First post here from an eager learner more educated with front end. Please consider the following munin graph:
Considering the general traffic the site on this box got today was the "same" as yesterday, and it was doing the "same" work, why was the CPU utilised in a different way today (as per my understanding of what nice means)
You likely had a background job start around the time the nice % jumps. You can check out the current niceness of processes on the system with ps (i.e. ps -eo cmd,pid,nice, -e for showing all processes, -o for selecting attributes listed in man ps). top will also show you the niceness under the NI column.
Since this is a website it could happen if your web server was restarted with "nice" I've seen it happen in Plesk Panel (Odin). Please verify if the webserver processes are running with nice.
