What's the main reason ripgrep is fast?

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

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. (PCRE2 support can be opted into with the -P/--pcre2 flag.)

2. Unicode support without performance loss: Rust's regex library maintains performance with full Unicode support by building UTF-8 decoding directly into its deterministic finite automaton engine.

3. Smart search strategy selection: It supports searching with either memory maps (better for single files) or incrementally with an intermediate buffer (better for large directories). ripgrep automatically chooses the best strategy for you.

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

5. Parallel directory iteration: It uses a lock-free parallel recursive directory iterator via the crossbeam and ignore crates.

The fundamental performance advantage comes from the underlying Rust regex engine's use of finite automata and SIMD optimizations, combined with intelligent choices about how to apply those searches across files and directories.

FOLLOW_UPS:

• How does ripgrep's performance compare to other search tools?
• What is the difference between memory map and buffer search strategies?
• How does the ignore crate handle .gitignore pattern matching?