you should tweak the PHP codes such that no too PHP process should run for long time or force them to disconnect as soon as they don't need to access the database anymore. As per my observation, many PHP processes was taking high load which was almost near to 99-100%. It could have been because of the more sleep queries. As per my previous experience with other MySQL servers, in servers where there are high sleep queries, the SQL server will get unstable. Hence feel free to tweak the PHP file which makes connection with MySQL/databases."