Hey there,
there is a (unnecessary) huge mysql request in your Calendar that chrashed our database several times in the past days.
We run a blog with about 80.000 posts and 50.000 media elements (pictures, etc.). Obviously, your Calendar (the widget maybe?) goes through each and every database entry (posts, pictures, users, tags, …) and sorts them before showing the top 5 (and deleting everything else afterwards). In our case, this causes the server to download the whole database to hd to perform this task, since the db is way too big to be processed in the memory. There is a query called databasename_posts.* which causes the main problem.
Unfortunately, we are not able to use this plugin anymore, until there is a fix for this issue.