Low-latency, query-driven analytics over voluminous multidimensional, spatiotemporal datasets

2017 Summer.Includes bibliographical references.Ubiquitous data collection from sources such as remote sensing equipment, networked observational devices, location-based services, and sales tracking has led to the accumulation of voluminous datasets; IDC projects that by 2020 we will generate 40 zettabytes of data per year, while Gartner and ABI estimate 20-35 billion new devices will be connected to the Internet in the same time frame. The storage and processing requirements of these datasets far exceed the capabilities of modern computing hardware, which has led to the development of distributed storage frameworks that can scale out by assimilating more computing resources as necessary. While challenging in its own right, storing and managing voluminous datasets is only the precursor to a broader field of study: extracting knowledge, insights, and relationships from the underlying datasets. The basic building block of this knowledge discovery process is analytic queries, encompassing both query instrumentation and evaluation. This dissertation is centered around query-driven exploratory and predictive analytics over voluminous, multidimensional datasets. Both of these types of analysis represent a higher-level abstraction over classical query models; rather than indexing every discrete value for subsequent retrieval, our framework autonomously learns the relationships and interactions between dimensions in the dataset (including time series and geospatial aspects), and makes the information readily available to users. This functionality includes statistical synopses, correlation analysis, hypothesis testing, probabilistic structures, and predictive models that not only enable the discovery of nuanced relationships between dimensions, but also allow future events and trends to be predicted. This requires specialized data structures and partitioning algorithms, along with adaptive reductions in the search space and management of the inherent trade-off between timeliness and accuracy. The algorithms presented in this dissertation were evaluated empirically on real-world geospatial time-series datasets in a production environment, and are broadly applicable across other storage frameworks

DCMS: A data analytics and management system for molecular simulation

Molecular Simulation (MS) is a powerful tool for studying physical/chemical features of large systems and has seen applications in many scientific and engineering domains. During the simulation process, the experiments generate a very large number of atoms and intend to observe their spatial and temporal relationships for scientific analysis. The sheer data volumes and their intensive interactions impose significant challenges for data accessing, managing, and analysis. To date, existing MS software systems fall short on storage and handling of MS data, mainly because of the missing of a platform to support applications that involve intensive data access and analytical process. In this paper, we present the database-centric molecular simulation (DCMS) system our team developed in the past few years. The main idea behind DCMS is to store MS data in a relational database management system (DBMS) to take advantage of the declarative query interface (i.e., SQL), data access methods, query processing, and optimization mechanisms of modern DBMSs. A unique challenge is to handle the analytical queries that are often compute-intensive. For that, we developed novel indexing and query processing strategies (including algorithms running on modern co-processors) as integrated components of the DBMS. As a result, researchers can upload and analyze their data using efficient functions implemented inside the DBMS. Index structures are generated to store analysis results that may be interesting to other users, so that the results are readily available without duplicating the analysis. We have developed a prototype of DCMS based on the PostgreSQL system and experiments using real MS data and workload show that DCMS significantly outperforms existing MS software systems. We also used it as a platform to test other data management issues such as security and compression

A Survey on Array Storage, Query Languages, and Systems

Since scientific investigation is one of the most important providers of massive amounts of ordered data, there is a renewed interest in array data processing in the context of Big Data. To the best of our knowledge, a unified resource that summarizes and analyzes array processing research over its long existence is currently missing. In this survey, we provide a guide for past, present, and future research in array processing. The survey is organized along three main topics. Array storage discusses all the aspects related to array partitioning into chunks. The identification of a reduced set of array operators to form the foundation for an array query language is analyzed across multiple such proposals. Lastly, we survey real systems for array processing. The result is a thorough survey on array data storage and processing that should be consulted by anyone interested in this research topic, independent of experience level. The survey is not complete though. We greatly appreciate pointers towards any work we might have forgotten to mention.Comment: 44 page

