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Posted 20 Nov 2008


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Split large XML files into small files

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9 Jan 2012CPOL2 min read
Read any size XML docuement and split it into small supporting files.

Image 1

Fig. 1


Working with large XML files is not always an easy task. I am referring to files of size 25MB and more. An approach for processing such large XML files may be to split the XML document into smaller files for processing. It is a no brainier if you just want to split a file into multiple files, but what if you need this partial file to be accessible by an XML parser or DOM individually? You need to make sure that you have a complete node at the end of your smaller file, and you want to skip to the next node at the beginning of your next file.


This is the continuation of my previous topic on how to deal with large XML documents: Large XML Files Processing and Indexing.

Using the code

Here is an idea of how you can do it. I tested the code with many different XML files and it works for the majority of XML files. You may get an error if your split size is too small. It also depends on your XML formatting.

Try to use the attached XML document as an example. Also, I have attached the results of this process: the files .part1, .part2, .part3.

Here is how we split the file and how it works:

  • Run the EXE as in Fig. 1.
  • Select a file to split (a large XML file).
  • Fig2.JPG

    Now split the file: get the XML file first. Call ImportXMLDoc(false);SplitFile();.

/// <summary>
/// Split file based on max size in MB
/// </summary>
private void SplitFile() {
    if (string.IsNullOrEmpty(filePath)) {
        MessageBox.Show("Select XML File to split");

    FileInfo fi = new FileInfo(filePath);
    double origFileSize = (double)fi.Length;
    numOfNewFiles = Math.Ceiling(origFileSize / maxFileSplitSize);
    string filePart = Application.StartupPath + "/" + fi.Name + 
                      ".part1" + fi.Extension;
    int fileCnt = 1;
    long writeFilePosition = 0;

    using (StreamReader sr = new StreamReader(filePath, Encoding.UTF8)) {
        int pos = 0;
        filePart = Application.StartupPath + "/" + fi.Name + 
                   ".part" + fileCnt + fi.Extension;
        //Read each line in XML document as regular file stream.
        StreamWriter sw = new StreamWriter(filePart, false);

        Regex rx = new Regex(@"<", RegexOptions.Compiled | 
        string nodeName = string.Empty;
        do {

            string line = sr.ReadLine();
            pos += Encoding.UTF8.GetByteCount(line) + 2;
            // 2 extra bites for end of line chars.

            MatchCollection m = rx.Matches(line);
            //Save index of this node into dictionary
            foreach (Match mt in m) {
                nodeName = line.Split(' ').Length == 0 ? 
                           line.Substring(1, line.LastIndexOf('>') - 1) : 
                           line.Split(new char[] { ' ' }, 
                if (!nodeName.Contains("?xml") && 
                    !nodePathDic.ContainsKey(pos + mt.Index)) {
                    nodePathDic.Add(pos + mt.Index, nodeName);

            writeFilePosition = sw.BaseStream.Position;

            //If we at the limit of new file let's get 
            //a last node and write it to this file 
            //and create a new split file.
            if (pos > maxFileSplitSize * fileCnt) {
                int lastNodeStartPosition = 0;
                string lastNodeName = string.Empty;
                string ln = string.Empty;
                string completeLastNode = GetLastNode(filePath, 
                       out lastNodeStartPosition, out lastNodeName);

                //Some synchronization. TODO: needs to be optimized 
                //but it works "AS IS"
                do {
                    //Skip rest of the node....
                    ln = sr.ReadLine();
                    if (ln == null)

                    pos += Encoding.UTF8.GetByteCount(ln) + 2;
                } while (!ln.Contains(lastNodeName));

                //Get position where we will begin to read again in our 
                //original XML file. We want to skip to the end of last 
                //complete node we wrote to the file.
                long swPosition = (writeFilePosition - 
                                  (nodePathDic.Keys[nodePathDic.Count - 1] - 
                                   lastNodeStartPosition)) + 2;
                sw.BaseStream.Position = swPosition >= 0 ? swPosition : 0;
                sw.WriteLine("<!-- End of " + Application.StartupPath + "/" + 
                             fi.Name + ".part" + fileCnt + fi.Extension + ". " + 
                             fileCnt + " out of " + numOfNewFiles + " -->");

                sw.WriteLine(completeLastNode + "\n\n");
                sw.WriteLine(nodePathDic.Values[0].Replace("<", "</"));

                filePart = Application.StartupPath + "/" + fi.Name + 
                           ".part" + (++fileCnt) + fi.Extension;

                sw = new StreamWriter(filePart, false);
                sw.WriteLine("<!-- Start of " + Application.StartupPath + "/" + 
                             fi.Name + ".part" + fileCnt + fi.Extension + ". " + 
                             fileCnt + " out of " + numOfNewFiles + " -->");
        } while (!sr.EndOfStream);

        //Clean up...


