Performance schema
https://dev.mysql.com/doc/refman/5.5/en/performance-schema.html
https://mariadb.com/kb/en/mariadb/performance-schema-overview/
https://dba.stackexchange.com/questions/27328/how-large-should-be-mysql-innodb-buffer-pool-size#27341
https://serverfault.com/questions/363355
master slave & sharding
https://mariadb.com/products/technology/maxscale
https://www.percona.com/blog/2016/08/30/mysql-sharding-with-proxysql/