This has to do with an ODBC default length. Check the data here. This will suggest something like the following be used :

# ...
$dbh->{LongReadLen} = 20000;
$sth = $dbh->prepare("select long_col from big_table"); $sth->execute;
# ...
[download]

---

Thus spake the Master Programmer:
"When you have learned to snatch the error code from the trap frame, it will be time for you to leave."
-- The Tao of Programming