arXiv subjects

Hans-Arno Jacobsen

Publications and source records attributed to Hans-Arno Jacobsen.

85 records · Page 5Linked to original sources

arXiv2019

Parallel Index-based Stream Join on a Multicore CPU

There is increasing interest in using multicore processors to accelerate stream processing. For example, indexing sliding window content to enhance the performance of streaming queries is greatly improved by utilizing the computational capabilities of a multicore processor. However, designing an effective concurrency control mechanism that addresses the problem of concurrent indexing in highly dynamic settings remains a challenge. In this paper, we introduce an index data structure, called the Partitioned In-memory Merge-Tree, to address the challenges that arise when indexing highly dynamic data, which are common in streaming settings. To complement the index, we design an algorithm to realize a parallel index-based stream join that exploits the computational power of multicore processors. Our experiments using an octa-core processor show that our parallel stream join achieves up to 5.5 times higher throughput than a single-threaded approach.

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arXiv2018

PanJoin: A Partition-based Adaptive Stream Join

In stream processing, stream join is one of the critical sources of performance bottlenecks. The sliding-window-based stream join provides a precise result but consumes considerable computational resources. The current solutions lack support for the join predicates on large windows. These algorithms and their hardware accelerators are either limited to equi-join or use a nested loop join to process all the requests. In this paper, we present a new algorithm called PanJoin which has high throughput on large windows and supports both equi-join and non-equi-join. PanJoin implements three new data structures to reduce computations during the probing phase of stream join. We also implement the most hardware-friendly data structure, called BI-Sort, on FPGA. Our evaluation shows that PanJoin outperforms several recently proposed stream join methods by more than 1000x, and it also adapts well to highly skewed data.

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arXiv2018

Waveform Signal Entropy and Compression Study of Whole-Building Energy Datasets

Electrical energy consumption has been an ongoing research area since the coming of smart homes and Internet of Things devices. Consumption characteristics and usages profiles are directly influenced by building occupants and their interaction with electrical appliances. Extracted information from these data can be used to conserve energy and increase user comfort levels. Data analysis together with machine learning models can be utilized to extract valuable information for the benefit of occupants themselves, power plants, and grid operators. Public energy datasets provide a scientific foundation to develop and benchmark these algorithms and techniques. With datasets exceeding tens of terabytes, we present a novel study of five whole-building energy datasets with high sampling rates, their signal entropy, and how a well-calibrated measurement can have a significant effect on the overall storage requirements. We show that some datasets do not fully utilize the available measurement precision, therefore leaving potential accuracy and space savings untapped. We benchmark a comprehensive list of 365 file formats, transparent data transformations, and lossless compression algorithms. The primary goal is to reduce the overall dataset size while maintaining an easy-to-use file format and access API. We show that with careful selection of file format and encoding scheme, we can reduce the size of some datasets by up to 73%.

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arXiv2017

Real-time Load Prediction with High Velocity Smart Home Data Stream

This paper addresses the use of smart-home sensor streams for continuous prediction of energy loads of individual households which participate as an agent in local markets. We introduces a new device level energy consumption dataset recorded over three years wich includes high resolution energy measurements from electrical devices collected within a pilot program. Using data from that pilot, we analyze the applicability of various machine learning mechanisms for continuous load prediction. Specifically, we address short-term load prediction that is required for load balancing in electrical micro-grids. We report on the prediction performance and the computational requirements of a broad range of prediction mechanisms. Furthermore we present an architecture and experimental evaluation when this prediction is applied in the stream.

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arXiv2017

A Memory Bandwidth-Efficient Hybrid Radix Sort on GPUs

Sorting is at the core of many database operations, such as index creation, sort-merge joins, and user-requested output sorting. As GPUs are emerging as a promising platform to accelerate various operations, sorting on GPUs becomes a viable endeavour. Over the past few years, several improvements have been proposed for sorting on GPUs, leading to the first radix sort implementations that achieve a sorting rate of over one billion 32-bit keys per second. Yet, state-of-the-art approaches are heavily memory bandwidth-bound, as they require substantially more memory transfers than their CPU-based counterparts. Our work proposes a novel approach that almost halves the amount of memory transfers and, therefore, considerably lifts the memory bandwidth limitation. Being able to sort two gigabytes of eight-byte records in as little as 50 milliseconds, our approach achieves a 2.32-fold improvement over the state-of-the-art GPU-based radix sort for uniform distributions, sustaining a minimum speed-up of no less than a factor of 1.66 for skewed distributions. To address inputs that either do not reside on the GPU or exceed the available device memory, we build on our efficient GPU sorting approach with a pipelined heterogeneous sorting algorithm that mitigates the overhead associated with PCIe data transfers. Comparing the end-to-end sorting performance to the state-of-the-art CPU-based radix sort running 16 threads, our heterogeneous approach achieves a 2.06-fold and a 1.53-fold improvement for sorting 64 GB key-value pairs with a skewed and a uniform distribution, respectively.

