optimize

Performance Optimization Workflow

Profile and optimize a slow Rust operation.

Core constraint: never let a single profiling run exceed 2 minutes.

Steps

1. Baseline profiling run — build in release mode and measure:

   cargo build --release 2>&1
   cargo bench 2>&1 | head -50
   

   If no benchmarks exist, time the target binary directly:

   time cargo run --release -- <args>
   

2. Analyze profile — identify:

   • Which functions dominate cumulative time?
   • Unnecessary allocations or clones?
   • Repeated parsing or serialization?
   • Missing iterator chains (collecting then iterating again)?

3. Identify all optimization opportunities — list everything before implementing:

   • Allocation: reduce clones, use &str over String, reuse buffers
   • Algorithmic: reduce complexity, use appropriate data structures (HashMap vs BTreeMap)
   • I/O: batch operations, use buffered readers/writers
   • Iterator chains: replace collect() + loop with chained iterators
   • Parallelism: use rayon for CPU-bound work where applicable
   • Early exit: short-circuit with find, any, take_while

4. Implement all optimizations in one pass. Follow existing code conventions.

5. Verify tests pass:

   cargo fmt --all
   cargo clippy --tests -- -D warnings
   cargo test
   

6. Measure improvement — re-run profiling, compare to baseline.

7. Iterate — repeat steps 2-6 until no new opportunities are visible.

Rules

• 2-minute cap per profiling run.
• Always profile release builds (--release), never debug builds.
• Batch all optimizations — identify everything, then implement in one pass.
• Tests must pass after every implementation pass — no exceptions.
• Never sacrifice correctness for speed.