When we worked on maintenance mode in Database MySQL on Drupal sites, sometime we need to change Our Prefix Tables at new database server, this is a simple trick if you don't want to change one by one table name :)
An appropriate amount of "query_cache" is believed to improve MySQL performance at the expense of available memory. "Appropriate" will vary widely with usage and "performance" on a live site can be elusive. On Ubuntu, the defaults are modest but "work".
I've been working on the performance of my Drupal site and thought I'd share my results to date in case they might help someone else. My baseline performance using out-of-the-box settings was around 28 requests per second, and the end result is a rate of 68 requests per second.