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我们在 sharded mongo 环境中进行了模拟测试，但是如果 shard key 值为 small int，则集合没有分发，但如果 shard key 为 big int，则工作正常。请继续阅读...

用于从 mongos shell 插入记录的代码。

var shId = 15;
for (var i = 0; i < 100; i++) {
  if(i%50 == 0){
      shId = shId + 1;
  }
  db.Foo.insert( { shKeyId : shId , text:"this is a test" } );
}

使用 shId = 15，Foo 集合拆分为两个分片不起作用。

环境：两个分片，每个分片具有 Primary1 和两个辅助 mongod 实例。Mongo 配置正在其中一个分片上运行。

通过 shKeyId 对 'Foo' 集合启用分片作为散列分片键。db.runCommand({ shardcollection : "test.Foo", key : {shKeyId : "hashed"}});

sh.status() 输出

mongos> sh.status();
--- Sharding Status --- 
  sharding version: {
    "_id" : 1,
    "version" : 3,
    "minCompatibleVersion" : 3,
    "currentVersion" : 4,
    "clusterId" : ObjectId("516ea48e979736fd306973c9")
}
  shards:
    {  "_id" : "mongo-perf-shrd1",  "host" : "mongo-perf-shrd1/sh1-prim-ip:27017,sh1-sec1-ip:27017,sh1-sec2-ip:27017" }
    {  "_id" : "mongo-perf-shrd2",  "host" : "mongo-perf-shrd2/sh2-prim-ip:27017,sh2-sec1-ip:27017,sh2-sec2-ip:27017" }
  databases:
    {  "_id" : "admin",  "partitioned" : false,  "primary" : "config" }

    {  "_id" : "test",  "partitioned" : true,  "primary" : "mongo-perf-shrd2" }
        test.Foo
            shard key: { "shKeyId" : "hashed" }
            chunks:
                mongo-perf-shrd2    2
                mongo-perf-shrd1    2
            { "shKeyId" : { "$minKey" : 1 } } -->> { "shKeyId" : NumberLong("-4611686018427387902") } on : mongo-perf-shrd2 { "t" : 2, "i" : 2 } 
            { "shKeyId" : NumberLong("-4611686018427387902") } -->> { "shKeyId" : NumberLong(0) } on : mongo-perf-shrd2 { "t" : 2, "i" : 3 } 
            { "shKeyId" : NumberLong(0) } -->> { "shKeyId" : NumberLong("4611686018427387902") } on : mongo-perf-shrd1 { "t" : 2, "i" : 4 } 
            { "shKeyId" : NumberLong("4611686018427387902") } -->> { "shKeyId" : { "$maxKey" : 1 } } on : mongo-perf-shrd1 { "t" : 2, "i" : 5 }

分片分布输出

   mongos> db.Foo.getShardDistribution();

Shard mongo-perf-shrd1 at mongo-perf-shrd1/ip1:27017,ip2,ip3:27017
 data : 6KiB docs : 100 chunks : 2
 estimated data per chunk : 3KiB
 estimated docs per chunk : 50

Shard mongo-perf-shrd2 at mongo-perf-shrd2/ip4:27017,ip5:27017,ip6:27017
 data : 0B docs : 0 chunks : 2
 estimated data per chunk : 0B
 estimated docs per chunk : 0

Totals
 data : 6KiB docs : 100 chunks : 4
 Shard mongo-perf-shrd1 contains 100% data, 100% docs in cluster, avg obj size on shard : 64B
 Shard mongo-perf-shrd2 contains 0% data, 0% docs in cluster, avg obj size on shard : NaNGiB
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1 回答 1

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你只有单调的分片键，这不是好的解决方案： http: //docs.mongodb.org/manual/core/sharded-cluster-internals/

对于刚刚模拟测试，足以默认选择 _id 字段的分片键

于 2013-04-17T10:13:47.103 回答