Migrate Ranges in a Sharded Cluster迁移分片群集中的范围

In most circumstances, you should let the automatic balancer migrate ranges between shards. However, you may want to migrate ranges manually in a few cases:在大多数情况下，应该让自动平衡器在分片之间迁移范围。但是，在以下几种情况下，您可能需要手动迁移范围：

• When pre-splitting an empty collection, migrate ranges manually to distribute them evenly across the shards. 预拆分空集合时，请手动迁移范围，以便将它们均匀地分布在分片上。Use pre-splitting in limited situations to support bulk data ingestion.在有限的情况下使用预拆分来支持批量数据接收。
• If the balancer in an active cluster cannot distribute ranges within the balancing window, then you will have to migrate ranges manually.如果活动集群中的平衡器无法在平衡窗口内分配范围，则必须手动迁移范围。

To manually migrate ranges, use the moveChunk or moveRange command.要手动迁移范围，请使用moveChunk或moveRange命令。

For more information on how the automatic balancer moves ranges between shards, see Balancer Internals and Range Migration.有关自动平衡器如何在分片之间移动范围的更多信息，请参阅平衡器内部和范围迁移。

For more information on tuning the migration, see chunkMigrationConcurrency.有关调整迁移的更多信息，请参阅chunkMigrationConcurrency。

db.adminCommand( { moveChunk : "myapp.users",
                   find : {username : "smith"},
                   to : "mongodb-shard3.example.net" } )

var shServer = [ "sh0.example.net", "sh1.example.net", "sh2.example.net", "sh3.example.net", "sh4.example.net" ];
for ( var x=97; x<97+26; x++ ){
  for( var y=97; y<97+26; y+=6 ) {
    var prefix = String.fromCharCode(x) + String.fromCharCode(y);
    db.adminCommand({moveChunk : "myapp.users", find : {email : prefix}, to : shServer[(y-97)/6]})
  }
}

See Create Ranges in a Sharded Cluster for an introduction to pre-splitting.有关预拆分的介绍，请参阅在分片群集中创建范围。

• Use the moveRange command with the _secondaryThrottle and writeConcern fields to determine when the balancer proceeds with the next document in the migrating range.将moveRange命令与_secondaryThrottle和writeConcern字段一起使用，以确定平衡器何时继续迁移范围中的下一个文档。
• Use the moveRange command with the secondaryThrottle and writeConcern fields to determine when the balancer proceeds with the next document in the migrating range.将moveRange命令与secondaryThrottle和writeConcern字段一起使用，以确定平衡器何时继续迁移范围中的下一个文档。

See moveRange and moveRange for details.有关详细信息，请参阅moveRange和moveRange。