my $timeout = 10; #10 seconds timeout
foreach my $source (@sources) {
my dbh = connect_to_db($source);
my sth = $dbh->prepare(YOU_QUERY_GOES_HERE);
eval {
    local $SIG{ALRM} = sub {die "alarmn";};
    alarm($timeout);
    $sth->execute(YOUR_PARAMS);
    alarm(0);
};
unless ($@) {
    last;
#ALL OK
} else {
#didnt
    print "Timeout happens!n";
}
}