Efficient processing of raster and vector data

[Abstract] In this work, we propose a framework to store and manage spatial data, which includes new efficient algorithms to perform operations accepting as input a raster dataset and a vector dataset. More concretely, we present algorithms for solving a spatial join between a raster and a vector dataset imposing a restriction on the values of the cells of the raster; and an algorithm for retrieving K objects of a vector dataset that overlap cells of a raster dataset, such that the K objects are those overlapping the highest (or lowest) cell values among all objects. The raster data is stored using a compact data structure, which can directly manipulate compressed data without the need for prior decompression. This leads to better running times and lower memory consumption. In our experimental evaluation comparing our solution to other baselines, we obtain the best space/time trade-offs.Ministerio de Ciencia, Innovación y Universidades; TIN2016-78011-C4-1-RMinisterio de Ciencia, Innovación y Universidades; TIN2016-77158 C4-3-RMinisterio de Ciencia, Innovación y Universidades; RTC-2017-5908-7Xunta de Galicia; ED431C 2017/58Xunta de Galicia; ED431G/01Xunta de Galicia; IN852A 2018/14University of Bío-Bío; 192119 2/RUniversity of Bío-Bío; 195119 GI/V

Exploiting Data Skew for Improved Query Performance

Analytic queries enable sophisticated large-scale data analysis within many commercial, scientific and medical domains today. Data skew is a ubiquitous feature of these real-world domains. In a retail database, some products are typically much more popular than others. In a text database, word frequencies follow a Zipf distribution with a small number of very common words, and a long tail of infrequent words. In a geographic database, some regions have much higher populations (and data measurements) than others. Current systems do not make the most of caches for exploiting skew. In particular, a whole cache line may remain cache resident even though only a small part of the cache line corresponds to a popular data item. In this paper, we propose a novel index structure for repositioning data items to concentrate popular items into the same cache lines. The net result is better spatial locality, and better utilization of limited cache resources. We develop a theoretical model for analyzing the cache behavior, and implement database operators that are efficient in the presence of skew. Our experiments on real and synthetic data show that exploiting skew can significantly improve in-memory query performance. In some cases, our techniques can speed up queries by over an order of magnitude

