Rationale

“Online“ means that the final result is constantly updated as new tuples arrive in the system. At each step, the system represents an eventually correct query result for the tuples seen so far.

Squall translates a SQL query into a query plan consisting of a DAG of Relational Algebra operators. Each operator is implemented as a Storm component (Spout or Bolt), so that the query plan is executed as a Storm topology. Currently, we have implemented a heuristic-based optimizer which generates bushy plans.