When session writes

When and where the session writes in CakePHP 2.x. In my webpage there is 2 types of login Admin and user. I made the session setting as write in the database.

Configure::write('Session', array(
    'defaults' => 'database',
    'handler' => array(
        'model' => 'cake_sessions'

When I logged in and logged out as a user and logged in as a Admin, Session not stored in the database. But When I logged out as Admin, It stores data in the database

    "id" : "14f3190cee9b45fbef6d825f06845634",
    "data" : "Config|a:3:{s:9:"userAgent";s:0:"";s:4:"time";i:1487143496;s:9:"countdown";i:10;}Message|a:1:{s:5:"flash";a:3:{s:7:"message";s:20:"You have logged out.";s:7:"element";s:7:"default";s:6:"params";a:0:{}}}jdebug_output_carry_over|a:4:{s:11:"development";b:1;s:9:"geo_cache";s:4:"miss";s:4:"city";s:7:"unknown";s:6:"region";s:7:"unknown";}"
    "expires" : "1487143496"

So Can you please guide me, how it works?