I'm using the following package, which was adapted from http://stackoverflow.com/questions/3790166/, to store a large list of ranges and allow time-efficient "how-many-ranges-cover-this-given-range" queries.

use strict;
use warnings;

package RangeMap;

# Credit: Aristotle Pagaltzis!

sub new($$$) {
    my $class      = shift;
    my $max_length = shift;
    my $ranges_a = shift;
    my @lookup;
    for (@{$ranges_a}) {
        my ( $start, $end ) = @$_;
        my @idx
            = $end >= $start
            ? $start .. $end
            : ( $start .. $max_length, 1 .. $end );
        for my $i (@idx) { $lookup[$i] .= pack 'L', $end }
    }
    bless \@lookup, $class;
}

sub num_ranges_containing($$$) {
    my $self = shift;
    my ( $start, $end ) = @_;
    return 0 unless (defined $self->[$start]);
    return 0 + grep { $end <= $_ } unpack 'L*', $self->[$start];
}

1;
[download]

So, I wonder if I could somehow store it more compactly to save on disk space, without slowing load time too much.

I know it's a give and take - and I'm willing to pay in a longer load (retrieve) time, since my common usage would be a retrieval followed by a few million queries.

Some more details which might be relevant: the number of ranges is usually around 30k, max_length varies significantly between 20k to 15M, where most commonly it's around 3-4M.

Thanks,
Dave