For more than 4 hours i've been checking into this issue and monitoring the server. All softwares and processes seems runs as they should be, there's no significant inrease in term of traffic/users but the load of the database server is higher than usual. What causing it is still a mistery to me.
I contacted one of the tech-support from the company that suppose to [i]manage[/i] my servers, but he didn't do anything and I only got unsatisfactory answers for my questions about this problem.
I also tried to reinstall some softwares, modified the php configurations, and just a while ago I put the forum into maintenance mode to rebuild the search index in the database, but I still don't see any difference in speed/performance.
Maybe later I'll ask the server provider to check if there's any problem with the hardware (While performing the hardware check friendstertalk will be unaccessible).