$ cat hash.pl
#!/usr/bin/perl

use strict;
use warnings FATAL => 'all';
use Time::HiRes 'time';

my $t0 = time;
my %hash;
$hash{$_} = 1 for 1..3_000_000;
my $t1 = time;
undef %hash;
my $t2 = time;

print "Create:  ", $t1-$t0, "\nDestroy: ", $t2-$t1, "\n";