use POSIX ":signal_h";
my $mask = POSIX::SigSet->new( SIGALRM );
my $dbh = ...;
my ($t) = $dbh->selectrow_array("SELECT CONNECTION_ID()");

my $sth = $dbh->prepare("mein select");
my $action = POSIX::SigAction->new(      
    sub {
        my $dbh = ...;
        my $foo = $dbh->prepare("kill ?");
        $foo->execute($t);
        die "connection ($t) timeout";
    }, 
    $mask,
);     
my $oldaction = POSIX::SigAction->new(); 
sigaction( SIGALRM, $action, $oldaction ); 
eval {
    alarm 5;
    $sth->execute(...);
    alarm 0;
};  
alarm 0;
sigaction( SIGALRM, $oldaction );
if ($@) {
    ...
}