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arXiv2016

A Step towards Advanced Metering for the Smart Grid: A Survey of Energy Monitors

The smart grid initiative has encouraged utility companies worldwide to rollout new and smarter versions of energy meters. Before an extensive rollout, which is both labor-intensive and incurs high capital costs, consumers need to be incentivized to reap the long-term benefits of smart grid. Off-the-shelf energy monitors can provide consumers with an insight of such potential benefits. Since energy monitors are owned by the consumer, the consumer has greater control over data which significantly reduces privacy and data confidentiality concerns. We evaluate several existing energy monitors using an online technical survey and online product literature. For consumers, the use of different off-the-shelf energy monitors can help demonstrate the potential gains of smart grid. Our survey indicates a trend towards incorporation of state-of-the-art capabilities, like appliance level monitoring through load disaggregation in energy monitors, which can encourage effective consumer participation. Multiple sensor types and ratings allow some monitors to operate in various configurations and environments.

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arXiv2014

DualTable: A Hybrid Storage Model for Update Optimization in Hive

Hive is the most mature and prevalent data warehouse tool providing SQL-like interface in the Hadoop ecosystem. It is successfully used in many Internet companies and shows its value for big data processing in traditional industries. However, enterprise big data processing systems as in Smart Grid applications usually require complicated business logics and involve many data manipulation operations like updates and deletes. Hive cannot offer sufficient support for these while preserving high query performance. Hive using the Hadoop Distributed File System (HDFS) for storage cannot implement data manipulation efficiently and Hive on HBase suffers from poor query performance even though it can support faster data manipulation.There is a project based on Hive issue Hive-5317 to support update operations, but it has not been finished in Hive's latest version. Since this ACID compliant extension adopts same data storage format on HDFS, the update performance problem is not solved. In this paper, we propose a hybrid storage model called DualTable, which combines the efficient streaming reads of HDFS and the random write capability of HBase. Hive on DualTable provides better data manipulation support and preserves query performance at the same time. Experiments on a TPC-H data set and on a real smart grid data set show that Hive on DualTable is up to 10 times faster than Hive when executing update and delete operations.

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arXiv2014

DGFIndex for Smart Grid: Enhancing Hive with a Cost-Effective Multidimensional Range Index

In Smart Grid applications, as the number of deployed electric smart meters increases, massive amounts of valuable meter data is generated and collected every day. To enable reliable data collection and make business decisions fast, high throughput storage and high-performance analysis of massive meter data become crucial for grid companies. Considering the advantage of high efficiency, fault tolerance, and price-performance of Hadoop and Hive systems, they are frequently deployed as underlying platform for big data processing. However, in real business use cases, these data analysis applications typically involve multidimensional range queries (MDRQ) as well as batch reading and statistics on the meter data. While Hive is high-performance at complex data batch reading and analysis, it lacks efficient indexing techniques for MDRQ. In this paper, we propose DGFIndex, an index structure for Hive that efficiently supports MDRQ for massive meter data. DGFIndex divides the data space into cubes using the grid file technique. Unlike the existing indexes in Hive, which stores all combinations of multiple dimensions, DGFIndex only stores the information of cubes. This leads to smaller index size and faster query processing. Furthermore, with pre-computing user-defined aggregations of each cube, DGFIndex only needs to access the boundary region for aggregation query. Our comprehensive experiments show that DGFIndex can save significant disk space in comparison with the existing indexes in Hive and the query performance with DGFIndex is 2-50 times faster than existing indexes in Hive and HadoopDB for aggregation query, 2-5 times faster than both for non-aggregation query, 2-75 times faster than scanning the whole table in different query selectivity.

