What methods have you used to improve the performance and scalability of relational databases in your projects?

To improve the performance and scalability of relational databases, I applied the following methods:

• Indexing frequently used columns to speed up queries.
• Optimizing SQL queries by avoiding redundant JOINs and subqueries.
• Using caching at the application or database level.
• Vertical scaling (increasing server resources) and horizontal scaling (replication, sharding).
• Partitioning tables to enhance handling large volumes of data.

For example, in one project, adding indexes on columns involved in filters reduced query execution time from several seconds to milliseconds.