Another update, just in case someone searching for CGI::Session needs to know this.

If you wish to use mysql to store the session data _and_ use a tablename other than 'sessions', then you must explicitly call

use CGI::Session;
use CGI::Session::MySQL;
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before setting

$CGI::Session::MySQL::TABLE_NAME = 'alt_name';
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It's not enough to just use CGI::Session; as the docs state.

(if you don't, then creating the new CGI::Session object will load the CGI::Session::MySQL module for you, which overwrites the value you set.)