use MCE::Loop;
use DBI;

sub db_iter {
   my $dsn = "DBI:Oracle:host=db_server;port=db_port;sid=db_name";

   my $dbh = DBI->connect($dsn, 'db_user', 'db_passwd') ||
             die "Could not connect to database: $DBI::errstr";

   my $sth = $dbh->prepare('select color, desc from table');
   $sth->execute();

   return sub {
      my $chunk_size = shift;

      if (my $aref = $sth->fetchall_arrayref(undef, $chunk_size)) {
         return @{ $aref };
      }

      return;
   }
}

## Let's enumerate column indexes for easy column retrieval.
my ($i_color, $i_desc) = (0 .. 1);

MCE::Loop::init {
   max_workers => 3, chunk_size => 1000,
   input_data => db_iter(),
};

mce_loop {
   my ($mce, $chunk_ref, $chunk_id) = @_;
   my $ret = '';

   foreach my $row (@{ $chunk_ref }) {
      $ret .= $row->[$i_color] .": ". $row->[$i_desc] ."\n";
   }

   MCE->print($ret);
};

MCE::Loop::finish;