...

# Find top 30 customers
# Build a hash for top 30 customers in the
# form of { 'cust1' => balance1, 'cust2' => balance2, ... }
my $top30_customers
   = &GetTopCustomers(\@input_files, $fx_rates, 30);

# Retrieve details about these top 30 customers
my $customer_details
   = &GetCustomerDetails(\@input_files, $top30_customers);

...

sub GetTopCustomers()
{
  my ($inputfiles, $fx_rates, $nth) = @_;
  my %balances;
  ...
  foreach my $file (@{$inputfiles})
  {
    my $f = new IO::File $file, "r";
    ...
    while (<$f>)
    {
       # $cust, $bal, $ccy are extracted from each line
       ...
       $balances{$cust} += $bal * $fx_rates->{$ccy};
       ...
    }
  }
  ...

  # Sort the customers by descending order of balance
  my @sorted_cust_list = 
    reverse map {$_->[0]} sort {$a->[1]<=>$b->[1]}
    map{[$_,$balances{$_}]}keys %balances;

  my %topNth =
    map {$_=>$balances{$_}}(@sorted_cust_list)[0..$nth-1];
    
  # Try to force the garbage collector to work ?@$!%#
  undef %balances;
  undef @sorted_cust_list;

  return \%topNth;
}

##</code><code>##

...

# Find top 30 customers
# Build a hash for top 30 customers in the
# form of { 'cust1' => balance1, 'cust2' => balance2, ... }
my $top30_customers
   = &GetTopCustomers(\@input_files, $fx_rates, 30);

# Try to free up some memory here by starting
# a child process.
my $pid = fork() or die("Can not do fork!);
if ($pid) {
   exit(0); # kill the parent process
}

# Retrieve details about these top 30 customers
my $customer_details
   = &GetCustomerDetails(\@input_files, $top30_customers);

...