it's a nice feature not a must have feature trace what mariadb is doing in optimizer, some time (in bugs or performace problem) is nice to see what is going wrong, and why a must have feature, for me, is lock partition prune i have many myisam table with lock problem and partition lock prune can solve it, today i changed the some codes to use union, but i will change it to only use partitions when partition lock is enabled the memcache is a nice feature too since i can remove nosql servers (memcached) from processlist and use more memory in mariadb server maybe a benchmark (if possible) about handler socket and memcached could be nice, i think today we can only do this in mysql server, but it's a nice information, sometimes is easier to change programs to use handler protocol instead of using memcached protocol, but it must give near performace with time i can do this benchmark, but not now, i will mark it in my todo list