How can we speed up database reads for sites with tons of visitors?

we're seeing some slowdowns on our read-heavy endpoints, and i'm wondering how others tackle this. we've indexed common fields, but it's still not cutting it for peak times. are you guys primarily relying on caching layers (like Redis or Memcached), or are there specific database-level optimizations you've found particularly effective beyond basic indexing? curious to hear about your experiences and strategies for keeping read performance snappy under load