[benmmurphy]

I think this might also be a case of a phenomena i see frequently especially in chess and searching for vulnerabilities. If someone gives you a chess puzzle and tells you to find the solution its often much easier to do than finding tactics in your own game. i think if you gave a developer who had some understanding of CSS and asked them what the performance problem was they would be able to identify the `matches?` method as the culprit. but if you wrote this code or reviewed this code and you didn't know there was a problem then i think identifying the `matches?` method as a problem would be more difficult. i've been thinking it might even be free to just assume there is a tactic in a chess position or a problem in some piece of code and use that to change your frame of mind to spot these issues. but i don't think this works out in practice because you might be able to change your frame of mind but this comes at a cost of spending more time and focus on the task.

[wutwutwat]

They used their metrics to confirm the regression, and flame graphs to see where the cpu was spending its time. That’s performance tuning basics and anyone who is familiar with profiling code should be able to find the slow spots.

I’ve been doing Ruby for a decade and the matches? method immediately stood out to me. Methods doing any kind of comparison/regex or looping usually end up causing problems. Nokigiri was walking a tree of child nodes and doing a string comparison. I’ve seen people write themselves similar problems with methods like any? includes?, excludes?, etc. Par for the course.