The propagation of Internet-of-Things (IoT) sensors aboard moving objects has led to continuous spatiotemporal data streams that demand on-device, low-latency analysis. However, the underlying systems for processing this streaming data are ill-prepared. On the one hand, common stream processing engines lack support for spatiotemporal operations. On the other hand, existing libraries for spatiotemporal data are optimized for historical data rather than real-time processing. To bridge this gap, we present MobilityNebula, an integration between MEOS (Mobility Engine Open Source), a lightweight C library for spatiotemporal data management, and NebulaStream, a stream processing system designed for the edge-fog-cloud continuum. We evaluated MobilityNebula by deploying the system on edge devices, ingesting data from the Belgian railway operator (SNCB) trains, and performing real-time geospatial processing for point-based queries.

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.

Internet of Things (IoT) applications make use of live data from numerous sensors that reside outside cloud datacenters. As a result, it is imperative for IoT data management systems to reduce their network footprint while simultaneously scaling to larger numbers of sensors. One way of achieving this is to adapt data generation to the rate of changes in the real world. In this systems paper, we propose Chameleon, a sensor-driven protocol for network-efficient data management that treats sensors as first-class components of a stream processing system. Chameleon combines local knowledge from the sensors with global knowledge from the cloud to improve data acquisition. Our empirical evaluation shows that systems employing Chameleon outperform baselines for aggregate queries by up to one order of magnitude in terms of network utilization while keeping query re-sults similar with negligible difference (down to 0.8%) from base-lines. Chameleon enables data management systems to handle up to 80% more sensors without needing extra network resources.

Window joins (WJs) are fundamental operators in stream processing systems (SPSs), enabling continuous, time-aware joins over unbounded data streams. Unlike time-agnostic relational joins, WJs incorporate temporal semantics associated with different window types (i.e., sliding, session, and interval windows), which introduce uncertainty in algebraic properties such as commutativity and associativity. As a result, state-of-the-art SPSs exploit only a single, fixed join order, which limits optimization opportunities and often leads to suboptimal performance. In this work, we eliminate this restriction by introducing three transformation rules that enable WJ reordering while preserving query semantics for those window types. Based on them, we propose WJR , an algorithm that systematically enumerates semantically equivalent join orders, expanding the search space for finding efficient WJ execution plans. Our evaluation shows speedups of up to 10 for multi-way WJ queries under various window configurations and rate ratios, highlighting the performance benefits of flexible join reordering in streaming queries.

Engineering high-performance query execution engines is a challenging task. Query compilation provides excellent performance, but at the same time introduces significant system complexity, as it makes the engine hard to build, debug, and maintain. To overcome this complexity, we propose Nautilus, a framework that combines the ease of use of query interpretation and the performance of query compilation. On the one hand, Nautilus provides an interpretation-based operator interface that enables engineers to implement operators using imperative C++ code to ensure a familiar developer experience. On the other hand, Nautilus mitigates the performance drawbacks of interpretation by introducing a novel trace-based, multi-backend JIT compiler that translates operators into efficient code. As a result, Nautilus bridges the gap between compilation and interpretation and provides the best of both worlds, achieving high performance without sacrificing the productivity of engineers.

Today's IoT applications exploit the capabilities of three different computation environments: sensors, edge, and cloud. Ensuring fault tolerance at the edge level presents unique challenges due to complex network hierarchies and the presence of resource-constrained computing devices. In contrast to the Cloud, the Edge lacks high availability standards and a persistent upstream backup. To ensure reliability, fault tolerance mechanisms have to be deployed on the edge devices along with processing operators competing for available resources. However, existing operator placement strategies are not aware of fault tolerance resource requirements, and existing fault tolerance approaches are not aware of available resources. This miscommunication in resource-constrained environments like the Edge leads to underprovisioning and failures. In this paper, we present a resource-aware fault-tolerance approach that takes the unique characteristics of the Edge into account to provide reliable stream processing. To this end, we model fault tolerance as an operator placement problem that uses multi-objective optimization to decide where to backup data. As opposed to existing approaches that treat operator placement and fault tolerance as two separate steps, we combine them and showcase that this is especially important for low-end edge devices. Overall, our approach effectively mitigates potential failures and outperforms state-of-the-art fault tolerance approaches by up to an order of magnitude in throughput.

