Performance Tuning (Deep Workflow)

Performance work is measurement-driven. Profile before optimizing; verify after changes; guard against regressions with benchmarks or production metrics.

When to Offer This Workflow

Trigger conditions:

• High CPU, memory, p99 latency, GC pauses
• Cost reduction via efficiency
• Premature optimization requests—need evidence first

Initial offer:

Use six stages: (1) frame goals & SLOs, (2) measure baseline, (3) profile & hypothesize, (4) implement changes, (5) verify & compare, (6) prevent regression). Confirm language/runtime and environment (prod-like data volume).

Stage 1: Frame Goals & SLOs

Goal: Numeric targets: p95 latency, throughput, max memory—not “faster.”

Questions

1. Which workloads matter most (batch vs interactive)?
2. Correctness constraints (approximation allowed or not)?
3. Cost budget for hardware vs engineering time?

Exit condition: One-page success criteria and out-of-scope areas.

Stage 2: Measure Baseline

Goal: Reproducible benchmark or RUM segment—same inputs, same conditions.

Practices

• Warm caches when prod is always warm
• Statistical repeat (multiple runs, discard outliers methodology)

Exit condition: Baseline numbers + environment fingerprint (versions, flags).

Stage 3: Profile & Hypothesize

Goal: Find dominant cost: CPU bound, I/O bound, lock contention, allocation rate.

Tools (examples)

• CPU flame graphs; async wait profiling
• Alloc profiling for GC pressure
• DB query plans and lock waits

Exit condition: Hypothesis tied to evidence (e.g., “40% time in JSON parse”).

Stage 4: Implement Changes

Goal: Smallest change that addresses the hotspot; avoid clever without proof.

Levers

• Algorithm / data structure
• Caching with invalidation discipline
• Batching I/O; connection pooling
• Parallelism where safe—watch locks

Stage 5: Verify & Compare

Goal: A/B or before/after with same workload; watch tail latency not only mean.

Production

• Canary with error rate and latency gates

Stage 6: Prevent Regression

Goal: Micro-benchmarks in CI (optional), budgets, or synthetic checks.

Final Review Checklist

• Goals and baseline documented
• Root cause supported by profiler/trace evidence
• Change scoped; trade-offs explicit
• Verification on realistic load
• Regression guard where feasible

Tips for Effective Guidance

• Little’s Law intuition: queues blow latency—often fix concurrency before micro-opts.
• Avoid optimizing cold paths first.
• GC languages: allocation rate often is the enemy.

Handling Deviations

• Embedded / mobile: battery and thermal constraints matter too.
• Distributed systems: local opt may hurt system (see load-testing).