MySQL Index Optimization

Understanding Index Optimization

Index optimization means creating, maintaining, and tuning indexes to maximize query performance while minimizing resource consumption.

Not all indexes improve performance; some can slow down write operations or waste storage.

• Indexes speed up SELECT queries by allowing quick data lookup.
• Too many indexes increase overhead on INSERT, UPDATE, and DELETE operations.
• Unused indexes consume disk space and slow down maintenance tasks.

Identifying Redundant and Unused Indexes

Redundant indexes are those that duplicate the functionality of other indexes.

Unused indexes are those that are never or rarely used by queries.

• Use the MySQL Performance Schema or the sys schema to find index usage statistics.
• Compare index columns to detect overlapping or redundant indexes.
• Remove indexes that do not contribute to query performance.

Best Practices for Index Optimization

Following best practices ensures indexes remain efficient and beneficial.

• Create indexes based on query patterns and WHERE clause columns.
• Avoid indexing columns with low cardinality unless necessary.
• Use composite indexes wisely to cover multiple columns used together.
• Regularly monitor index usage and adjust as application queries evolve.
• Rebuild or optimize indexes periodically to maintain performance.

Maintaining Indexes for Optimal Performance

Index maintenance includes rebuilding, analyzing, and updating statistics.

Fragmented or outdated indexes can degrade query performance.

• Use OPTIMIZE TABLE to defragment tables and indexes.
• Run ANALYZE TABLE to update index statistics for the optimizer.
• Schedule maintenance during low-traffic periods to minimize impact.

Example: Optimizing Indexes for a User Table

Consider a user table with indexes on (user_id), (email), and (user_id, email).

The composite index (user_id, email) covers queries filtering by both columns, making separate indexes potentially redundant.

• Analyze query patterns to confirm index usage.
• Drop redundant single-column indexes if the composite index covers them.
• Monitor performance after changes to ensure improvements.