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arXiv2014

Household Electricity Demand Forecasting -- Benchmarking State-of-the-Art Methods

The increasing use of renewable energy sources with variable output, such as solar photovoltaic and wind power generation, calls for Smart Grids that effectively manage flexible loads and energy storage. The ability to forecast consumption at different locations in distribution systems will be a key capability of Smart Grids. The goal of this paper is to benchmark state-of-the-art methods for forecasting electricity demand on the household level across different granularities and time scales in an explorative way, thereby revealing potential shortcomings and find promising directions for future research in this area. We apply a number of forecasting methods including ARIMA, neural networks, and exponential smoothening using several strategies for training data selection, in particular day type and sliding window based strategies. We consider forecasting horizons ranging between 15 minutes and 24 hours. Our evaluation is based on two data sets containing the power usage of individual appliances at second time granularity collected over the course of several months. The results indicate that forecasting accuracy varies significantly depending on the choice of forecasting methods/strategy and the parameter configuration. Measured by the Mean Absolute Percentage Error (MAPE), the considered state-of-the-art forecasting methods rarely beat corresponding persistence forecasts. Overall, we observed MAPEs in the range between 5 and >100%. The average MAPE for the first data set was ~30%, while it was ~85% for the other data set. These results show big room for improvement. Based on the identified trends and experiences from our experiments, we contribute a detailed discussion of promising future research.

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arXiv2013

SDN-like: The Next Generation of Pub/Sub

Software-Defined Networking (SDN) has raised the boundaries of cloud computing by offering unparalleled levels of control and flexibility to system administrators over their virtualized environments. To properly embrace this new era of SDN-driven network architectures, the research community must not only consider the impact of SDN over the protocol stack, but also on its overlying networked applications. In this big ideas paper, we study the impact of SDN on the design of future message-oriented middleware, specifically pub/sub systems. We argue that key concepts put forth by SDN can be applied in a meaningful fashion to the next generation of pub/sub systems. First, pub/sub can adopt a logically centralized controller model for maintenance, monitoring, and control of the overlay network. We establish a parallel with existing work on centralized pub/sub routing and discuss how the logically centralized controller model can be implemented in a distributed manner. Second, we investigate the separation of the control and data plane, which is integral to SDN, which can be adopted to raise the level of decoupling in pub/sub. We introduce a new model of pub/sub which separates the traditional publisher and subscriber roles into flow regulators and producer/consumers of data. We then present use cases that benefit from this approach and study the impact of decoupling for performance.

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arXiv2012

Solving Big Data Challenges for Enterprise Application Performance Management

As the complexity of enterprise systems increases, the need for monitoring and analyzing such systems also grows. A number of companies have built sophisticated monitoring tools that go far beyond simple resource utilization reports. For example, based on instrumentation and specialized APIs, it is now possible to monitor single method invocations and trace individual transactions across geographically distributed systems. This high-level of detail enables more precise forms of analysis and prediction but comes at the price of high data rates (i.e., big data). To maximize the benefit of data monitoring, the data has to be stored for an extended period of time for ulterior analysis. This new wave of big data analytics imposes new challenges especially for the application performance monitoring systems. The monitoring data has to be stored in a system that can sustain the high data rates and at the same time enable an up-to-date view of the underlying infrastructure. With the advent of modern key-value stores, a variety of data storage systems have emerged that are built with a focus on scalability and high data rates as predominant in this monitoring use case. In this work, we present our experience and a comprehensive performance evaluation of six modern (open-source) data stores in the context of application performance monitoring as part of CA Technologies initiative. We evaluated these systems with data and workloads that can be found in application performance monitoring, as well as, on-line advertisement, power monitoring, and many other use cases. We present our insights not only as performance results but also as lessons learned and our experience relating to the setup and configuration complexity of these data stores in an industry setting.

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arXiv2003

I know what you mean: semantic issues in Internet-scale publish/subscribe systems

In recent years, the amount of information on the Internet has increased exponentially developing great interest in selective information dissemination systems. The publish/subscribe paradigm is particularly suited for designing systems for routing information and requests according to their content throughout wide-area network of brokers. Current publish/subscribe systems use limited syntax-based content routing but since publishers and subscribers are anonymous and decoupled in time, space and location, often over wide-area network boundary, they do not necessarily speak the same language. Consequently, adding semantics to current publish/subscribe systems is important. In this paper we identify and examine the issues in developing semantic-based content routing for publish/subscribe broker networks.

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arXiv2003

S-ToPSS: Semantic Toronto Publish/Subscribe System

The increase in the amount of data on the Internet has led to the development of a new generation of applications based on selective information dissemination where, data is distributed only to interested clients. Such applications require a new middleware architecture that can efficiently match user interests with available information. Middleware that can satisfy this requirement include event-based architectures such as publish-subscribe systems. In this demonstration paper we address the problem of semantic matching. We investigate how current publish/subscribe systems can be extended with semantic capabilities. Our main contribution is the development and validation (through demonstration) of a semantic pub/sub system prototype S-ToPSS (Semantic Toronto Publish/Subscribe System).

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