I am at all ends with this problem and really hope someone here can help;
my site http://www.eurocfo.com is having some very tempermental outages.
firstly let me confirm a few basics;
1. The wp-config.php file is exactly as it was two years ago and no database changes have been made.
2. Our host have confirmed and assured me that their database server is running without any issues.
3. I use in addition 3 plugins to make the site work, I have disabled these plugins to ensure we don't have a conflict ion.
4. WordPress is up-to-date and running the latest version.
Our host emailed this to us, but If I'm honest, I don't know where to look or what to look for;
It appears that the connections are being maxed out to the database which is being shown by the intermittent error message we are getting.
I would therefore recommend you view the scripts and check to ensure that sessions / connections to the database are terminated instantly to free the connections.
I noticed that as soon as we restart the application the error disappears due to all the connections being dropped, however shortly lived it comes back when the connection limits are hit which is currently set to 20.
I appreciate all your help on this matter