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lguidolin/performance-and-scale

Use when working on hot paths, list endpoints, pagination, data-access in loops, or public interfaces/schemas. Symptoms — unbounded queries, N+1 access, no latency budget, optimizing without measuring, or changing an interface many consumers depend on. Keywords — pagination, N+1, Hyrum's Law, performance budget, bundle size.

Qu'est-ce que performance-and-scale ?

performance-and-scale is a Claude Code agent skill that use when working on hot paths, list endpoints, pagination, data-access in loops, or public interfaces/schemas. Symptoms — unbounded queries, N+1 access, no latency budget, optimizing without measuring, or changing an interface many consumers depend on. Keywords — pagination, N+1, Hyrum's Law, performance budget, bundle size.

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npx skills add https://github.com/lguidolin/agent-skills/tree/main/skills/performance-and-scale
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Documentation

Performance and Scale

Overview

Performance is a feature with a budget. Measure it, bound it, and respect that today's behaviors become tomorrow's contracts. Systems rarely fall over at the throughput you designed for — they fall over on the query you didn't index and the list you didn't paginate.

The Principles

  • Set budgets and measure against them. Latency targets (tied to the SLOs of observability-and-slos) and client budgets (e.g. bundle size). A regression past budget is a bug.
  • Measure before optimizing. Find the real bottleneck with data — profiles, query plans, traces — before changing code. No speculative optimization.
  • Paginate by default. Any list that can grow is paginated with a capped page size. Unbounded result sets are a latency and denial-of-service hazard.
  • Beware N+1 access patterns. Data fetched in a loop is the most common scalability failure; batch or join instead. (On this stack: use the GraphQL layer's look-ahead/DataLoader rather than per-row resolution.)
  • Hyrum's Law is real: every observable behavior of an interface becomes a contract someone depends on once it has enough consumers — including behaviors you never intended (ordering, nullability, error shapes, timing). Treat public interfaces (the API/schema especially) as contracts: add and deprecate, don't silently change. The contract tests of graphql-contract-testing pin the behaviors you chose; discipline protects the ones you didn't.

Quick Reference

SmellFix
Query inside a loopBatch or join; use look-ahead
List endpoint with no limitAdd capped pagination
"Let me optimize this" with no measurementProfile first; find the real bottleneck
Changing a field's type/nullability/orderIt's a contract change — add new, deprecate old
No latency or bundle targetSet a budget; treat regressions as bugs

Enforcement: budgets checked in CI where mechanizable (bundle-size limits, query-cost limits); pagination and N+1 avoidance are reviewer judgment backed by load testing and query-plan review.

Full rationale: Article XI of the constitution, bundled at engineering-constitution/references/engineering-constitution.md.

Individual skills in this repo

This repo contains 18 individual skills — each has its own dedicated page.

lguidolin/change-hygiene-and-code-craft

Use when writing or refactoring code, structuring a commit or PR, or deciding whether to abstract duplication. Symptoms — mixing reorg with logic changes, a PR doing several things at once, a file growing large, the second copy of similar code, or unsure whether to DRY something up.

lguidolin/cloud-delivery-aks

Use when deploying to Kubernetes or Azure Kubernetes Service (AKS), configuring cloud secrets, setting up progressive rollout/canary, per-PR ephemeral environments, or k8s health probes. Keywords — Kubernetes, AKS, Key Vault, Argo Rollouts, Flagger, canary, blue-green, liveness, readiness, PodDisruptionBudget, HPA, rollback, GHCR.

lguidolin/commit-history-rewrite

Use when an existing repository has messy commit history that needs to conform to conventional commits before adopting release-please, or when intermediate WIP/fixup/merge commits need to be cleaned up.

lguidolin/conventional-commits-and-releases

Use when committing, writing a commit message, opening a PR that will be squash-merged, or configuring automated versioning/changelogs. Keywords — conventional commits, release-please, semver, feat/fix/chore, breaking change, changelog.

