I have set up memcached, confirmed in PHPinfo within the moodle site, for a particular 2.8.2 Moodle site. I can see memcached is working on the server. I checked the Session handling page and it looks a bit different from the 2.6.* version when I enabled it before.
Anyway, even though memcached works, and I believe the site is connecting to memcached for sessions, it still throws these lock queries to the database. It floods the database with these DB locks to the moodle sessions table.
This seems different from 2.6.* when memcached is enabled, you wouldn't see any activity in the sessions table in the DB. But now in 2.8.2 I see all this activity. The problems come when I get thousands of these happening all at once and the database comes to a halt as a result of all the table locks.