Why XmlReader Usage Pattern Ignores NameTable?

I'm talking about "keep reading till element foo" pattern all we familiar with:

while (reader.Read()) {
  if (reader.NodeType==XmlNodeType.Element && 
    reader.Name=="foo") {
      ...
    }
}

Bolded part is the crux here. reader.Name property returns parsed element name, with respect to the XmlReader's NameTable, while "foo" string doesn't belong to any NameTable. That means usual string comparison (pointers/length/char-by-char) occurs, which is obviously slow. That's not how it was meant to be! "Object Comparison Using XmlNameTable with XmlReader" article of the .NET Framework Developer's Guide suggests different usage pattern:

object cust = reader.NameTable.Add("Customer");
while (reader.Read())
{
   // The "if" uses efficient pointer comparison.
   if (cust == reader.Name)   
   {
      ...
   }
}

Both strings compared here are belong to the same NameTable, thus taking the comparison down to a single cheap pointer comparison!

And what do you think Sun does it in their XML Processing Performance Java and .NET. comparison? The same reader.Name != "LineItemCountValue" stuff! It's interesting to run their tests with such lines fixed.

According to my rough measurements this unfortunate usage pattern costs about 1-20% of the parsing time dependig on many factors. Below is my testing. I'm parsing books.xml document, counting "price" elements. using System; using System.Xml; using System.IO; using System.Runtime.InteropServices; class Class1 { [STAThread] static void Main(string[] args) { StreamReader sr = new StreamReader("books.xml"); string xml = sr.ReadToEnd(); sr.Close(); int num = 1000; PerfTest test = new PerfTest(); Console.WriteLine("Warming up..."); TestWithNoNameTable(xml, num); TestWithNameTable(xml, num); Console.WriteLine("Testing..."); test.Start(); TestWithNameTable(xml, num); Console.WriteLine("Time with NameTable: {0, 6:f2} ms", test.Stop()); test.Start(); TestWithNoNameTable(xml, num); Console.WriteLine("Time with no NameTable: {0, 6:f2} ms", test.Stop()); } public static void TestWithNoNameTable(string xml, int num) { int counter = 0; for (int i=0; i<num; i++) { XmlTextReader r = new XmlTextReader(new StringReader(xml)); while (r.Read()) { if (r.NodeType == XmlNodeType.Element && r.Name.Equals("price")) counter++; } r.Close(); } } public static void TestWithNameTable(string xml, int num) { int counter = 0; XmlNameTable nt = new NameTable(); string key = nt.Get("price"); for (int i=0; i<num; i++) { XmlTextReader r = new XmlTextReader(new StringReader(xml), nt); while (r.Read()) { if (r.NodeType == XmlNodeType.Element && r.Name == key) counter++; } r.Close(); } } } public class PerfTest { [DllImport("kernel32.dll", EntryPoint = "QueryPerformanceCounter", CharSet = CharSet.Unicode)] extern static bool QueryPerformanceCounter(out long perfcount); [DllImport("kernel32.dll", EntryPoint = "QueryPerformanceFrequency", CharSet = CharSet.Unicode)] extern static bool QueryPerformanceFrequency(out long frequency); long startTime; long stopTime; public void Start() { QueryPerformanceCounter(out this.startTime); } public float Stop() { QueryPerformanceCounter(out this.stopTime); long frequency; QueryPerformanceFrequency(out frequency); float diff = (stopTime - startTime); return diff*1000f/(float)frequency; } }

The result on my Win2K box is:

D:\projects\Test\bin\Release>Test.exe
Warming up...
Testing...
Time with NameTable: 1308.86 ms
Time with no NameTable: 1403.60 ms

Benchmarking is a really fragile stuff and I'm sure the results will differ drastically, but basically what I wanted to say is that something needs to be done to fix this particular usage pattern of XmlReader to not ignore great NameTable idea. I encourage fellow MVPs, XmlInsiders and others not to post XmlReader samples, where NameTable is neglected.