MOCHA: A Tool for Visualizing Impact of Operator Choices in Query Execution Plans for Database Education

The database systems course is offered in many major universities. A key learning goal of learners taking such a course is to understand how sql queries are processed in an rdbms in practice. To this end, comprehension of the impact of various physical operators on the selected query execution plan (qep) of a query is paramount. Unfortunately, off-the-shelf rdbms typically only expose the qep to users without revealing information about the impact of alternative choices of various physical operators on it in a user-friendly manner to aid learning. In this demonstration, we present a novel system called mocha that facilitates exploration and visualization of the impact of alternative physical operator choices on the qep of a given sql query. mocha accepts an sql query as input, and compares and visualizes the qep and alternative plans which are selected based on learner-specified operator preferences. Furthermore, it intuitively explains why the key operators in a qep are chosen by connecting them to established knowledge in the literature.