Stack Overflow Outage Postmortem
> So the Regex engine has to perform a “character belongs to a certain character class” check (plus some additional things) 20,000+19,999+19,998+…+3+2+1 = 199,990,000 times, and that takes a while.<p>199,990,000 isn't really <i>all</i> that many. I'm a little surprised it didn't just cause a momentary blip in performance.<p>edit: whoops, i guess that's per page load