A recent trend in stream processing is offloading the computation of decomposable aggregation functions (DAF) from cloud nodes to geo-distributed fog/edge devices to decrease latency and improve energy efficiency. However, deploying DAFs on low-end devices is challenging due to their volatility and limited resources. Additionally, in geo-distributed fog/edge environments, creating new operator instances on demand and replicating operators ubiquitously is restricted, posing challenges for achieving load balancing without overloading devices. Existing work predominantly focuses on cloud environments, overlooking DAF operator placement in resource-constrained and unreliable geo-distributed settings. This paper presents NEMO, a resource-aware optimization approach that determines the replication factor and placement of DAF operators in resource-constrained geo-distributed topologies. Leveraging Euclidean embeddings of network topologies and a set of heuristics, NEMO scales to millions of nodes and handles topo-logical changes through adaptive re-placement and re-replication decisions. Compared to existing solutions, NEMO achieves up to 6× lower latency and up to 15× reduction in communication cost, while preventing overloaded nodes. Moreover, NEMO re-optimizes placements in constant time, regardless of the topology size. As a result, it lays the foundation to efficiently process continuous data streams on large, heterogeneous, and geo-distributed topologies.

Join ordering and query optimization are crucial for query performance but remain challenging due to unknown or changing characteristics of query intermediates, especially for complex queries with many joins. Over the past two decades, a spectrum of techniques for adaptive query processing (AQP)---including inter-/intra-operator adaptivity and tuple routing---have been proposed to address these challenges. However, commercial database systems in practice do not implement holistic AQP techniques because they increase the system complexity (e.g., intertwined planning and execution) and thus, complicate debugging and testing. Additionally, existing approaches may incur large overheads, leading to problematic performance regressions. In this paper, we introduce POLAR, a simple yet very effective technique for a self-regulating selection of alternative join orderings with bounded overhead. We enhance left-deep join pipelines with alternative join orders, perform regret-bounded tuple routing to find and validate "plans of least resistance", and then process the majority of tuple batches through these plans. We study different join order selection techniques, different routing strategies, and a variety of workload characteristics. Our experiments with a POLAR prototype in DuckDB show runtime improvements of up to 9x and less than 7% overhead for all benchmark queries, while outperforming state-of-the-art AQP systems by up to 15x.

With increasing main memory sizes, data processing has significantly shifted from secondary storage to main memory. However, choosing a good join order is still very important for efficient query execution in modern DBMS. This choice bases mainly on cardinality estimates for intermediate join results. However, the memory access pattern, e.g., sequential or random, on the intermediate state is an often neglected performance factor.

Data management systems will face several new challenges in supporting IoT applications during the coming years. These challenges arise from managing large numbers of heterogeneous IoT devices and require combining elastic cloud and fog resources in unified fog-cloud environments. In this demonstration, we introduce a smart city simulation called IoTropolis and use it to create interactive eHealth and Smart Grid application scenarios. We use these scenarios to showcase three key challenges of unified fog-cloud environments. Furthermore, we demonstrate how our recently proposed data management system for the IoT NebulaStream addresses these challenges. Visitors to our demonstration can configure and interact with the scenarios to manage electricity usage in IoTropolis or to distribute patients across different hospitals. Thereby, visitors can actively engage with the challenges showcased by IoTropolis and utilize NebulaStream to address them. As a result, our demonstration enables visitors to experience data management for future IoT applications.

Database management systems are facing growing data volumes. Previous research suggests that GPUs are well-equipped to quickly process joins and similar stateful operators, as GPUs feature high-bandwidth on-board memory. However, GPUs cannot scale joins to large data volumes due to two limiting factors: (1)~large state does not fit into the on-board memory, and (2)~spilling state to main memory is constrained by the interconnect bandwidth. Thus, CPUs are often the better choice for scalable data processing.

Remote Direct Memory Access (RDMA) hardware has bridged the gap between network and main memory speed and thus invalidated the common assumption that network is often the bottleneck in distributed data processing systems. However, high-speed networks do not provide "plug-and-play" performance (e.g., using IP-over- InfiniBand) and require a careful co-design of system and application logic. As a result, system designers need to rethink the architecture of their data management systems to benefit from RDMA acceleration. In this paper, we focus on the acceleration of stream processing engines, which is challenged by real-time constraints and state consistency guarantees. To this end, we propose Slash, a novel stream processing engine that uses high-speed networks and RDMA to efficiently execute distributed streaming computations. Slash embraces a processing model suited for RDMA acceleration and scales out by omitting the expensive data re-partitioning demands of scale-out SPEs. While scale-out SPEs rely on data re-partitioning to execute a query over many nodes, Slash uses RDMA to share mutable state among nodes. Overall, Slash achieves a throughput improvement up to two orders of magnitude over existing systems deployed on an InfiniBand network. Furthermore, it is up to a factor of 22 faster than a self-developed solution that relies on RDMA-based data re-partitioning to scale out query processing.

The Internet of Things (IoT) combines large data centers with (mobile, networked) edge devices that are constrained both in compute power and energy budget. Modern edge devices contribute to query processing by leveraging accelerated processing units with multicore CPUs or GPUs. Therefore, data processing in the IoT presents the challenges of 1) minimizing the energy consumed while sustaining a given query throughput, and 2) processing increasingly complex queries within a given energy budget.

