The queries using Calcite's EnumerableConvention always end-up generating new java classes at runtime (using Janino) that are then instantiated using reflection. This combination of class generation and class loading introduces a big overhead in query response time.
A quick profiling on our Company's internal test suite consisting in 4000 tests with roughly 430000 SQL queries passing through Calcite we observed that a big amount of time is spend on code generation and class loading making the EnumerableInterpretable#toBindable method a performance bottleneck.
Among the 430000 SQL queries there are many duplicates which are going to lead to the generation of exactly the same code Java. Introducing, a small cache at the level of EnumerableInterpretable class could avoid generating and loading the same code over and over again.
A simple implementation based on Guava improved the overall execution time of the afforementioned test suite by more than 50%.