gstack/review/specialists/performance.md

Performance Specialist Review Checklist

Scope: When SCOPE_BACKEND=true OR SCOPE_FRONTEND=true Output: JSON objects, one finding per line. Schema: {"severity":"CRITICAL|INFORMATIONAL","confidence":N,"path":"file","line":N,"category":"performance","summary":"...","fix":"...","fingerprint":"path:line:performance","specialist":"performance"} Optional: line, fix, fingerprint, evidence, test_stub. If no findings: output NO FINDINGS and nothing else.

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Categories

N+1 Queries

• ActiveRecord/ORM associations traversed in loops without eager loading (.includes, joinedload, include)
• Database queries inside iteration blocks (each, map, forEach) that could be batched
• Nested serializers that trigger lazy-loaded associations
• GraphQL resolvers that query per-field instead of batching (check for DataLoader usage)

Missing Database Indexes

• New WHERE clauses on columns without indexes (check migration files or schema)
• New ORDER BY on non-indexed columns
• Composite queries (WHERE a AND b) without composite indexes
• Foreign key columns added without indexes

Algorithmic Complexity

• O(n^2) or worse patterns: nested loops over collections, Array.find inside Array.map
• Repeated linear searches that could use a hash/map/set lookup
• String concatenation in loops (use join or StringBuilder)
• Sorting or filtering large collections multiple times when once would suffice

Bundle Size Impact (Frontend)

• New production dependencies that are known-heavy (moment.js, lodash full, jquery)
• Barrel imports (import from 'library') instead of deep imports (import from 'library/specific')
• Large static assets (images, fonts) committed without optimization
• Missing code splitting for route-level chunks

Rendering Performance (Frontend)

• Fetch waterfalls: sequential API calls that could be parallel (Promise.all)
• Unnecessary re-renders from unstable references (new objects/arrays in render)
• Missing React.memo, useMemo, or useCallback on expensive computations
• Layout thrashing from reading then writing DOM properties in loops
• Missing loading="lazy" on below-fold images

Missing Pagination

• List endpoints that return unbounded results (no LIMIT, no pagination params)
• Database queries without LIMIT that grow with data volume
• API responses that embed full nested objects instead of IDs with expansion

Blocking in Async Contexts

• Synchronous I/O (file reads, subprocess, HTTP requests) inside async functions
• time.sleep() / Thread.sleep() inside event-loop-based handlers
• CPU-intensive computation blocking the main thread without worker offload