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VTD-XML Investigation

VTD-XML ( is a high-performance XML processing model that deals with XML in a binary form, instead of the traditional text form. VTD stands for Virtual Token Descriptor.

VTD-XML parses an XML document and builds an internal data structure representing the entire XML document in byte[] form. Each "token" of the XML document is represented as the following 64-bit integer:

Vtd layout.jpg

  • Big endian
  • Starting offset: 30 bits (b29 ~ b0) maximum value is 2^30 -1 = 1G -1
  • Length: 20 bits (b51 ~ b32) maximum value is 2^20-1 = 1M -1
    • For some token type
      • Prefix length: 9 bits (b51~ b43) max value 511
      • Q-name length: 11 bits (b42 ~ b 32) max value 1023
  • Depth: 8 bits (b59~b52) max value is 2^8-1 = 255
  • Token type: 4 bits (b63~b60)
  • Reserved bit: 2 bits (b31: b30)

VTD-XML Core Concepts

Generating a VTD-XML Representation of the XML Document (Unmarshal)

VTDGen vg = new VTDGen();
// from existing byte[]
// true indicates namespace aware
vg.setDoc(byte[]); vg.parse(true);
// - or - 
// from file
vg.parseFile("old.xml", false)

Writing a VTD-XML Document (Marshal)

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