Performance Skill

Core Philosophy

"Measure first; optimize where it matters."

Find real bottlenecks with profiling or benchmarks, then improve. Avoid premature or speculative optimization.

Protocol

1. Measure

• Profile: Use language/runtime profilers (e.g. Node: --inspect / Chrome DevTools; Python: cProfile, py-spy; Go: pprof; Rust: cargo flamegraph).
• Benchmark: Add or run benchmarks for the hot path (e.g. benchmark.js, pytest-benchmark, go test -bench, cargo bench).
• Baseline: Record current metrics (time, memory, throughput) so improvements are verifiable.

2. Identify Bottlenecks

• Hot spots: Where the profiler shows most time or allocations.
• N+1 / redundant work: Repeated queries, duplicate computation, unnecessary allocations.
• Algorithm/design: Wrong data structure, O(n²) where O(n) is possible, blocking I/O on hot path.
• I/O: Disk, network, or DB; consider caching, batching, or async.

Focus on the top one or two bottlenecks; avoid scattering small optimizations.

3. Optimize

• Algorithm/data structure: Fix the dominant cost first.
• Caching: Add only where there’s measurable gain and clear invalidation.
• I/O: Batch, pool, async, or reduce round-trips.
• Allocations: Reduce in hot loops (reuse, pool, or avoid unnecessary copies) when the profiler shows pressure.

Preserve correctness and readability; add a short comment or test for non-obvious optimizations.

4. Verify

• Re-run profile or benchmarks; confirm improvement and no regression elsewhere.
• Run the full test suite.

5. Observability & Instrumentation

Add observability to understand production behavior and diagnose performance issues. Use structured logging, metrics (RED method), and tracing for distributed systems.

For complete instrumentation guidance: See reference/INSTRUMENTATION.md, which covers:

• Performance-specific observability (logging, metrics, tracing)
• Instrumentation by ecosystem (Node, Python, Go, Rust)
• Profiling commands by ecosystem
• MCP Integration (Datadog) for performance diagnosis
• Best practices (log slow operations, instrument hot paths, track RED metrics)

Checklist

• Bottleneck identified with data (profile or benchmark), not guess.
• Change targets the hot path or dominant cost.
• Improvement measured; tests still pass.
• Trade-offs (e.g. readability, memory) noted when relevant.
• Observability added: structured logging, key metrics, tracing for distributed calls.
• No sensitive data in logs or metrics; correlation IDs propagated.

Cross-Skill Integration