lguidolin/defense-in-depth-security

Use when handling untrusted input, secrets, authentication/authorization, or dependencies — or threat-modeling a new surface. Keywords — STRIDE, threat model, least privilege, secrets management, supply chain, dependency scanning, input validation, audit log, defense in depth.

lguidolin/designing-before-building

Use when starting a feature, fixing a non-trivial bug, or about to write implementation code — before any code exists. Symptoms you need this: "this is simple, I'll just code it", reaching for the editor before a design is approved, or an idea that hasn't been turned into a spec and plan.

lguidolin/engineering-constitution

Use when starting work in a project that follows the engineering constitution, orienting to its rules, or deciding which engineering practice applies to a task — spec writing, commits, testing, security, deploys, database, or UI work.

lguidolin/graphql-contract-testing

Use when writing a GraphQL query/mutation that the UI and a test will share, or building route/schema contract or smoke tests. Symptoms — copying a query into a test, a test asserting on query text, schema change that didn't break the UI build, or RLS/permission drift. Keywords — graphql-codegen, typed document, contract test, route smoke test.

lguidolin/init-repo-CI

Use when setting up a new repository with conventional commits, release-please, and CI automation, or when retrofitting an existing repository that lacks automated versioning and PR validation workflows.

lguidolin/interface-craft-and-accessibility

Use when building or styling UI — components, layouts, forms, design tokens — or making accessibility decisions. Keywords — a11y, WCAG, keyboard navigation, focus state, contrast, design system, minimalist UI, component reuse, ARIA, semantic HTML.

lguidolin/merge-gates-and-automation

Use when setting up or changing CI, pre-push hooks, or a task runner, or deciding what must pass before merge. Symptoms — tempted to put authoritative checks only in a local hook, skip CI, bypass with --no-verify, or unsure what gates a merge vs. runs locally.

lguidolin/observability-and-slos

Use when adding logging, metrics, tracing, health checks, SLOs, or alerting — or when building a service surface that needs to be operable and debuggable. Keywords — structured logs, OpenTelemetry, correlation id, RED metrics, liveness, readiness, SLI, SLO, error budget, alerting.

lguidolin/postgres-postgraphile-rls-and-sql

Use when writing PostgreSQL, PostGraphile config, Row-Level Security policies, SQL schema files, or working on the Browser→App→PostGraphile→Postgres data path. Keywords — RLS, SECURITY DEFINER, search_path, pgSettings, grants, roles, GraphQL depth limit, query cost, statement_timeout, SQL file organization.

lguidolin/recording-decisions

Use when a design or architecture decision has been made and needs to be captured — writing a decision record or ADR, updating a decision index, noting a deferred idea, or superseding a past decision. Keywords — ADR, decision record, rationale, rejected alternatives, dependency index.

lguidolin/resilience-and-deploy-safety

Use when planning a deploy, designing a rollback, or responding to an incident or writing a postmortem. Keywords — deploy safety, rollback, immutable artifact, progressive delivery, canary, blast radius, incident response, blameless postmortem, error budget.

lguidolin/ship-it

Use when the user wants to ship work — push, PR, archive decision records, merge, and clean up. Handles the full lifecycle from committing final changes through post-merge cleanup including converting specs/plans to compact decision records.

lguidolin/tests-as-a-control

Use when writing or modifying tests, when a test breaks during a refactor, or when testing permission/role rules. Symptoms — tempted to edit a test to make it pass, testing only the happy path, a deny-test that started passing, flaky tests, or unsure what to assert.

lguidolin/zero-downtime-migrations

Use when changing a database schema where data must survive the change — adding/removing/renaming columns, constraints, indexes, or backfilling. Symptoms — a destructive migration bundled with a code deploy, a NOT NULL column with a backfill, a table-locking UPDATE, or a rename. Keywords — expand/contract, parallel change, backfill, NOT VALID, CREATE INDEX CONCURRENTLY, graphile-migrate.

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