Create Ranges in a Sharded Cluster在分片群集中创建范围

In most situations a sharded cluster will create, split, and distribute ranges automatically without user intervention. 在大多数情况下，分片集群将自动创建、分割和分配范围，而无需用户干预。However, in some cases, MongoDB cannot create enough ranges or distribute data fast enough to support the required throughput.然而，在某些情况下，MongoDB无法创建足够的范围或快速分发数据以支持所需的吞吐量。

For example, if you want to ingest a large volume of data into a cluster where you have inserts distributed across shards, pre-splitting the ranges of an empty sharded collection can improve throughput.例如，如果你想将大量数据摄入到一个集群中，在这个集群中，插入分布在多个分片上，预先分割空分片集合的范围可以提高吞吐量。

Alternatively, by defining the zones and zone ranges before sharding an empty or a non-existing collection, the shard collection operation creates ranges for the defined zone ranges as well as any additional ranges to cover the entire range of the shard key values and performs an initial range distribution based on the zone ranges. 或者，通过在对空或不存在的集合进行分片之前定义区域和区域范围，分片集合操作为定义的区域范围以及任何其他范围创建范围，以覆盖分片键值的整个范围，并根据区域范围执行初始范围分布。For more information, see Empty Collection.有关更多信息，请参阅空集合。

// Generate two character prefix email ranges.
function getRanges(shards) {
   let ranges = [];

   // The total number of prefix possibilities is 26 * 26 (aa to zz).
   // We calculate the number of combinations to add in a range.
   const totalCombinationsPerShard = 26 * 26 / shards.length;
   let minKey = {
      email: MinKey
   };
   let maxKey = {
      email: MinKey
   };

   for(let i = 1; i <= shards.length; ++i) {
      // 97 is lower case 'a' in ASCII.
      let prefix = 97 + ((totalCombinationsPerShard*i)/26);
      let suffix = 97 + ((totalCombinationsPerShard*i)%26);
      let initialChars = String.fromCharCode(prefix) + String.fromCharCode(suffix);

      minKey = maxKey;
      maxKey = {
         email: i !== shards.length ? initialChars : MaxKey
      };

      ranges.push({
         min: minKey,
         max: maxKey
      });
   }

   return ranges;
}

db.adminCommand( {
   shardCollection: 'sample.documents',
   key: {
      email: 1
   }
} );

const shards = db.adminCommand({
   listShards: 1
}).shards;

let ranges = getRanges(shards);

for (let i = 0; i < ranges.length; ++i) {
   db.adminCommand({
      moveRange: 'sample.documents',
      min: ranges[i].min,
      max: ranges[i].max,
      toShard: shards[i]._id
   });
}