Twitter is a stream processing precursor. They process ones of the biggest streams in the internet. Storm introduction 5 years ago was a revolution in real-time distributed computing but after few years Twitter decided to replace it. What were Storm issues? Why Heron has been implemented? Why using existing engines was not an option (eg Samza, Spark, Flink) ? Is this a revolution in open source stream processing? I will give you a brief overview of Twitter stream processing history with interesting technical details.