Fastest way to copy files from one directory to another

Question

I need to copy files from one directory to another, depending on the existence of the file name in a table of SQL database.

For this I use the following code:

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Answer 1

Since your i/o subsystem is almost certainly the botteneck here, using the parallel task library is probably about as good as it gets:

static void Main(string[] args)
{
  DirectoryInfo source      = new DirectoryInfo( args[0] ) ;
  DirectoryInfo destination = new DirectoryInfo( args[1] ) ;

  HashSet filesToBeCopied = new HashSet( ReadFileNamesFromDatabase() , StringComparer.OrdinalIgnoreCase ) ;

  // you'll probably have to play with MaxDegreeOfParallellism so as to avoid swamping the i/o system
  ParallelOptions options= new ParallelOptions { MaxDegreeOfParallelism = 4 } ;

  Parallel.ForEach( filesToBeCopied.SelectMany( fn => source.EnumerateFiles( fn ) ) , options , fi => {
      string destinationPath = Path.Combine( destination.FullName , Path.ChangeExtension( fi.Name , ".jpg") ) ;
      fi.CopyTo( destinationPath , false ) ;
  }) ;

}

public static IEnumerable ReadFileNamesFromDatabase()
{
  using ( SqlConnection connection = new SqlConnection( "connection-string" ) )
  using ( SqlCommand cmd = connection.CreateCommand() )
  {
    cmd.CommandType = CommandType.Text ;
    cmd.CommandText = @"
      select idPic ,
             namePicFile
      from DocPicFiles
      " ;

    connection.Open() ;
    using ( SqlDataReader reader = cmd.ExecuteReader() )
    {
      while ( reader.Read() )
      {
        yield return reader.GetString(1) ;
      }
    }
    connection.Close() ;

  }
}