SIA: Optimizing Queries using Learned Predicates

Predicate-centric rules for rewriting queries is a key technique in optimizing queries. These include pushing down the predicate below the join and aggregation operators, or optimizing the order of evaluating predicates. However, many of these rules are only applicable when the predicate uses a certain set of columns. For example, to move the predicate below the join operator, the predicate must only use columns from one of the joined tables. By generating a predicate that satisfies these column constraints and preserves the semantics of the original query, the optimizer may leverage additional predicate-centric rules that were not applicable before. Researchers have proposed syntax-driven rewrite rules and machine learning algorithms for inferring such predicates. However, these techniques suffer from two limitations. First, they do not let the optimizer constrain the set of columns that may be used in the learned predicate. Second, machine learning algorithms do not guarantee that the learned predicate preserves semantics. In this paper, we present SIA, a system for learning predicates while being guided by counter-examples and a verification technique, that addresses these limitations. The key idea is to leverage satisfiability modulo theories to generate counter-examples and use them to iteratively learn a valid, optimal predicate. We formalize this problem by proving the key properties of synthesized predicates. We implement our approach in SIA and evaluate its efficacy and efficiency. We demonstrate that it synthesizes a larger set of valid predicates compared to prior approaches. On a collection of 200 queries derived from the TPC-H benchmark, SIA successfully rewrites 114 queries with learned predicates. 66 of these rewritten queries exhibit more than 2X speed up.