use GDBM_File;
use MLDBM qw(GDBM_File Storable);
use Thing;                         ## (Thing is a package)

tie (my %hash_db, "MLDBM", 'output.db', &GDBM_WRCREAT, 0606);
foreach my $key (keys %hash_db) {
    my $current_thing = $hash_db{$key};
                        ## do something with current_thing
    $hash_db{$key} = $current_thing;
}
untie %hash_db;