PHP Extension

Efficiently Process a Huge XML File

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Demonstrates a technique for processing a huge XML file (can be any size, even many gigabytes).

Note: This example requires Chilkat v9.5.0.80 or greater.

PHP Extension

<?php

include("chilkat.php");

$success = false;

// This example shows a way to efficiently process a gigantic XML file -- one that may be too large
// to fit in memory.  
// 
// Two types of XML parsers exist: DOM parsers and SAX parsers.

// A DOM parser is a Document Object Model parser, where the entire XML is loaded into memory
// and the application has the luxury of interacting with the XML in a convenient, random-access
// way.  The Chilkat Xml class is a DOM parser.  Because the entire XML is loaded into memory,
// huge XML files (on the order of gigabytes) are usually not loadable for memory constraints.

// A SAX parser is such that the XML file is parsed as an input stream.  No DOM exists.  
// Using a SAX parser is generally less palatable than using a DOM parser, for many reasons.
// 
// The technique described here is a hybrid.  It streams the XML file as unstructured text
// to extract fragments that are individually treated as separate XML documents loaded into
// the Chilkat Xml parser.
// 
// For example, imagine your XML file is several GBs in size, but has a relatively simple structure, such as:
// 
// <Transactions>
//     <Transaction id="1">
//          ...
//     </Transaction>
//     <Transaction id="2">
//          ...
//     </Transaction>
//     <Transaction id="3">
//          ...
//     </Transaction>
// ...
// </Transactions>

// In the following code, each <Transaction ...> ... </Transaction>
// is extracted and loaded separately into an Xml object, where it can be manipulated
// independently.  The entire XML file is never entirely loaded into memory.

$fac = new CkFileAccess();

$success = $fac->OpenForRead('qa_data/xml/transactions.xml');
if ($success == false) {
    print $fac->lastErrorText() . "\n";
    exit;
}

$xml = new CkXml();
$sb = new CkStringBuilder();
$firstIteration = true;
$retval = 1;
$numTransactions = 0;

// The begin marker is "XML tag aware".  If the begin marker begins with "<"
// and ends with ">", then it is assumed to be an XML tag and it will also match
// substrings where the ">" can be a whitespace char.
$beginMarker = '<Transaction>';
$endMarker = '</Transaction>';

while ($retval == 1) {
    $sb->Clear();
    // The retval can have the following values:
    // 0: No more fragments exist.
    // 1: Captured the next fragment.  The text from beginMarker to endMarker, including the markers, are returned in sb.
    // -1: Error.
    $retval = $fac->ReadNextFragment($firstIteration,$beginMarker,$endMarker,'utf-8',$sb);
    $firstIteration = false;

    if ($retval == 1) {
        $numTransactions = $numTransactions + 1;
        $success = $xml->LoadSb($sb,true);
        // Your application may now do what it needs with this particular XML fragment...
    }

}

if ($retval < 0) {
    print $fac->lastErrorText() . "\n";
}

print 'numTransactions: ' . $numTransactions . "\n";

?>