PHP XML memory leak?

Question

We have a serious memory leak in one of our regular scripts that quickly destroy free memory on the server. Despite many hours of research and experimentation, I could not even go into it.

Here is the code:

    echo '1:'.memory_get_usage()."\n";
ini_set('memory_limit', '1G');
    echo '2:'.memory_get_usage()."\n";

$oXML = new DOMDocument();
    echo '3:'.memory_get_usage()."\n";
$oXML->load('feed.xml'); # 556 MB file
    echo '4:'.memory_get_usage()."\n";

$xpath = new DOMXPath($oXML);
    echo '5:'.memory_get_usage()."\n";
$oNodes = $xpath->query('//feed/item'); # 270,401 items
    echo '6:'.memory_get_usage()."\n";

unset($xpath);
    echo '7:'.memory_get_usage()."\n";
unset($oNodes);
    echo '8:'.memory_get_usage()."\n";
unset($oXML);
    echo '9:'.memory_get_usage()."\n";

And here is the conclusion:

1:679016
2:679320
3:680128
4:680568
5:681304
6:150852408
7:150851840
8:34169968
9:34169448

As you can see, when we use xpath to load nodes into an object, memory usage jumps from 681 304 to 150 852 408. I am not very worried about this.

My problem is that even after the destruction of the $ oNodes object, we are still stuck using memory 34,169,968.

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Answer 1

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Answer 2

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// ps reports X memory usage
var $foo = (new DomDocument())->loadXML(getSomeXML());
// ps reports X + Y memory usage
var $foo = (new DomDocument())->loadXML(getSomeXML());
// ps reports X + ~2Y memory usage
var $foo = (new DomDocument())->loadXML(getSomeXML());
// ps reports X + ~3Y memory usage

unset() ...

// ps reports X memory usage
var $foo = (new DomDocument())->loadXML(getSomeXML());
// ps reports X + Y memory usage
unset($foo);
var $foo = (new DomDocument())->loadXML(getSomeXML());
// ps reports X + ~Y memory usage
unset($foo);
var $foo = (new DomDocument())->loadXML(getSomeXML());
// ps reports X + ~Y memory usage

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