如何提高使用mysql与缓存或其他数据库的应用程序性能

Question

I have api written on Laravel, I use mysql as database, and I have performance issue when getting data from table with 3-4 million rows. Sql functions that i use are: AVG, SUM, COUNT also i use group by and where exists statements in my queries very much. All tables are indexed, so i think that there is few chances to boost the performance by adding or changing table indexes. How can i boost the performance using caches, or is there any DATABASE that can do such calculations on bug amount of data faster than sql.