php - Multiple foreach loop and just another memory leak story

To whom may concern,

As we are already known foreach is a painful and a headache while we using it to deal with thoudsands or millions of record. And it will become a bloody killer machine if we have a twin or may be more foreach in a row :)

For example,

foreach ($parent as $parentData) {
    // few conditional added here
    $parentObj = $this->extract();
    foreach ($chilren as $childrenData) {
        if ($childrenData['id'] === $parentData['id']) {

            $childrenObj = $this->extract();
            $parentObj->setData($childrenObj);
            // and even more evil things come here....
        }
    }
    $parentObj->save();
}

In my situation, I have twin foreach. And each one contains approximate 50,000 ~ 70,000 records. $parent and $children are parameters passed to the method.

The raw data source both of $parent and $children are CSV files. And I'm using yield to transform them to be travelsable with foreach.

There is no trouble with yield, belive me. It's guaranteed by a 60k+ player of this site :)

If you concern about the code: https://stackoverflow.com/a/37342184/2932590

Back to my concernation, I tried to unset both of $parentObj and $childrenObj at the end of first foreach, but unfortunately it's not working. I also tried to using the references &$parentData, but the result is same.

How could I make this work till the rest of my life?

Thanks in Advanced.

I got few advised to use SPL Iterators in this case. Can anyone please explain me how it work also?

Thanks.

I'm using SPL Iterator, below is the new code:

$parent = new IteratorIterator(new ArrayIterator($parentArr));
$children = new IteratorIterator(new ArrayIterator($chilrenArr));
foreach ($parent as $index => $parentData) {
    $parentObj = null;
    // few conditional added here
    $parentObj = $this->extract();
    $childrenObj = null;

    foreach ($chilren as $key => $childrenData) {
        if ($childrenData['id'] === $parentData['id']) {
            $childrenObj = $this->extract();
            $parentObj->setData($childrenObj);
            // and even more evil things come here....
        }
    }
    $parentObj->save();
    $childrenObj->save();
}