As you describe it, the (memory) bottle neck is when you start processing the array. Shifting off the elements at each iteration will save memory - but the memory isn't released back to the OS - it just means that it takes longer before Perl needs to ask more memory from the OS. So, wether it helps to speed up the program depends on what else you do in the program - if you won't use much more memory, there's little gain. OTOH, shift is a fast operation, so there's not much reason to not do it.

If however you are looking for a real performance boost, look into an algorithm that doesn't require the entire array to exist at one time. The fact you don't need an element anymore after you process it suggests you may not need all the elements before processing the first one either.

Abigail