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Indexes and Performance Optimization

📚 Lesson 12 of 15 ⏱️ 50 min

Indexes and Performance Optimization

50 min

Indexes improve query performance by providing fast access to data without scanning entire tables. An index is a data structure that allows the database to quickly locate rows matching search conditions. Think of an index like a book's index—instead of reading every page, you can look up a topic and jump directly to relevant pages. Understanding indexes is essential for optimizing database performance. Indexes are especially important for large tables.

Primary keys and unique constraints automatically create indexes, ensuring fast lookups for these important columns. These indexes also enforce uniqueness constraints. Understanding automatic indexes helps you avoid creating redundant indexes. Foreign key columns often benefit from indexes for JOIN performance. Understanding which indexes are created automatically helps you design efficient schemas.

Composite indexes (indexes on multiple columns) can improve queries that filter on multiple columns. The order of columns in a composite index matters—the leftmost columns are most important. A composite index on (A, B, C) can be used for queries filtering on A, (A, B), or (A, B, C), but not for queries filtering only on B or C. Understanding composite index column order enables you to design effective indexes.

The query optimizer chooses the best execution plan based on available indexes and statistics. The optimizer estimates the cost of different execution plans and chooses the most efficient one. Index statistics help the optimizer make good decisions. Understanding how the optimizer works helps you design indexes that will be used effectively. Regular index maintenance (updating statistics, rebuilding indexes) keeps the optimizer informed.

Over-indexing can slow down INSERT, UPDATE, and DELETE operations because each index must be updated when data changes. More indexes mean more maintenance overhead. Finding the right balance—enough indexes for fast queries, but not so many that writes are slow—is key. Understanding the write performance trade-off helps you design appropriate indexing strategies. Monitor index usage to identify unused indexes that can be removed.

Best practices include indexing columns used in WHERE clauses, JOIN conditions, and ORDER BY clauses; using composite indexes for multi-column filters; monitoring index usage to identify unused indexes; maintaining index statistics; and understanding that indexes have storage and maintenance costs. Understanding indexes enables you to optimize database performance effectively.

Key Concepts

  • Indexes provide fast data access without full table scans.
  • Primary keys and unique constraints automatically create indexes.
  • Composite indexes improve multi-column queries.
  • The query optimizer uses indexes to choose execution plans.
  • Over-indexing can slow down write operations.

Learning Objectives

Master

  • Understanding how indexes improve query performance
  • Creating indexes on appropriate columns
  • Designing composite indexes for multi-column queries
  • Understanding the trade-offs of indexing

Develop

  • Performance optimization thinking
  • Understanding database internals
  • Designing efficient database schemas

Tips

  • Index columns used in WHERE clauses, JOIN conditions, and ORDER BY.
  • Use composite indexes for queries filtering on multiple columns.
  • Monitor index usage to identify and remove unused indexes.
  • Understand that indexes have storage and maintenance costs.

Common Pitfalls

  • Over-indexing, slowing down INSERT, UPDATE, DELETE operations.
  • Not indexing columns used in WHERE clauses, causing slow queries.
  • Creating composite indexes in wrong column order, making them ineffective.
  • Not maintaining index statistics, causing poor optimizer decisions.

Summary

  • Indexes provide fast data access without full table scans.
  • Primary keys and unique constraints automatically create indexes.
  • Composite indexes improve multi-column query performance.
  • Understanding indexes enables effective performance optimization.
  • Balance indexing for reads with write performance.

Exercise

Create appropriate indexes for the e-commerce database to optimize common queries.

-- Index for customer lookups by email
CREATE INDEX idx_customers_email ON Customers(Email);

-- Composite index for product searches by category and price
CREATE INDEX idx_products_category_price ON Products(CategoryID, Price);

-- Index for order lookups by customer and date
CREATE INDEX idx_orders_customer_date ON Orders(CustomerID, OrderDate);

-- Index for order items by order
CREATE INDEX idx_orderitems_order ON OrderItems(OrderID);

-- Analyze table statistics for the query optimizer
ANALYZE TABLE Customers, Products, Orders, OrderItems;

Code Editor

Output