Jul 2026· Proceedings of the VLDB Endowment· Vol abs/2607.19679· 0 citations· 75 references
Computer Science
TL;DR
This paper benchmarks MV-based query rewriting by jointly evaluating enumeration, selection, and rewriting with a modular evaluation framework and by using controlled ablations, and introduces a cross-engine protocol allowing us to compare systems that expose only execution plans by contrasting native optimizer-level rewriting with portable SQL rewriting baselines when available.
Abstract
Materialized views (MVs) accelerate OLAP and data-warehouse workloads by precomputing reusable subexpressions, but practical MV-based query acceleration is a multi-stage pipeline: candidate enumeration, view selection under storage budgets, and query rewriting inside the optimizer. Existing evaluations typically study only parts of this pipeline and within a single system, leaving end-to-end trade-offs and cross-system behavior unclear.
In this paper, we benchmark MV-based query rewriting by jointly evaluating enumeration, selection, and rewriting with a modular evaluation framework and by using controlled ablations. We also introduce a cross-engine protocol allowing us to compare systems that expose only execution plans by contrasting native optimizer-level rewriting with portable SQL rewriting baselines when available. Across representative academic methods and modern open-source and commercial systems, we find strong interaction effects across stages and large variability in MV usage and realized savings. We identify recurring failure modes that explain performance regressions after rewriting. Our results highlight which pipeline stages most often limit performance and provide evidence to guide future MV enumeration, selection, and rewriting designs.
DAGSmith is introduced, to the best of the authors' knowledge the first holistic dependency-aware source-to-source rewriting system for SQL pipeline DAGs and enables dependency-edge simplification, non-local semantic reuse, downstream-aware pruning, pipeline-aware work placement, rewrite-materialization co-optimization, and frequency-aware optimization.
Querying across heterogeneous data models incurs substantial overhead from query decomposition, data transfer, and processing outside the underlying database systems. We show that, in the evaluated decomposition-based architecture, a substantial part of this cross-model tax is not inherent to heterogeneity itself, but results from avoidable decisions made by the unifying query processor. We present a mapping- and capability-aware optimization approach that systematically moves processing closer to the data. It combines model-aware predicate pushdown, cross-model dependent joins, and non-redundant query-part construction within a unified optimization pipeline applicable across relational, document, and graph databases. The approach is implemented in MM-quecat and evaluated over PostgreSQL, MongoDB, Neo4j, and their heterogeneous combination. It reduces query latency by up to two orders of magnitude, eliminates all out-of-memory failures observed in the original single-DBMS experiments, provides further order-of-magnitude improvements through dependent execution, and reduces planning time for complex graph plans from hundreds of milliseconds to several milliseconds. The results demonstrate that established optimization principles can be generalized across data-model and system boundaries and can substantially improve the efficiency and robustness of decomposition-based multi-model query processing.
BatchDAG is a general-purpose orchestration layer that replaces multiple hand-engineered workflows with a single system that generates the appropriate execution strategy from natural language, and is not primarily an accuracy improvement over hand-optimized pipelines.
LLM-QOpt++ is presented, a novel hybrid, confidence-aware query optimization framework that unifies traditional CBO estimation, machine learning–based cost prediction, and large language model (LLM) reasoning within a single adaptive pipeline.