# 06. Database Connection Pooling & Query Optimization

meta:
  id: web-production-06
  feature: web-production
  priority: P1
  depends_on: []
  tags: [performance, database, production]

objective:
- Optimize database connections and queries for production load

deliverables:
- Connection pooling configuration
- Query performance audit
- Index optimization
- Slow query logging

steps:
1. Configure connection pooling:
   - If using PostgreSQL: configure PgBouncer or use @libsql/client pooling
   - Set max connections based on server instances (e.g., 20 per instance)
   - Add connection timeout and idle timeout settings
2. Audit all Drizzle queries for performance:
   - Check web/src/server/db/schema/*.ts for missing indexes
   - Review web/src/server/api/routers/*.ts for N+1 queries
   - Add pagination to all list endpoints (default 50, max 100)
3. Add database indexes:
   - createdAt indexes for time-range queries (alerts, exposures)
   - Composite indexes for common filter combinations
   - userId indexes on all user-scoped tables
4. Implement query result caching:
   - Cache user profile lookups (5 min TTL)
   - Cache subscription status (1 min TTL)
   - Cache dashboard summary (30 sec TTL)
5. Add slow query logging:
   - Log queries taking >500ms
   - Alert on >1s queries
6. Set up database performance monitoring

tests:
- Unit: Test query execution plans for major endpoints
- Load: Run 1000 concurrent dashboard loads, verify <200ms p95
- Integration: Test pagination boundaries

acceptance_criteria:
- Database connection pool configured with max 20 connections
- No N+1 queries in any API endpoint
- All list endpoints paginated with cursor or offset
- Slow query logging active
- Dashboard load query <100ms p95
- Alert endpoint query <50ms p95

validation:
- EXPLAIN ANALYZE on major queries shows index usage
- Load test with k6: 1000 concurrent users, p95 < 200ms
- Database CPU <50% under normal load

notes:
- Current schema has some indexes but may need more for production scale
- Drizzle ORM doesn't automatically handle connection pooling — configure at driver level
- Consider read replicas if dashboard load is heavy