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

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Abstract

The database systems course is offered as part of an undergraduate computer science degree program in many major universities. A key learning goal of learners taking such a course is to understand how SQL queries are processed in a 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 commercial RDBMS typically only expose the QEP to users without revealing information about the impact of alternative choices of various physical operators on the QEP 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 a selected QEP for 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. Our demonstration advocates that MOCHA can greatly enhance students’ learning of relational query processing.