ci_sessions table is getting big - like 6M records and 90meg big

ci_sessions table is getting big - like 6M records and 90meg big

Is there any problem with me just truncating the table?

These are my settings in config

PHP Code:

$config['sess_driver'] = 'database';
$config['sess_cookie_name'] = 'ci_session';
$config['sess_expiration'] = 7200;
$config['sess_save_path'] = 'ci_sessions';
$config['sess_match_ip'] = FALSE;
$config['sess_time_to_update'] = 300;
$config['sess_regenerate_destroy'] = FALSE; 


I also note that my table did not have the primary key set:

PHP Code:

// When sess_match_ip = FALSE
ALTER TABLE ci_sessions ADD PRIMARY KEY (id); 


So my plan is to truncate the table (knock it to 0 records) and then add the primary key.

Buuuuut - this is a production DB so I want to get the advice of the learned folks here before I commit such an act.

Also why would my sessions in ci_sessions not be being cleaned up by the garbage collector?