The intra-window join (IaWJ), i.e., joining two input streams over a single window, is a core operation in modern stream processing applications. This paper presents the first comprehensive study on parallelizing the IaWJ on modern multicore architectures. In particular, we classify IaWJ algorithms into lazy and eager execution approaches. For each approach, there are further design aspects to consider, including different join methods and partitioning schemes, leading to a large design space. Our results show that none of the algorithms always performs the best, and the choice of the most performant algorithm depends on: (i) workload characteristics, (ii) application requirements, and (iii) hardware architectures. Based on the evaluation results, we propose a decision tree that can guide the selection of an appropriate algorithm.

Data science workflows are largely exploratory, dealing with under-specified objectives, open-ended problems, and unknown business value. Therefore, little investment is made in systematic acquisition, integration, and pre-processing of data. This lack of infrastructure results in redundant manual effort and computation. Furthermore, central data consolidation is not always technically or economically desirable or even feasible (e.g., due to privacy, and/or data ownership). The ExDRa system aims to provide system infrastructure for this exploratory data science process on federated and heterogeneous, raw data sources. Technical focus areas include (1) ad-hoc and federated data integration on raw data, (2) data organization and reuse of intermediates, and (3) optimization of the data science lifecycle, under awareness of partially accessible data. In this paper, we describe use cases, the overall system architecture, selected features of SystemDS' new federated backend (for federated linear algebra programs, federated parameter servers, and federated data preparation), as well as promising initial results. Beyond existing work on federated learning, ExDRa focuses on enterprise federated ML and related data pre-processing challenges. In this context, federated ML has the potential to create a more fine-grained spectrum of data ownership and thus, even new markets.

Today's users of data processing systems come from different domains, have different levels of expertise, and prefer different programming languages. As a result, analytical workload requirements shifted from relational to polyglot queries involving user-defined functions (UDFs). Although some data processing systems support polyglot queries, they often embed third-party language runtimes. This embedding induces a high performance overhead, as it causes additional data materialization between execution engines. In this paper, we present Babelfish, a novel data processing engine designed for polyglot queries. Babelfish introduces an intermediate representation that unifies queries from different implementation languages. This enables new, holistic optimizations across operator and language boundaries, e.g., operator fusion and workload specialization. As a result, Babelfish avoids data transfers and enables efficient utilization of hardware resources. Our evaluation shows that Babelfish outperforms state-of-the-art data processing systems by up to one order of magnitude and reaches the performance of handwritten code. With Babelfish, we bridge the performance gap between relational and multi-language UDFs and lay the foundation for the efficient execution of future polyglot workloads.

Stream Processing Engines (SPEs) execute long-running queries on unbounded data streams. They follow an interpretation-based processing model and do not perform runtime optimizations. This limits the utilization of modern hardware and neglects changing data characteristics at runtime. In this paper, we present Grizzly, a novel adaptive query compilation-based SPE, to enable highly efficient query execution. We extend query compilation and task-based parallelization for the unique requirements of stream processing and apply adaptive compilation to enable runtime re-optimizations. The combination of light-weight statistic gathering with just-in-time compilation enables Grizzly to adjust to changing data-characteristics dynamically at runtime. Our experiments show that Grizzly outperforms state-of-the-art SPEs by up to an order of magnitude in throughput.

GPUs have long been discussed as accelerators for database query processing because of their high processing power and memory bandwidth. However, two main challenges limit the utility of GPUs for large-scale data processing: (1) the on-board memory capacity is too small to store large data sets, yet (2) the interconnect bandwidth to CPU main-memory is insufficient for ad hoc data transfers. As a result, GPU-based systems and algorithms run into a transfer bottleneck and do not scale to large data sets. In practice, CPUs process large-scale data faster than GPUs with current technology. In this paper, we investigate how a fast interconnect can resolve these scalability limitations using the example of NVLink 2.0. NVLink 2.0 is a new interconnect technology that links dedicated GPUs to a [email protected] The high bandwidth of NVLink 2.0 enables us to overcome the transfer bottleneck and to efficiently process large data sets stored in main-memory on GPUs. We perform an in-depth analysis of NVLink 2.0 and show how we can scale a no-partitioning hash join beyond the limits of GPU memory. Our evaluation shows speed-ups of up to 18x over PCI-e 3.0 and up to 7.3x over an optimized CPU implementation. Fast GPU interconnects thus enable GPUs to efficiently accelerate query processing.

