Modern database systems are increasingly expected to support hybrid queries that combine traditional relational operators with vector-based similarity search enabling applications such as semantic search, contextual recommendations, and multimodal analytics. However, existing benchmarks target either purely relational workloads or isolated similarity search, leaving a gap in evaluating database systems that aim to integrate both. In this paper, we present RVBench , a benchmarking framework for evaluating hybrid relational–vector workloads. RVBench comes with a relational data model that adapts the real-world MediaWiki schema to include vector columns and provides a suite of parameterized SQL templates that interleave similarity search with traditional SQL operations. The framework supports multiple similarity semantics (neighbors based on top-$k$, rank intervals, and sampled ranks) and allows generating hybrid workloads to evaluate database systems on both performance and retrieval quality. We demonstrate RVBench by benchmarking and comparing PostgreSQL and other commercial databases with a reference implementation of the workloads to highlight key trade-offs in query execution strategies and accuracy.

We present Popper, a dataflow system for building Machine Learning (ML) workflows. A novel aspect of Popper is its built-in support for inflight error handling, which is crucial in developing effective ML workflows. Popper provides a convenient API that allows users to create and execute complex work-flows comprising traditional data processing operations (such as map, filter, and join) and user-defined error handlers. The latter enables inflight detection and correction of errors introduced by ML models in the workflows. Inside Popper, we model the workflow as a reactive dataflow, a directed cyclic graph, to achieve efficient execution through pipeline parallelization. We demonstrate the inflight error-handling capabilities of Popper, for which we have built a graphical interface, allowing users to specify workflows, visualize and interact with its reactive dataflow, and delve into the internals of Popper.

More and more data is produced outside the cloud by edge devices that provide basic processing capabilities. This trend enables a new class of data management systems that use both edge and cloud infrastructures for efficient data processing. Such systems push down operations by placing query operators close to the data-producing devices. A key challenge for these systems is handling the evolution of continuous queries and the dynamic changes in the infrastructure. In particular, frequent arrival or removal of queries and potential volatility of the infrastructure might invalidate or reduce the efficiency of previous operator placement decisions and thus might lead to constant, expensive re-optimizations of queries. These changes require new solutions for operator placement, which adjust existing placement decisions upon changes to the queries and infrastructure. In this paper, we propose ISQP, a framework that keeps the operator placements valid under query and infrastructure changes. ISQP performs a fine-grained identification of invalid operator placements and takes concurrent, incremental placement decisions to reduce the optimization time. ISQP works for arbitrary placement strategies, making it a general-purpose framework. Our evaluations show that ISQP reduces the optimization overhead by one order of magnitude compared to the baseline.

Fast and scalable data transfer is crucial in today's decentralized data ecosystems and data-driven applications. Example use cases include transferring data from operational systems to consolidated data warehouse environments, or from relational database systems to data lakes for exploratory data analysis or ML model training. Traditional data transfer approaches rely on efficient point-to-point connectors or general middleware with generic intermediate data representations. Physical environments (e.g., on-premise, cloud, or consumer nodes) also have become increasingly heterogeneous. Existing work still struggles to achieve both, fast and scalable data transfer as well as generality in terms of heterogeneous systems and environments. Hence, in this paper, we introduce a holistic data transfer framework. Our XDBC framework splits the data transfer pipeline into logical components and provides a wide variety of physical implementations for these components. This design allows a seamless integration of different systems as well as the automatic optimizations of data transfer configurations according to workload and environment characteristics. Our evaluation shows that XDBC outperforms state-of-the-art generic data transfer tools by up to 5x, while being on par with specialized approaches.

Data-sharing ecosystems connect providers, consumers, and intermediaries to facilitate the exchange and use of data for a wide range of downstream tasks. In sensitive domains such as healthcare, privacy is enforced as a hard constraint--any shared data must satisfy a minimum privacy threshold. However, among all masking configurations that meet this requirement, the utility of the masked data can vary significantly, posing a key challenge: how to efficiently select the optimal configuration that preserves maximum utility. This paper presents A egis , a middleware framework that selects optimal masking configurations for machine learning datasets with features and class labels. A egis incorporates a utility optimizer that minimizes predictive utility deviation --quantifying shifts in feature-label correlations due to masking. Our framework leverages limited data summaries (such as 1D histograms) or none to estimate the feature-label joint distribution, making it suitable for scenarios where raw data is inaccessible due to privacy restrictions. To achieve this, we propose a joint distribution estimator based on iterative proportional fitting, which allows supporting various feature-label correlation quantification methods such as mutual information, chi-square, or g3. Our experimental evaluation of real-world datasets shows that Aegis identifies optimal masking configurations over an order of magnitude faster, while the resulting masked datasets achieve predictive performance on downstream ML tasks on par with baseline approaches and complements privacy anonymization data masking techniques.

