Migrate Ranges in a Sharded Cluster

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.

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.

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:

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]})
  }
}