Quoted:Quoted:
One-time event (shrug) or periodic?
This is it. You see that perfect slow escalation?
I do; it's ringing no bells. By periodic I meant (should have been clearer) was it an event that occurred once yesterday, never seen before or since –– which is clearly what I think you're saying. It's interesting enough that if it was periodically recurring, you could meter the hell out of the system.
Sorry, not a Mac guy at all. So the normal tools I'd suggest for a real-time analysis (top to figure out which process(es) looked strange; strace -f -p $PID -o $OUTPUT_FILE to attach and try to snag a clue [or truss or dtrace or ...) may not help.
NimmerMehr's suggestion about a bad regex is interesting; on the other hand, I would expect a much steeper curve for that sort of cause. I have also seen VMs and their launched applications slowly chew up CPU and/or memory.