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

The following example assumes that the field username is the shard key for a collection named users in the myapp database, and that the value smith exists within the range to migrate. Migrate the range using the following command in mongosh.以下示例假设字段username是myapp数据库中名为users的集合的分片键，并且值smith存在于要迁移的范围内。在mongosh中使用以下命令迁移范围。

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

This command moves the range that includes the shard key value "smith" to the shard named mongodb-shard3.example.net. The command will block until the migration is complete.此命令将包含分片键值“smith”的范围移动到名为mongodb-shard3.example.net的分片。该命令将一直阻塞，直到迁移完成。

To evenly migrate ranges for the myapp.users collection, put each prefix range on the next shard from the other and run the following commands in the mongo shell:要均匀迁移myapp.users集合的范围，请将每个前缀范围放在另一个分片的下一个分片上，并在mongo shell中运行以下命令：

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]})
  }
}