What's the main reason ripgrep is fast?

According to the README, ripgrep is fast for several interconnected reasons:

1. Rust's regex engine: ripgrep is built on top of Rust's regex engine, which uses finite automata, SIMD, and aggressive literal optimizations to make searching very fast [README.md:L188-L190].

2. Unicode support without performance loss: Rust's regex library maintains performance while supporting full Unicode by building UTF-8 decoding directly into its deterministic finite automaton engine [README.md:L191-L193].

3. Intelligent search strategy selection: ripgrep supports searching with either memory maps (better for single files) or incrementally with an intermediate buffer (better for large directories), and automatically chooses the best strategy for you [README.md:L194-L196].

4. Efficient ignore pattern matching: It applies your .gitignore patterns using a RegexSet, which allows a single file path to be matched against multiple glob patterns simultaneously [README.md:L197-L199].

5. Parallel directory traversal: ripgrep uses a lock-free parallel recursive directory iterator via crossbeam and ignore libraries [README.md:L200-L202].

The combination of these factors—particularly the underlying regex engine's use of finite automata and SIMD optimizations—forms the foundation of ripgrep's speed advantage.

FOLLOW_UPS:

• How does ripgrep's regex engine compare to PCRE2?
• What automatic filtering does ripgrep perform by default?
• How does the memory map strategy work compared to buffering?