Further to davido's discussion of the Perl interpreter's efforts to manage memory for your arrays (and hashes and everything else):
geertvc: Note that if you have an array that starts small and that will grow to a very large size that you know (or can estimate) in advance, it's possible and occasionally advantageous to "pre-grow" the array by assignment to the array's max index via the  $# array dereference operator (if that's the correct terminology).

c:\@Work\Perl\monks>perl -wMstrict -le
"my @ra = qw(a b c);
 print 'A: array max index: ', $#ra;
 ;;
 $#ra += 1_000_000;
 print 'B: array maximum index:      ', $#ra;
 print 'B: number of array elements: ', scalar @ra;
"
A: array max index: 2
B: array maximum index:      1000002
B: number of array elements: 1000003
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See perldata regarding $#. In most cases, however, it's best to let the interpreter manage these things on its own.