use strict;
use warnings;
use KyotoCabinet;

# construct the database object
my $db = KyotoCabinet::DB->new();

# open the database
if (! $db->open('input_a.kct#pccap=256m', $db->OREADER)) {
    die "open error (db): ", $db->error;
}

# open input_file b
open my $fh_b, '<', 'input_b.txt' or die "open error (txt): $!";

my $key_b = '';
my @val_b = '';

sub output_key {
    # process key
    foreach my $val_a ( split(' ', $db->get($key_b)) ) {
        foreach my $val_b ( @val_b ) {
            print "$key_b $val_a $val_b\n";
        }
    }
}

while ( my $line = <$fh_b> ) {
    chomp $line;
    my ($key, $val) = split(' ', $line, 2);
    if ($key ne $key_b) {
        output_key() if $key_b;
        $key_b = $key;
        @val_b = ();
    }
    push @val_b, $val;
}

output_key() if $key_b;

close $fh_b;
$db->close;