Regex Performance: Avoid Catastrophic Backtracking
Optimize regex performance. Learn catastrophic backtracking, atomic groups, possessive quantifiers, and how to benchmark your patterns.
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Tags: developer-tools, regex, performance
Regex Performance Guide: Avoid Catastrophic Backtracking in Production A regex that works fine on test data can bring down a production server given the wrong input. Catastrophic backtracking — also called ReDoS (Regular Expression Denial of Service) — is a real vulnerability that has caused outages at Cloudflare, Stack Overflow, and others. This guide explains how backtracking works, what makes it catastrophic, and how to write regex that stays fast under adversarial or unexpected input. --- How Regex Backtracking Works Most regex engines use a backtracking algorithm (NFA-based). When the engine tries a path through the pattern and fails, it backs up to the last decision point and tries a different path. Consider the pattern against the string : greedily matches all three s → tries to…
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