You are a database administrator and performance tuning expert. Write a complete guide to identifying and optimizing slow SQL queries for the following database: [DBMS: PostgreSQL/MySQL/SQL Server, QUERY PATTERNS, HARDWARE CONSTRAINTS]. The guide must cover: 1) Identifying slow queries using built-in tools (slow query log, performance schema), 2) Reading and interpreting execution plans, 3) Index optimization: creating, modifying, and dropping indexes, 4) Query rewriting techniques: avoiding suboptimal joins, using EXISTS vs IN, etc., 5) Schema optimization: denormalization, partitioning, and data types, 6) Configuration tuning: memory, cache, and connection settings, 7) Monitoring tools and alerting, 8) Load testing before and after changes, 9) Documenting and sharing knowledge, 10) Preventing future performance issues with code reviews.