In today's data-driven world, organizations face increasing pressure to comply with data disclosure policies, which require data masking measures and robust access control mechanisms. This paper presents Mascara, a middleware for specifying and enforcing data disclosure policies. Mascara extends traditional access control mechanisms with data masking to support partial disclosure of sensitive data. We introduce data masks to specify disclosure policies flexibly and intuitively and propose a query modification approach to rewrite user queries into disclosure-compliant ones. We present a utility estimation framework to estimate the information loss of masked data based on relative entropy, which Mascara leverages to select the disclosure-compliant query that minimizes information loss. Our experimental evaluation shows that Mascara effectively chooses the best disclosure-compliant query with a success rate exceeding 90%, ensuring users get data with the lowest possible information loss. Additionally, Mascara's overhead compared to normal execution without data protection is negligible, staying lower than 300ms even for extreme scenarios with hundreds of possible disclosure-compliant queries.

Efficient data discovery is crucial in the era of data-driven decisionmaking. However, current practices face significant challenges due to the intricacies of identifying datasets with specific distributional characteristics, such as percentiles, when data repositories are decentralized. Traditional keyword-based search methods are insufficient for these complex requirements, often resulting in suboptimal dataset search results. To address these challenges, this paper presents Fainder, a fast and accurate index for "percentile predicates" on histogram-based data summaries, which streamlines the search process for datasets with specific distributional requirements. Fainder can be constructed on heterogeneous histogram collections and employs binary search in conjunction with multi-step pruning techniques to efficiently identify search results for percentile predicates. Thereby, it simplifies data provisioning and improves the effectiveness of dataset discovery. Empirical evaluation of our solution on three large-scale data repositories shows that Fainder is effective for distribution-aware dataset search and provides order-of-magnitude efficiency gains over baselines.

Today’s organizations utilize a plethora of heterogeneous and autonomous DBMSes, many of those being spread across different geo-locations. It is therefore crucial to have effective and efficient cross-database query processing capabilities. We present XDB, an efficient middleware system that runs cross-database analytics over existing DBMSes. In contrast to traditional query processing systems, XDB does not rely on any mediating execution engine to perform cross-database operations (e.g., joining data from two DBMSes). It delegates an entire query execution including cross-database operations to underlying DBMSes. At its core, it comprises an optimizer and a delegation engine: the optimizer rewrites cross-database queries into a delegation plan, which captures the semantics as well as the mechanics of a fully decentralized query execution; the delegation engine then deploys the plan to the underlying DBMSes via their declarative interfaces. Our experimental study based on the TPC-H benchmark data shows that XDB outperforms state-of-the-art systems (Garlic and Presto) by up to 6× in terms of runtime and up to 3 orders of magnitude in terms of data transfer.

Data are naturally produced at different locations and hence stored on different DBMSes. To maximize the value of the collected data, today's users combine data from different sources. Research in data integration has proposed the Mediator-Wrapper (MW) architecture to enable ad-hoc querying processing over multiple sources. The MW approach is desirable for users, as they do not need to deal with heterogeneous data sources. However, from a query processing perspective, the MW approach is inefficient: First, one needs to provision the mediating execution engine with resources. Second, during query processing, data gets "centralized" within the mediating engine, which causes redundant data movement. Recently, we proposed in-situ cross-database query processing , a paradigm for federated query processing without a mediating engine. Our approach optimizes runtime performance and reduces data movement by leveraging existing systems, eliminating the need for an additional federated query engine. In this demonstration, we showcase XDB, our prototype for in-situ cross-database query processing. We demonstrate several aspects of XDB, i.e. the cross-database environment, our optimization techniques, and its decentralized execution phase.

Continuous applications such as device monitoring and anomaly detection often require real-time aggregated statistics over unbounded data streams. While existing stream processing systems such as Flink, Spark, and Storm support processing of streaming aggregations, their optimizations are limited with respect to the dynamic nature of the data, and therefore are suboptimal when the workload changes and/or when there is data skew. In this paper we present AdCom, which is an adaptive combiner for stream processing engines. The use of AdCom in aggregation queries enables pre-aggregating tuples upstream (i.e., before data shuffling) followed by global aggregation downstream. In contrast to existing approaches, AdCom can automatically adjust the number of tuples to pre-aggregate depending on the data rate and available network. Our experimental study using real-world streaming workloads shows that using AdCom leads to 2.5-9× higher sustainable throughput without compromising latency.

