well, you are right, I forgot that mergesort needs additional memory to perform the merge, but yet @a = sort @a uses half the memory required by other sorting expressions, for instance: 
use Memchmark 'cmpthese';

# use sort '_quicksort';

cmpthese( none => sub { my @a = map { int rand 100 } 1..1000000; },
          sort0 => sub { my @a = map { int rand 100 } 1..1000000; @a =
+ sort { $a <=> $b } @a },
          sort1 => sub { my @a = map { int rand 100 } 1..1000000; @a =
+ sort { $a <=> $b } @a, 1 } );

__END__

test: none, memory used: 3997696 bytes
test: sort0, memory used: 7999488 bytes
test: sort1, memory used: 12390400 bytes

[download]
And if the quicksort algorithm is selected, then the sentence on my previous post becomes really true: 
use sort '_quicksort';
...

__END__

test: none, memory used: 3997696 bytes
test: sort0, memory used: 3997696 bytes
test: sort1, memory used: 12390400 bytes

[download]

In reply to Re^3: Howto Avoid Memory Problem in List::MoreUtils by salva
in thread Howto Avoid Memory Problem in List::MoreUtils by Anonymous Monk

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