In late 2016, Airbnb retired its legacy financial data pipeline. By then, they were transacting in 191 countries, with 70+ currencies and 20+ processors.

The new system decouples the financial logic from the product logic and allows for easier and more reliable horizontal scaling as transaction volume grows. It’s built on Apache Spark and store in an HDFS cluster. It’s written in Scala. They “chose Scala as the language because [they] wanted the latest features of Spark, as well as the other benefits of the language, like types, closures, immutability, lazy evaluation, etc.”