Compact data structures for large and complex datasets

Programa Oficial de Doutoramento en Computación . 5009V01[Abstract] In this thesis, we study the problem of processing large and complex collections of data, presenting new data structures and algorithms that allow us to efficiently store and analyze them. We focus on three main domains: processing of multidimensional data, representation of spatial information, and analysis of scientific data. The common nexus is the use of compact data structures, which combine in a unique data structure a compressed representation of the data and the structures to access such data. The target is to be able to manage data directly in compressed form, and in this way, to keep data always compressed, even in main memory. With this, we obtain two benefits: we can manage larger datasets in main memory and we take advantage of a better usage of the memory hierarchy. In the first part, we propose a compact data structure for multidimensional databases where the domains of each dimension are hierarchical. It allows efficient queries of aggregate information at different levels of each dimension. A typical application environment for our solution would be an OLAP system. Second, we focus on the representation of spatial information, specifically on raster data, which are commonly used in geographic information systems (GIS) to represent spatial attributes (such as the altitude of a terrain, the average temperature, etc.). The new method enables several typical spatial queries with better response times than the state of the art, at the same time that saves space in both main memory and disk. Besides, we also present a framework to run a spatial join between raster and vector datasets, that uses the compact data structure previously presented in this part of the thesis. Finally, we present a solution for the computation of empirical moments from a set of trajectories of a continuous time stochastic process observed in a given period of time. The empirical autocovariance function is an example of such operations. In this thesis, we propose a method that compresses sequences of floating numbers representing Brownian motion trajectories, although it can be used in other similar areas. In addition, we also introduce a new algorithm for the calculation of the autocovariance that uses a single trajectory at a time, instead of loading the whole dataset, reducing the memory consumption during the calculation process.[Resumo] Nesta tese estudamos o problema de procesar grandes coleccións de datos, presentando novas estruturas de datos compactas e algoritmos que nos permiten almacenalas e analizalas de forma eficiente. Centrámonos en tres dominios principais: procesamento de datos multidimensionais, representación de información espacial e análise de datos científicos. O nexo común é o uso de estruturas de datos compactas, que combinan nunha única estrutura de datos unha representación comprimida dos datos e as estruturas para acceder a tales datos. O obxectivo é poder manipular os datos directamente en forma comprimida, e desta maneira, manter os datos sempre comprimidos, incluso na memoria principal. Con esto obtemos dous beneficios: podemos xestionar conxuntos de datos máis grandes na memoria principal e aproveitar un mellor uso da xerarquía da memoria. Na primera parte propoñemos unha estructura de datos compacta para bases de datos multidimensionais onde os dominios de cada dimensión están xerarquizados. Permítenos consultar eficientemente a información agregada (sumar valor máximo, etc) a diferentes niveis de cada dimensión. Un entorno de aplicación típico para a nosa solución sería un sistema OLAP. En segundo lugar, centrámonos na representación de información espacial, especificamente en datos ráster, que se utilizan comunmente en sistemas de información xeográfica (SIX) para representar atributos espaciais (como a altitude dun terreo, a temperatura media, etc.). O novo método permite realizar eficientemente varias consultas espaciais típicas con tempos de resposta mellores que o estado da arte, ao mesmo tempo que reduce o espazo utilizado tanto na memoria principal como no disco. Ademais, tamén presentamos un marco de traballo para realizar un join espacial entre conxuntos de datos vectoriais e ráster, que usa a estructura de datos compacta previamente presentada nesta parte da tese. Por último, presentamos unha solución para o cálculo de momentos empíricos a partir dun conxunto de traxectorias dun proceso estocástico de tempo continuo observadas nun período de tempo dado. A función de autocovarianza empírica é un exemplo de tales operacións. Nesta tese propoñemos un método que comprime secuencias de números flotantes que representan traxectorias de movemento Browniano, aínda que pode ser empregado noutras áreas similares. Ademais, tamén introducimos un novo algoritmo para o cálculo da autocovarianza que emprega unha única traxectoria á vez, en lugar de cargar todo o conxunto de datos, reducindo o consumo de memoria durante o proceso de cálculo.[Resumen] En esta tesis estudiamos el problema de procesar grandes colecciones de datos, presentando nuevas estructuras de datos compactas y algoritmos que nos permiten almacenarlas y analizarlas de forma eficiente. Nos centramos principalmente en tres dominios: procesamiento de datos multidimensionales, representación de información espacial y análisis de datos científicos. El nexo común es el uso de estructuras de datos compactas, que combinan en una única estructura de datos una representación comprimida de los datos y las estructuras para acceder a dichos datos. El objetivo es poder manipular los datos directamente en forma comprimida, y de esta manera, mantener los datos siempre comprimidos, incluso en la memoria principal. Con esto obtenemos dos beneficios: podemos gestionar conjuntos de datos más grandes en la memoria principal y aprovechar un mejor uso de la jerarquía de la memoria. En la primera parte proponemos una estructura de datos compacta para bases de datos multidimensionales donde los dominios de cada dimensión están jerarquizados. Nos permite consultar eficientemente la información agregada (suma, valor máximo, etc.) a diferentes niveles de cada dimensión. Un entorno de aplicación típico para nuestra solución sería un sistema OLAP. En segundo lugar, nos centramos en la representación de la información espacial, específicamente en datos ráster, que se utilizan comúnmente en sistemas de información geográfica (SIG) para representar atributos espaciales (como la altitud de un terreno, la temperatura media, etc.). El nuevo método permite realizar eficientemente varias consultas espaciales típicas con tiempos de respuesta mejores que el estado del arte, al mismo tiempo que reduce el espacio utilizado tanto en la memoria principal como en el disco. Además, también presentamos un marco de trabajo para realizar un join espacial entre conjuntos de datos vectoriales y ráster, que usa la estructura de datos compacta previamente presentada en esta parte de la tesis. Por último, presentamos una solución para el cálculo de momentos empíricos a partir de un conjunto de trayectorias de un proceso estocástico de tiempo continuo observadas en un período de tiempo dado. La función de autocovariancia empírica es un ejemplo de tales operaciones. En esta tesis proponemos un método que comprime secuencias de números flotantes que representan trayectorias de movimiento Browniano, aunque puede ser utilizado en otras áreas similares. En esta parte, también introducimos un nuevo algoritmo para el cálculo de la autocovariancia que utiliza una única trayectoria a la vez, en lugar de cargar todo el conjunto de datos, reduciendo el consumo de memoria durante el proceso de cálculoXunta de Galicia; ED431G/01Ministerio de Economía y Competitividad ;TIN2016-78011-C4-1-RMinisterio de Economía y Competitividad; TIN2016-77158-C4-3-RMinisterio de Economía y Competitividad; TIN2013-46801-C4-3-RCentro para el desarrollo Tecnológico e Industrial; IDI-20141259Centro para el desarrollo Tecnológico e Industrial; ITC-20151247Xunta de Galicia; GRC2013/05