Here is what Wikipedia says about Heroku: “Developed in July 2007, Heroku is a cloud Platform-as-a-Service (PaaS) supporting several programming languages and being used as a Web Application Deployment model” … “now supports Java, Node.js, Scala, Clojure, Python, PHP, and Go. Therefore Heroku is said to be a polyglot platform as it lets the developer build, run and scale applications in a similar manner across all the languages – utilizing the dependencies and Profile.”
The Heroku platform is extensible, supporting a wide assortment of third-party data stores, many of which are available directly through the Heroku add-on ecosystem. Even if you require external data store services not provided via the Heroku add-ons library, you can attach them to your apps using configuration variables (config vars). There are several SQL and NoSQL options from the Heroku add-ons library.
There are two primary options for SQL-based databases: Postgres and MySQL. In many modern web application architectures, leveraging a relational, SQL-based database is overkill. Creating a complex schema to represent a relatively simple data model is often not a worthwhile endeavor for most developers. Enter the NoSQL data store. NoSQL stores empower developers to still write their application data to a “store,” much like a traditional database but without the complexity.
Heroku supports MongoDB, Redis, Apache Cassandra and Apache CouchDB.