why MySLQ datadir must be owned by mysql user? I read this from MySQL document:


  Otherwise, most of the MySQL installation can be owned by root if you like. The exception is that the data directory must be owned by mysql.



Can somebody tell me why? 
Why data directory owned by root is not good?
When MySQL is running, it runs as the mysql user account. If the data directory was owned by root, MySQL would not have permission to write to it!