One thing that was interesting to me:
The outage was caused by a regex that ended up doing a lot of backtracking, which caused PCRE, the regex engine, to essentially handle a runaway expression.
This reminded me of a HN post from a couple months back by the author of Google Code Search, and how it worked: https://swtch.com/~rsc/regexp/regexp4.html . Interestingly, he wrote his own regex engine, RE2, specifically because PCRE and others did not use real automata and he needed a way to do arbitrary regex search safely.
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