> 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.
199,990,000 isn't really all that many. I'm a little surprised it didn't just cause a momentary blip in performance.
SO is I/O bound most of the time. If you've set up your system to handle high workloads of I/O bound traffic, then hitting CPU bounds throws a real wrench in your cogs.
To put this another way, SO is one of the most traffic'd sites on the internet. So a page that's loaded 10k+ times a second is going to push that number much, much, higher. If the CPU can't clear 10k+ req in under the regular time it takes, everything starts to back up.
Alexa puts it at rank 50 globally. Honestly this seems suspiciously high and I wonder if their sampling method is biased. Regardless, it's a lot of traffic.
They mentioned that the drop in performance caused the load balancer to remove the servers from rotation. They said that the site would have otherwise been pretty functional. So the resolution to the issue (aside from fixing the regex) was to update the configuration of the loadbalancer/healthcheck to avoid this type of issue.
I presume the strip function happens on every request for the page, which as the homepage for stackoverflow, means 199,990,000 times quite a lot of requests a second.
199,990,000 isn't really all that many. I'm a little surprised it didn't just cause a momentary blip in performance.
edit: whoops, i guess that's per page load