#!/usr/bin/perl

use strict;
use warnings;

use Time::HiRes qw( time );

my $qfn = 'file';

{
   open(my $fh_out, '>', $qfn)
      or die;
   binmode($fh_out);

   for (1..1_000_000) {
      # Limit the ID in order to get collisions.
      print $fh_out (pack('I', rand(65536)));
      print $fh_out (join '', map chr(rand(255)), 1..4);
   }
}

my $stime = time;

{
   open(my $fh_in, '<', $qfn)
      or die;
   binmode($fh_in);

   my %hash = ();
   while (read($fh_in, my $packed_data = '', 8)) {
      my ($id, $val) = unpack 'II', $packed_data;
      push @{$hash{$id}}, $val;
   }
}

my $etime = time;
print($etime-$stime, "\n");

unlink($qfn) or warn;