MySQL tuning (my.cnf) for very large tables and ad hoc queries
very large tables more then 70Million to query


If you have more than 70 million tables then you need to get a big stick and apply it repeatedly to the person responsible for this. 

There's lots of things you do to improve the performance a database (and ignoring this line, some small changes could massively increase the performance of a sensible schema) - but until you sort the number of tables you are wasting your time.