[Pnet-developers] XmlTextReader performance problems and ResX

[Marcus]

In another email, I reported that I was debugging ResXResourceReader. This 
class reads .resx files, which are in XML format.  Items such as bitmaps can 
be embedded in the .resx files, so they can be quite large. 
ResXResourceReader uses the XmlTextReader class to read the file. After 
fixing these bugs, I can actually read resource files with the class. 
However, I discovered that my test app was getting bogged down in the 
XmlTextReader.ReadElementString().

I wrote a standalone test that reads an XML file that contains an element with 
a large amount of text, similar to that in a .resx file. I experimented with 
various sizes of the data and discovered that the time required to read the 
element string was O(n^2). (For example, approx 1006 lines took 3 seconds, 
2000 took 11, 5000 took 63, and 10000 took 251.)

I cannot tell why the time required is increasing quadratically. The number of 
calls to the "hot" (frequently-called) methods only increases linearly (see 
below).

"Hot" methods for 1000 lines:

  178920    instance bool 
System.Xml.Private.XmlParserInput::EnsureCapacity(int32)
   99606    instance int32 System.Text.StringBuilder::AppendSpace(int32)
   99599    void System.String::CharFill(class System.String, int32, int32, 
char)
   99599    instance class System.Text.StringBuilder 
System.Text.StringBuilder::Append(char)
   89469    instance bool System.Xml.Private.XmlParserInput::PeekChar()
   89451    instance bool System.Xml.Private.XmlParserInput::NextChar()
   89451    instance void 
System.Xml.Private.XmlParserInputBase/LogManager::Append(char)
    7255    class System.String System.String::NewBuilder(class System.String, 
int32)
    6683    instance class System.String 
System.Text.StringBuilder::NewBuilder(class System.String, int32)
    4233    instance int32 System.String::get_Length()


"Hot" methods for 2000 lines:

  357098    instance bool 
System.Xml.Private.XmlParserInput::EnsureCapacity(int32)
  188695    instance int32 System.Text.StringBuilder::AppendSpace(int32)
  188688    void System.String::CharFill(class System.String, int32, int32, 
char)
  188688    instance class System.Text.StringBuilder 
System.Text.StringBuilder::Append(char)
  178558    instance bool System.Xml.Private.XmlParserInput::PeekChar()
  178540    instance bool System.Xml.Private.XmlParserInput::NextChar()
  178540    instance void 
System.Xml.Private.XmlParserInputBase/LogManager::Append(char)
  10039    class System.String System.String::NewBuilder(class System.String, 
int32)
    9467    instance class System.String 
System.Text.StringBuilder::NewBuilder(class System.String, int32)
    4233    instance int32 System.String::get_Length()