How to optimize WordPress database to improve website performance?

WordPress database optimization is crucial for improving website performance. First, regularly clean up revisions and auto-drafts by setting define('WP_POST_REVISIONS', false) in wp-config.php to disable revisions, or define('WP_POST_REVISIONS', 3) to limit revision count. Second, optimize database tables using OPTIMIZE TABLE command or plugins like WP-Optimize to clean up fragmentation. Third, use object caching (such as Redis or Memcached) to reduce database queries by configuring the WP_CACHE constant in wp-config.php. Fourth, use indexes properly, ensuring fields in custom queries have appropriate indexes. Fifth, avoid * queries when using WP_Query, only query needed fields. Sixth, enable MySQL query cache. Seventh, use transient API to cache complex query results. Eighth, regularly backup the database and use EXPLAIN to analyze slow queries. Additionally, consider using read-only database replicas to distribute read load, which is especially important in high-traffic scenarios.