Open source OLAP databases are getting increasingly popular in the last few years and have seen mainstream adoption in several big companies such as LinkedIn, Uber, Netflix, Cisco, Bloomberg and so on. Choosing the right OLAP database depends on several factors such as use case, ingestion constraints and methodology, query performance, and production readiness to name a few. In this talk, Neha Pawar and Chinmay Soman (StarTree) present a high-level comparison of 3 such open-source OLAP databases: Apache Pinot, Apache Druid, and Clickhouse with these dimensions in mind. In addition, we will also look at certain salient features in-depth to uncover how things work under the hood across different systems.