MongoDB - Why should I use a cursor instead of iterator_to_array (in PHP)

Question

The PHP documentation for the mongo class says using a cursor instead of iterator_to_array is superior.

Why? What benefits/flexibility will I get from that?

Answer 1

Using iterator_to_array() makes your driver load all of the results into memory at once, and you could easily run out of memory. This would not be the case with a cursor, which uses lazy-loading!

Straight from the linked docs:

<?php

$cursor = $collection->find();
var_dump(iterator_to_array($cursor));

?>

...

Suppose that, in the example above, $collection was a 50GB collection. We certainly wouldn't want to load that into memory all at once, which is what a cursor is for: allowing the client to access the collection in dribs and drabs.