I'm experiencing a strange Database error in these days, and it could the the cause of the slowness of my website (tasc.it) in these days. I found this error in the PHP error log, I can see about 4-5 times every day, without a logical time distribution.
(I translated the error from italian to english)
WordPress database error Deadlock found when trying to get lock; try restarting transaction for the query DELETE FROM tb_options WHERE option_name = '_transient_doing_cron' executed by require('D:\tasc\wp-blog-header.php'), require_once('D:\tasc\wp-load.php'), require_once('D:\tasc\wp-config.php'), require_once('D:\tasc\wp-settings.php'), do_action('init'), call_user_func_array, wp_cron, spawn_cron, get_transient, delete_option
What does it mean? How can I solve it? I have PHP 5.5, MySql 5.6 both recently upgraded, and Wordpress 3.9.1.