Datamapper memory consumption ? 16Mb exhausted on small query

[eluser]junkwax[/eluser]
No manipulation here, I just want to fetch and display 2000 Id's on a web page.

Code:

$c = new MyClass();
$c->select( 'id' )->limit( 2000 )->get();

foreach( $c->all as $x )
{
  echo $x->id;
}

What's wrong with that code? It eats 16MB of PHP memory.

How should I procede to display the 2000 ids on a page in an optimized way ?