In this paper, we address the problem of compliant geo-distributed query processing. In particular, we focus on dataflow policies that impose restrictions on movement of data across geographical or institutional borders. Traditional ways to distributed query processing do not consider such restrictions and therefore in geo-distributed environments may lead to non-compliant query execution plans. For example, an execution plan for a query over data sources from Europe, North America, and Asia, which may otherwise be optimal, may not comply with dataflow policies as a result of shipping some restricted (intermediate) data. We pose this problem of compliance in the setting of geo-distributed query processing. We propose a compliance-based query optimizer that takes into account dataflow policies, which are declaratively specified using our policy expressions, to generate compliant geo-distributed execution plans. Our experimental study using a geo-distributed adaptation of the TPC-H benchmark data indicates that our optimization techniques are effective in generating efficient compliant plans and incur low overhead on top of traditional query optimizers.

In this paper we present our work on compliant geo-distributed data processing. Our work focuses on the new dimension of dataflow constraints that regulate the movement of data across geographical or institutional borders. For example, European directives may regulate transferring only certain information fields (such as non personal information) or aggregated data. Thus, it is crucial for distributed data processing frameworks to consider compliance with respect to dataflow constraints derived from these regulations. We have developed a compliance-based data processing framework, which (i) allows for the declarative specification of dataflow constraints, (ii) determines if a query can be translated into a compliant distributed query execution plan, and (iii) executes the compliant plan over distributed SQL databases. We demonstrate our framework using a geo-distributed adaptation of the TPC-H benchmark data. Our framework provides an interactive dashboard, which allows users to specify dataflow constraints, and analyze and execute compliant distributed query execution plans.

International audience

Frequent sequence mining methods often make use of constraints to control which subsequences should be mined. A variety of such subsequence constraints has been studied in the literature, including length, gap, span, regular-expression, and hierarchy constraints. In this article, we show that many subsequence constraints—including and beyond those considered in the literature—can be unified in a single framework. A unified treatment allows researchers to study jointly many types of subsequence constraints (instead of each one individually) and helps to improve usability of pattern mining systems for practitioners. In more detail, we propose a set of simple and intuitive “pattern expressions” to describe subsequence constraints and explore algorithms for efficiently mining frequent subsequences under such general constraints. Our algorithms translate pattern expressions to succinct finite-state transducers, which we use as computational model, and simulate these transducers in a way suitable for frequent sequence mining. Our experimental study on real-world datasets indicates that our algorithms—although more general—are efficient and, when used for sequence mining with prior constraints studied in literature, competitive to (and in some cases superior to) state-of-the-art specialized methods.

Frequent sequence mining methods often make use of constraints to control which subsequences should be mined, e.g., length, gap, span, regular-expression, and hierarchy constraints. We show that many subsequence constraints-including and beyond those considered in the literature-can be unified in a single framework. In more detail, we propose a set of simple and intuitive "pattern expressions" to describe subsequence constraints and explore algorithms for efficiently mining frequent subsequences under such general constraints. A unified treatment allows researchers to study jointly many types of subsequence constraints (instead of each one individually) and helps to improve usability of pattern mining systems for practitioners.

We propose LASH, a scalable, distributed algorithm for mining sequential patterns in the presence of hierarchies. LASH takes as input a collection of sequences, each composed of items from some application-specific vocabulary. In contrast to traditional approaches to sequence mining, the items in the vocabulary are arranged in a hierarchy: both input sequences and sequential patterns may consist of items from different levels of the hierarchy. Such hierarchies naturally occur in a number of applications including mining natural-language text, customer transactions, error logs, or event sequences. LASH is the first parallel algorithm for mining frequent sequences with hierarchies; it is designed to scale to very large datasets. At its heart, LASH partitions the data using a novel, hierarchy-aware variant of item-based partitioning and subsequently mines each partition independently and in parallel using a customized mining algorithm called pivot sequence miner. LASH is amenable to a MapReduce implementation; we propose effective and efficient algorithms for both the construction and the actual mining of partitions. Our experimental study on large real-world datasets suggest good scalability and run-time efficiency.

Frequent sequence mining is one of the fundamental building blocks in data mining. While the problem has been extensively studied, few of the available techniques are sufficiently scalable to handle datasets with billions of sequences; such large-scale datasets arise, for instance, in text mining and session analysis. In this article, we propose MG-FSM, a scalable algorithm for frequent sequence mining on MapReduce. MG-FSM can handle so-called “gap constraints”, which can be used to limit the output to a controlled set of frequent sequences. Both positional and temporal gap constraints, as well as appropriate maximality and closedness constraints, are supported. At its heart, MG-FSM partitions the input database in a way that allows us to mine each partition independently using any existing frequent sequence mining algorithm. We introduce the notion of ω-equivalency, which is a generalization of the notion of a “projected database” used by many frequent pattern mining algorithms. We also present a number of optimization techniques that minimize partition size, and therefore computational and communication costs, while still maintaining correctness. Our experimental study in the contexts of text mining and session analysis suggests that MG-FSM is significantly more efficient and scalable than alternative approaches.