At the end of the run, you should have the files included in a Zip file.


Let’s take a look at the output of this process:

At the end of each file, note the “<!—End of…." comment line and the complete last node. I added this for a visual effect. I can use it later to join the documents together (that would be in my next article).


The next file will start where the last file ended.



Root nodes are at the beginning and at the end of each document. The output XML file should be good to be used in an XML DOM or a tool like XMLSpy.

Enjoy. If you have any questions, post them here or send me an email.


  • Created on November 20, 2008.
  • Jan 09, 2011: I've changed the logic of how to end the file nodes and start new file nodes. This is a more robust version and based on .NET 4.0 and includes xsd.exe to generate the XML file schema.


This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)


About the Author

Slava Khristich
Software Developer (Senior) Tateeda Media Networks
United States United States

Software development is my passion as well as photography.

If you got a sec stop by to see my photography work at

Tateeda Media Network

Comments and Discussions

QuestionI modified this to enter tag name and count. Pin
webmonkeymon2-Apr-20 7:04
Memberwebmonkeymon2-Apr-20 7:04 
QuestionFileNotFoundException Error Pin
Member 1347509111-Oct-18 12:18
MemberMember 1347509111-Oct-18 12:18 
Questionplease help Pin
Member 1194643130-Aug-15 16:32
MemberMember 1194643130-Aug-15 16:32 
BugSpecial Char Read or Write Pin
Ageng Dwi Prastyawan22-Mar-14 9:32
MemberAgeng Dwi Prastyawan22-Mar-14 9:32 
QuestionSplit 8GB xml file Pin
el0769428-Nov-13 1:47
Memberel0769428-Nov-13 1:47 
AnswerRe: Split 8GB xml file Pin
Member 174238123-Jan-14 20:29
MemberMember 174238123-Jan-14 20:29 
QuestionXML source that DOES NOT have newline characters Pin
Anthony Concialdi2-Dec-11 11:42
MemberAnthony Concialdi2-Dec-11 11:42 
QuestionCode Pin
Lisa121130-Nov-11 9:31
MemberLisa121130-Nov-11 9:31 
AnswerRe: Code Pin
Slava Khristich30-Nov-11 15:42
MemberSlava Khristich30-Nov-11 15:42 
GeneralRe: Code Pin
Slava Khristich1-Dec-11 5:37
MemberSlava Khristich1-Dec-11 5:37 
GeneralRe: Code Pin
Lisa121128-Dec-11 11:01
MemberLisa121128-Dec-11 11:01 
Questionswdish signs converts to junk Pin
Member 842483222-Nov-11 10:04
MemberMember 842483222-Nov-11 10:04 
AnswerRe: swdish signs converts to junk Pin
Slava Khristich28-Dec-11 12:50
MemberSlava Khristich28-Dec-11 12:50 
QuestionUnable to find a version of the runtime to run this application Pin
thomasKreiller7-Sep-11 12:50
MemberthomasKreiller7-Sep-11 12:50 
AnswerRe: Unable to find a version of the runtime to run this application Pin
Slava Khristich7-Sep-11 14:12
MemberSlava Khristich7-Sep-11 14:12 
QuestionHow to split 3GB xml file? Pin
sophie12282-Sep-11 9:29
Membersophie12282-Sep-11 9:29 
AnswerRe: How to split 3GB xml file? Pin
Slava Khristich7-Sep-11 14:09
MemberSlava Khristich7-Sep-11 14:09 
GeneralMy vote of 1 Pin
gonzalovm120-Jul-11 11:20
Membergonzalovm120-Jul-11 11:20 
AnswerRe: My vote of 1 Pin
Slava Khristich26-Jul-11 6:52
MemberSlava Khristich26-Jul-11 6:52 
Generalxml splitter Pin
yosiasz25-Mar-11 8:24
Memberyosiasz25-Mar-11 8:24 
GeneralRe: xml splitter Pin
Slava Khristich25-Mar-11 9:24
MemberSlava Khristich25-Mar-11 9:24 
Generalunable to find nodePathDic declration and GetLstNode function Pin
anilkg2y9-Sep-10 19:08
Memberanilkg2y9-Sep-10 19:08 
GeneralExactly what I was looking for, but a small issue, OutOfMemoryException Pin
LordAshcroft29-Dec-09 13:11
MemberLordAshcroft29-Dec-09 13:11 
Generalvtd-xml is ideally suited for splitting xml doc Pin
Jimmy Zhang21-Nov-09 13:03
MemberJimmy Zhang21-Nov-09 13:03 
GeneralNested XML Pin
John Norrby11-Nov-09 0:15
MemberJohn Norrby11-Nov-09 0:15 

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