528993815")
}
}
}
mongos>
这里提示我们创建一个索引：
mongos> db.user.ensureIndex({_id:"hashed"})
{
"raw" : {
"shard2/192.168.56.101:10002,192.168.56.102:10002,192.168.56.103:10002" : {
"createdCollectionAutomatically" : false,
"numIndexesBefore" : 1,
"numIndexesAfter" : 2,
"commitQuorum" : "votingMembers",
"ok" : 1
}
},
"ok" : 1,
"operationTime" : Timestamp(1659801422, 5),
"$clusterTime" : {
"clusterTime" : Timestamp(1659801422, 5),
"signature" : {
"hash" : BinData(0,"76e0gXnINdDM1eX0t+/NynedInA="),
"keyId" : NumberLong("7128666789528993815")
}
}
}
再次对集合分片：
mongos> sh.shardCollection("cndba.user", { _id : "hashed" } )
{
"collectionsharded" : "cndba.user",
"collectionUUID" : UUID("18cf0073-fa77-42ad-971b-71125ee968f6"),
"ok" : 1,
"operationTime" : Timestamp(1659801434, 35),
"$clusterTime" : {
"clusterTime" : Timestamp(1659801434, 35),
"signature" : {
"hash" : BinData(0,"8g5rYYSUFkCED7X0dPqXGkYLsJ0="),
"keyId" : NumberLong("7128666789528993815")
}
}
}
mongos>
查看分片状态：
mongos> db.user.stats()
{
"sharded" : true,
"capped" : false,
"wiredTiger" : {
"metadata" : {
"formatVersion" : 1
},
……
"shards" : {
"shard2" : {
"ns" : "cndba.user",
"size" : 2993156,
"count" : 88034,
"avgObjSize" : 34,
"storageSize" : 1077248,
"freeStorageSize" : 352256,
"capped" : false,
……
此时数据还没有分片。
Mongodb 的数据均衡是启用的：
mongos> sh.getBalancerState()
true
但是并没有运行：
mongos> sh.status()
--- Sharding Status ---
sharding version: {
"_id" : 1,
"minCompatibleVersion" : 5,
"currentVersion" : 6,
"clusterId" : ObjectId("62ee1cade37908b0d66ba541")
}
shards:
{ "_id" : "shard1", "host" : "shard1/192.168.56.101:10001,192.168.56.102:10001,192.168.56.103:10001", "state" : 1 }
{ "_id" : "shard2", "host" : "shard2/192.168.56.101:10002,192.168.56.102:10002,192.168.56.103:10002", "state" : 1 }
active mongoses:
"4.4.16" : 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" : "cndba", "primary" : "shard2", "partitioned" : true, "version" : { "uuid" : UUID("a153446f-4c48-455b-aff9-d12d6c18b58d"), "lastMod" : 1 } }
cndba.user
shard key: { "_id" : "hashed" }
unique: false
balancing: true
chunks:
shard2 1
{ "_id" : { "$minKey" : 1 } } -->> { "_id" : { "$maxKey" : 1 } } on : shard2 Timestamp(1, 0)
{ "_id" : "config", "primary" : "config", "partitioned" : true }
config.system.sessions
shard key: { "_id" : 1 }
unique: false
balancing: true
chunks:
shard1 512
shard2 512
too many chunks to print, use verbose if you want to force print
mongos>
mongos> sh.isBalancerRunning()
false
这里主要是因为我们测试的数据量太小，还没达到迁移的要求。 生产环境会自动启用迁移。 另外均衡器在执行块迁移操作时候会占用实例中节点的资源，对业务多少会有些影响。为了避免块迁移给业务带来影响我们可以设置均衡器的活动窗口，让其在指定的时间段内工作。
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