I like that Apache Calcite makes query planning and optimization easier without forcing a specific storage system. It is flexible, works with many data sources, and gives developers control to build custom SQL engines while still keeping performance and scalability in mind. Review collected by and hosted on G2.com.

The learning curve can be difficult at first, especially for people new to query optimization or planner rules. Documentation is helpful but sometimes lacks simple examples for advanced use cases, which can make debugging and customization take more time than expected. Review collected by and hosted on G2.com.