It might be time to rethink that business decision. Anyway you can save some memory if you think about what you are doing.

# get the customer => blance hash mapping - if you can't RDBMS you are
+ stuck with this
$cust_bal = ......
# now all we are interested in is the top 30
# we don't need to sort them all using a Schwartzian
# we only need to sort the values. This saves us a lot of memory as 
# [ cust, bal ] will take up a lot more space than just bal
# we can also exit at this point and write a new temp flat file
# with all the cust => bal mappings and this reclaims the memory.
# either way we just want those top 30 so just sort the balances:
my @bals = sort { $b <=> $a } values %$cust_bal
# we are only interested in the top 30 which is a balance greater than
+....
my $gt = $bal[30]
# so now we iterate over our hash again (or the flat file)
my $top_30;
for my $cust( keys %$cust_bal ) {
  next unless $cust_bal > $gt;
    $top_30->{$cust} = $cust_bal->{$cust};
}
# now the top_30 are in a hash ready to be sorted for mapping to cust 
+details and output
[download]

This will save you roughly 25% and up to 50% (by using a temp file) of the memory that the original algorithm used which might get you home. If not you will have to tie your hash to a file. dbmopen might be the DB you have when you are not having a DB :-) If you can't do it in memory and have to tie to the disk it will be really slow, but I gues you have got all day :-)

cheers

tachyon

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