about codeigniter3 session

Then use the session database.

too many records,
I have no time to delete and manage

PHP should automatically cleanup old sessions (regardless of which driver you use) based on the settings session.gc_probability, session.gc_divisor, and session.gc_maxlifetime, usually set in php.ini (but it can be set elsewhere, if needed).

Some Linux installations (especially Debian-based distributions like Ubuntu) set these variables so the built-in garbage collector won't run, then add their own cron job to do it every 30 minutes or so. The only problem with that is that you probably aren't using the default location for session data, so you would have to either change the settings or create your own cron job to perform the garbage collection.

Bonfire

Practical CodeIgniter 3
CodeIgniter Testing Guide