magentoCollectionIteration.php

<?php

$collection = Mage::getModel('catalog/product')
    ->getCollection()
    ->addAttributeToFilter('col', array('eq' => $value));

// Add a page size to the result set.
$collection->setPageSize(25);
$pages = $collection->getLastPageNumber();
$currentPage = 1;

do {
    // Tell the collection which page to load.
    $collection->setCurPage($currentPage);
    $collection->load();

    foreach ($collection as $item) {
        // do stuff

        // tip to save memory
        // $_child = Mage::getModel('catalog/product')->load($child->getId());
        // $_child->clearInstance();
    }


    // make the collection unload the data in memory so it will pick up the next page when load() is called.
    $collection->clear();
    $currentPage++;

} while ($currentPage <= $pages);