MySQL performance issues manifest as slow queries, high CPU, or memory pressure. Systematic optimization addresses queries first, then indexes, then server configuration. Most gains come from query and index improvements.
Query Optimization
Use EXPLAIN to understand query execution plans. Identify full table scans requiring indexes. Optimize JOINs ensuring indexes support join conditions. Limit result sets early in query execution.
- Run EXPLAIN ANALYZE for actual execution statistics
- Ensure JOIN columns are indexed appropriately
- Avoid SELECT * fetching unnecessary columns
- Use LIMIT for pagination preventing large result sets
- Consider query caching for repeated identical queries
Index Strategy
Create indexes supporting WHERE, JOIN, and ORDER BY clauses. Composite indexes serve multiple columns efficiently. Cover indexes include all query columns avoiding table lookups. Monitor unused indexes for removal.