Hi Ernest,
I really appreciate the effort you put in your response. God knows, it’s rare to have good support.
I think I have found what may cause a part of the overhead. I enabled statistics and in a few hours I gathered a lot of “No keyword” searches. I wonder what may cause that? Is it because it’s the first thing on my page and it might autofocus on some browser?
Also, concerning the “SHOW TABLE” thing. The problem is that, as a query it is not cachable and mysql does write a temp table to disk to produce the result. It would be much more efficient to set a flag with update_option once you found it and then use get_option to check if it has been created since those query will get cached either by a WordPress Caching Plugin, Redis/Varnish or MySQL.
Anyway, I’m still happy.
Have a nice day.