What is the space complexity of quicksort?
Since worst case space complexity of $\Theta(n)$ could be a problem, you can make a slight modification to the Qicksort algorithm: Partition the array, then sort the smaller half recursively, and sort the larger half iteratively. Roughly:
Sort (range r)
    While r contains two or more elements
        Partition range r
        Sort (smaller sub partition)
        r = larger sub partition 

This reduces the worst case space required to $\Theta(\log n))$. It does not help with the worst case execution time.