The CData ADO.NET Provider for HDFS implements two ADO.NET interfaces you can use to retrieve data from HDFS: HDFSDataAdapter and HDFSDataReader objects. Whereas HDFSDataAdapter objects retrieve a single result set of all the data that matches a query, HDFSDataReader objects fetch data in subset increments as needed.

Using the HDFSDataReader

The HDFSDataReader retrieves data faster than the HDFSDataAdapter because it can retrieve data in pages. As you read data from the HDFSDataReader, it periodically requests the next page of results from the data source, if required. This causes results to be returned at a faster rate. The following example selects all the columns from the Files table:

C#

string connectionString = "Host=sandbox-hdp.hortonworks.com;Port=50070;Path=/user/root;";

using (HDFSConnection connection = new HDFSConnection(connectionString)) {
  HDFSCommand cmd = new HDFSCommand("SELECT * FROM Files", connection);
  
  HDFSDataReader rdr = cmd.ExecuteReader();

  while (rdr.Read()) {
    Console.WriteLine(String.Format("\t{0} --> \t\t{1}", rdr["FileId"], rdr["ChildrenNum"]));
  }
}

VB.NET

Dim connectionString As String = "Host=sandbox-hdp.hortonworks.com;Port=50070;Path=/user/root;"

Using connection As New HDFSConnection(connectionString)
  Dim cmd As New HDFSCommand("SELECT * FROM Files", connection)

  Dim rdr As HDFSDataReader = cmd.ExecuteReader()

  While rdr.Read()
    Console.WriteLine([String].Format(vbTab & "{0} --> " & vbTab & vbTab & "{1}", rdr("FileId"), rdr("ChildrenNum")))
  End While
End Using