HOW LINKEDIN SERVES 5 MILLION USER PROFILES PER SECOND

Summary from the TLDR Web Dev newsletter

LinkedIn's user profile views created a massive read workload that pushed the limits of its existing document database, Espresso. To solve this, its team introduced Couchbase, a distributed NoSQL database, as a caching layer to reduce the read load on Espresso. They designed the caching layer to be independent of Espresso to avoid cascading failures if Couchbase experienced issues. The entire profile dataset is cached in every data center for quick access.