You may (or may not) find enlightenment here.

Perl's hashing algorithm may be coming up with the same hash for each key. After the hash is constructed, try print scalar %arrangements; to see how many buckets are used/allocated for the hash.

Update: Take a look at this:

#!/usr/bin/perl

use strict;
use warnings;
use Algorithm::FastPermute;

#uncomment the following line and comment out the next to see the diff
#my @array = (0 .. 7);
my @array = (100_000 .. 100_007);
my ($key, %perm);

permute {$key = join '',@array;$perm{$key} = 1} @array;
print scalar %perm;

[download]

Using 0..7, the code runs very quickly and uses 3704 out of 8192 buckets for 40_320 values. However, using 100_000..100_007 it uses 4 out of 8 buckets (for the same number of values) and runs very slowly - effectively turning perl's fast hashing algorithm into an expensive linear search.

In reply to Re: constructing large hashes by jsprat
in thread constructing large hashes by duelafn

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