Merging XML files

[pbb72]

I need to merge a huge amount of XML files into one. The files all have the following structure:

<!DOCTYPE ...>
<FILE>
  <REC ...>
    <FLD ...>...</FLD>
    ...
  </REC>
  ...
</FILE>

I've written the following code to do this:

private void btnOpen_Click(object sender, EventArgs e)
{
  if (openFileDialog1.ShowDialog() != DialogResult.OK) return;
  progressBar1.Maximum = openFileDialog1.FileNames.Length;
  XmlReaderSettings xmlsetting = new XmlReaderSettings();
  xmlsetting.ProhibitDtd = false;
  DataSet ds = new DataSet();
  DataSet dsDest = new DataSet();
  XmlReader xmlread;
  foreach (string s in openFileDialog1.FileNames)
  {
    xmlread = XmlReader.Create(s, xmlsetting);
    ds.Clear();
    ds.ReadXml(xmlread);
    dsDest.Merge(ds);
    xmlread.Close();
    progressBar1.Value++;
  }
  if (saveFileDialog1.ShowDialog() != DialogResult.OK) return;
  dsDest.WriteXml(saveFileDialog1.FileName);
}

I have two problems with my code:

1. Memory usage: on a small testrun, the application used 500MB memory for a merged XML file of 80MB. Do I have a big memory leak, or is this to be expected for such huge amounts of XML data?

2. The resulting file misses the <!DOCTYPE> and has an added level above <FILE> called <NewDataSet>. How do I add the <!DOCTYPE> and remove the <NewDataSet> from the resulting XML?

Thanks, Peter