Database performance often comes down to how well your queries are written. A single poorly optimized query can bring an entire application to its knees as data grows.
The EXPLAIN Plan
Before optimizing, you need to understand what's happening. The EXPLAIN (or EXPLAIN ANALYZE) command reveals how the database engine executes your query, showing join strategies, index usage, and estimated costs.
Indexing Strategy
Indexes are the single most impactful optimization tool. Key principles:
- Index columns used in WHERE clauses
- Consider composite indexes for multi-column filters
- Don't over-index — each index has a write cost
- Use covering indexes to avoid table lookups
Common Anti-Patterns
Watch out for SELECT *, functions in WHERE clauses, implicit type conversions, and N+1 query patterns in application code.