I always wanted to know memory usage of particular structure in my perl programs. Recently, I noticed that Storable file size corresponds nicely to memory usage of my application, so I used that as a hint of memory usage before loading data.

Then, I decided to show usage of already loaded data. Using Devel::Size total_size seemed like the way to go, but it's much slower than simple Storable piping to /dev/null

             Rate total_size   storable
total_size 4.04/s         --       -70%
storable   13.5/s       234%         --
[download]

using this code

use Benchmark qw(:all);

use Devel::Size;
use Storable;

sub _storable_size {
        open(my $fh, '|-', 'cat > /dev/null');
        Storable::store_fd $_[0], $fh;
        tell($fh);
}

my $o;
$o->{$_} = rand() foreach ( 'a' .. 'z' );
my $hash;
$hash->{$_} = $o foreach ( 0 .. 100_000 );

cmpthese( 100, {
        'total_size' => sub { Devel::Size::total_size( $hash ) },
        'storable'   => sub { _storable_size( $hash ) },
});
[download]

To be honest, I didn't expect so much difference. I can probably setup pipes myself to get a bit more performance, but I would really like to know alternative ways to find out perl memory usage without performance impact.

I'm experimenting with this code in gist on github as a log of things that I tried.

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