20K per sort isn't too bad, if your app is not going to run for hours and hours. Even loading a image somewhere will cause a 20k increase.

with Tk::Hlist, you can't bind a sort function to the column, right?

You can, it just isn't obvious from the docs. What you need to do is tell Hlist to use a Button for the header, as in the code below. To bind on the "whole column", there is the x->ev and y->ev methods, but I don't have snippet offhand for that(plus you will be messing with the hlist bindings, unless you use a "right-click" to sort).

#!/usr/bin/perl
use warnings;
use strict;
use Tk;
use Tk::HList;
# googled example by Rob Seegel

my $mw = new MainWindow;
my $hl = $mw->Scrolled(
    'HList',
    -scrollbars => 'os',
    -background => 'white',
    -columns    => 4,
    -header     => 1,
    -width      => 40,
    -height     => 5
)->pack;

my $bgcolor = "bisque";

foreach my $column ( 0 .. 3 ) {

## Create the Clickable Header 
    my $b = $hl->Button(
        -background => $bgcolor,
        -anchor     => 'center',
        -text       => "Header$column",
        -command    => sub {
            print "You pressed Header $column\n";
        }
    );

    $hl->headerCreate(
        $column,
        -itemtype         => 'window',
        -borderwidth      => -2,
        -headerbackground => $bgcolor,
        -widget           => $b
    );

}

MainLoop;
[download]

The first HList example I showed you used itemConfigure. Now MListbox and Listbox don't have itemConfigure, but they are simpler to use. In simple situations, like the first HList sort example, you can get away with $hl->delete('all'), then recreate them all, with no memory gain. However, it is a very simple HList, with just text items. If you get into fancier HList's, say having thumbnail images in the list, Perl's internal reference counting mechanism, will cause HList to leak too, if you do the simpler "delete-rebuild method". In those cases, you have to use itemConfigure to reconfigure each entry with new data. So I generally just stick to itemConfigure all the time.

There are ways to avoid memory gains with Listbox, for instance, the first snippet below will leak, but not the second.

#!/usr/bin/perl -w
use strict;
use Tk;

#this leaks 

my $mw = Tk::MainWindow->new( -title => 'Listbox Leak' );

my $lb = $mw->Listbox()->pack();
my $b  = $mw->Button(
    -text    => 'Leak',
    -command => \&leak
)->pack();

MainLoop;

sub leak {
    $lb->delete( 0, 'end' );
    $lb->insert( 'end', 1 .. 10000 );
}
[download]

#####################################
#!/usr/bin/perl
use warnings;
use strict;
use Tk;

#no leaks, but watch out for @array being empty...crash 
#make sure @array has at least a ''; 
my $mw = Tk::MainWindow->new(-title => 'Listbox Leak');

my @array = (1..10000);

my $lb = $mw->Listbox(
         -listvariable=> \@array,
        )->pack();

my $b = $mw->Button(-text => 'Leak',
        -command => \&leak
          )->pack();

MainLoop;

sub leak {
  @array = map{"$_.a"}(1..10000);
  $lb->update;
}
[download]

Now I havn't messed around much with MList, but any list which allows you do put another object (like a Button) into the list, will leak if you delete entries with a still defined Button in it.