What's the main reason ripgrep is fast?

According to the README, ripgrep is fast for several key reasons [README.md:L183-L210]:

1. Rust's regex engine: It uses finite automata, SIMD, and aggressive literal optimizations to make searching very fast. (PCRE2 support is available via the -P/--pcre2 flag.)

2. Unicode support with performance: Rust's regex library maintains full Unicode support by building UTF-8 decoding directly into its deterministic finite automaton engine, avoiding performance degradation.

3. Smart memory management: It supports searching with either memory maps (better for single files) or incremental searching with intermediate buffers (better for large directories). ripgrep automatically chooses the best strategy.

4. Efficient ignore pattern matching: It applies .gitignore patterns using a RegexSet, allowing a single file path to be matched against multiple glob patterns simultaneously.

5. Parallel directory traversal: It uses a lock-free parallel recursive directory iterator via crossbeam and ignore libraries.

The README notes that while these are the key factors, a single benchmark is never enough—there's a detailed comparison with more benchmarks and analysis available in the blog post on ripgrep.

FOLLOW_UPS:

• How does ripgrep handle binary files by default?
• What are the key differences between ripgrep and GNU grep?
• How can I disable ripgrep's automatic filtering?