Scale-out stream processing engines (SPEs) are powering large big data applications on high velocity data streams. Industrial setups require SPEs to sustain outages, varying data rates, and low-latency processing. SPEs need to transparently reconfigure stateful queries during runtime. However, state-of-the-art SPEs are not ready yet to handle on-the-fly reconfigurations of queries with terabytes of state due to three problems. These are network overhead for state migration, consistency, and overhead on data processing. In this paper, we propose Rhino, a library for efficient reconfigurations of running queries in the presence of very large distributed state. Rhino provides a handover protocol and a state migration protocol to consistently and efficiently migrate stream processing among servers. Overall, our evaluation shows that Rhino scales with state sizes of up to TBs, reconfigures a running query 15 times faster than the state-of-the-art, and reduces latency by three orders of magnitude upon a reconfiguration.

Hash aggregation is an important data processing primitive which can be significantly accelerated by modern graphics processors (GPUs). Previous work derived heuristics for GPU-accelerated hash aggregation from the study of a particular GPU. In this paper, we examine the influence of different execution parameters on GPU-accelerated hash aggregation on four NVIDIA and two AMD GPUs based on six different microarchitectures. While we are able to replicate some of the previous results, our main finding is that optimal execution parameters are highly GPU-dependent. Most importantly, execution parameters optimized for a specific GPU are up to 21x slower on other GPUs. Given this hardware dependency, we present an algorithm to optimize execution parameters at runtime. On average, our algorithm converges on a result in less than 1% of the time required for a full evaluation of the search space. In this time, it finds execution parameters that are at most 1% slower than the optimum in 90% of our experiments. In the worst case, our algorithm finds execution parameters that are at most 1.29x slower than the optimum.

Modern Stream Processing Engines (SPEs) process large data volumes under tight latency constraints. Many SPEs execute processing pipelines using message passing on shared-nothing architectures and apply a partition-based scale-out strategy to handle high-velocity input streams. Furthermore, many state-of-the-art SPEs rely on a Java Virtual Machine to achieve platform independence and speed up system development by abstracting from the underlying hardware. In this paper, we show that taking the underlying hardware into account is essential to exploit modern hardware efficiently. To this end, we conduct an extensive experimental analysis of current SPEs and SPE design alternatives optimized for modern hardware. Our analysis highlights potential bottlenecks and reveals that state-of-the-art SPEs are not capable of fully exploiting current and emerging hardware trends, such as multi-core processors and high-speed networks. Based on our analysis, we describe a set of design changes to the common architecture of SPEs to scale-up on modern hardware. We show that the single-node throughput can be increased by up to two orders of magnitude compared to state-of-the-art SPEs by applying specialized code generation, fusing operators, batch-style parallelization strategies, and optimized windowing. This speedup allows for deploying typical streaming applications on a single or a few nodes instead of large clusters.

k-Means is a versatile clustering algorithm widely-used in practice. To cluster large data sets, state-of-the-art implementations use GPUs to shorten the data to knowledge time. These implementations commonly assign points on a GPU and update centroids on a CPU.

Progressive optimization introduces robustness for database workloads against wrong estimates, skewed data, correlated attributes, or outdated statistics. Previous work focuses on cardinality estimates and rely on expensive counting methods as well as complex learning algorithms. In this paper, we utilize performance counters to drive progressive optimization during query execution. The main advantages are that performance counters introduce virtually no costs on modern CPUs and their usage enables a non-invasive monitoring. We present fine-grained cost models to detect differences between estimates and actual costs which enables us to kick-start reoptimization. Based on our cost models, we implement an optimization approach that estimates the individual selectivities of a multi-selection query efficiently. Furthermore, we are able to learn properties like sortedness, skew, or correlation during run-time. In our evaluation we show, that the overhead of our approach is negligible, while performance improvements are convincing. Using progressive optimization, we improve runtime up to a factor of three compared to average run-times and up to a factor of 4,5 compared to worst case run-times. As a result, we avoid costly operator execution orders and; thus, making query execution highly robust.

In this paper, we accelerate the processing of tree-based in-dex structures by using SIMD instructions. We adapt the B+-Tree and prefix B-Tree (trie) by changing the search al-gorithm on inner nodes from binary search to k-ary search. The k-ary search enables the use of SIMD instructions, which are commonly available on most modern processors today. The main challenge for using SIMD instructions on CPUs is their inherent requirement for consecutive memory loads. The data for one SIMD load instruction must be located in consecutive memory locations and cannot be scattered over the entire memory. The original layout of tree-based index structures does not satisfy this constraint and must be adapted to enable SIMD usage. Thus, we introduce two tree adaptations that satisfy the specific constraints of SIMD instructions. We present two di↵erent algorithms for trans-forming the original tree layout into a SIMD-friendly layout. Additionally, we introduce two SIMD-friendly search algo-rithms designed for the new layout. Our adapted B+-Tree speeds up search processes by a fac-tor of up to eight for small data types compared to the origi-nal B+-Tree using binary search. Furthermore, our adapted prefix B-Tree enables a high search performance even for larger data types. We report a constant 14 fold speedup and an 8 fold reduction in memory consumption compared to the original B+-Tree. 1.