Regex Performance
Bad regex can cause catastrophic backtracking, freezing your application. Here's how to avoid it.
1. Be Specific
Bad: .* (matches everything)
Good: [^\n]* (matches everything on one line)
2. Avoid Nested Quantifiers
Bad: (a+)+ can cause exponential backtracking
Good: a+ (same result, no backtracking)
3. Use Non-Capturing Groups
Use (?:pattern) instead of (pattern) when you don't need the captured value. It's faster.
4. Anchor Your Patterns
Add ^ and $ to avoid scanning the entire string unnecessarily.
5. Use Possessive Quantifiers
a++ (possessive) prevents backtracking. Not supported in all engines but great when available.
Catastrophic Backtracking Example
^(a+)+$ with input "aaaaaaaaaaaaaaaaaaab" can take minutes to fail.
Fix: ^a+$ — same logic, no exponential backtracking.