Auflistung nach Autor:in "Gessert, Felix"
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- KonferenzbeitragThe cache sketch: revisiting expiration-based caching in the age of cloud data management(Datenbanksysteme für Business, Technologie und Web (BTW 2015), 2015) Gessert, Felix; Schaarschmidt, Michael; Wingerath, Wolfram; Friedrich, Steffen; Ritter, NorbertThe expiration-based caching model of the web is generally considered irreconcilable with the dynamic workloads of cloud database services, where expiration dates are not known in advance. In this paper, we present the Cache Sketch data structure which makes expiration-based caching of database records feasible with rich tunable consistency guarantees. The Cache Sketch enables database services to leverage the large existing caching infrastructure of content delivery networks, browser caches and web caches to provide low latency and high scalability. The Cache Sketch employs Bloom filters to create compact representations of potentially stale records to transfer the task of cache coherence to clients. Furthermore, it also minimizes the number of invalidations the service has to perform on caches that support them (e.g., CDNs). With different age-control policies the Cache Sketch achieves very high cache hit ratios with arbitrarily low stale read probabilities. We present the Constrained Adaptive TTL Es- timator to provide cache expiration dates that optimize the performance of the Cache Sketch and invalidations. To quantify the performance gains and to derive workloadoptimal Cache Sketch parameters, we introduce the YCSB Monte-Carlo Caching Simulator (YMCA), a generic framework for simulating the performance and consistency characteristics of any caching and replication topology. We also provide empirical evidence for the efficiency of the Cache Sketch construction and the real-world latency reductions of database workloads under CDN-caching.
- KonferenzbeitragThe Case For Change Notifications in Pull-Based Databases(Datenbanksysteme für Business, Technologie und Web (BTW 2017) - Workshopband, 2017) Wingerath, Wolfram; Gessert, Felix; Friedrich, Steffen; Witt, Erik; Ritter, NorbertModern web applications often require application servers to deliver updates proactively to the client. These push-based architectures, however, are notoriously hard to implement on top of existing infrastructure, because today’s databases typically only support pull-based access to data. In this paper, we first illustrate the usefulness of query change notifications and the complexity of providing them. We then describe use cases and discuss state-of-the-art systems that do provide them, before we finally propose a system architecture that offers query change notifications as an opt-in feature for existing pull-based databases. As our proposed architecture distributes computational work across a cluster of machines, we also compare scalable stream processing frameworks that could be used to implement the proposed system design.
- TextdokumentNoSQL & Real-Time Data Management in Research & Practice(BTW 2019 – Workshopband, 2019) Wingerath, Wolfram; Gessert, Felix; Ritter, NorbertUsers have come to expect reactivity from mobile and web applications, i.e. they assume that changes made by other users become visible immediately. However, developers are challenged with building reactive applications on top of traditional pull-oriented databases, because they are ill-equipped to push new information to the client. Systems for data stream management and processing, on the other hand, are natively push-oriented and thus facilitate reactive behavior, but they do not follow the same collection-based semantics as traditional databases: Instead of database collections, stream-oriented systems are based on a notion of potentially unbounded sequences of data items. In this tutorial, we survey and categorize the system space between pull-oriented databases and push-oriented stream management systems, using their respectively facilitated means of data retrieval as a reference point. We start with an in-depth survey of the most relevant NoSQL databases to provide a comparative classification and highlight open challenges. To this end, we analyze the approach of each system to derive its scalability, availability, consistency, data modeling, and querying characteristics. We present how each system’s design is governed by a central set of trade-offs over irreconcilable system properties. We then cover recent research results in distributed data management to illustrate that some shortcomings of NoSQL systems could already be solved in practice, whereas other NoSQL data management problems pose interesting and unsolved research challenges. A particular emphasis lies on the novel system class of real-time databases which combine the push-based access paradigm of stream-oriented systems with the collection-based query semantics of traditional databases. We explore why real-time databases deserve distinction in a separate system class and dissect their different architectures to highlight issues, derive open challenges, and discuss avenues for addressing them.
- KonferenzbeitragNosql OLTP benchmarking: A survey(Informatik 2014, 2014) Friedrich, Steffen; Wingerath, Wolfram; Gessert, Felix; Ritter, NorbertIn recent years, various distributed NoSQL datastores have been developed that offer horizontal scalability and higher availability than traditional relational databases, but fewer querying options and only reduced consistency guarantees. The diversity of the design space makes it difficult to understand the performance implications of individual system designs. Existing benchmarking tools measure some relevant aspects, but do not capture all of them. In this paper, we give an overview of the state-of-the-art in NoSQL OLTP benchmarking, identify missing features as well as open challenges and point towards possible solutions.
- ZeitschriftenartikelPolyglot Persistence(Datenbank-Spektrum: Vol. 15, No. 3, 2015) Gessert, Felix; Ritter, Norbert
- KonferenzbeitragScalable Cloud Data Management Workshop (SCDM 2017)(Datenbanksysteme für Business, Technologie und Web (BTW 2017) - Workshopband, 2017) Gessert, Felix; Ritter, Norbert
- KonferenzbeitragScalable Data Management: An In-Depth Tutorial on NoSQL Data Stores(Datenbanksysteme für Business, Technologie und Web (BTW 2017) - Workshopband, 2017) Gessert, Felix; Wingerath, Wolfram; Ritter, NorbertThe unprecedented scale at which data is consumed and generated today has shown a large demand for scalable data management and given rise to non-relational, distributed “NoSQL” database systems. Two central problems triggered this process: 1) vast amounts of user-generated content in modern applications and the resulting request loads and data volumes as well as 2) the desire of the developer community to employ problem-specific data models for storage and querying. To address these needs, various data stores have been developed by both industry and research, arguing that the era of one-size-fits-all database systems is over. The heterogeneity and sheer amount of these systems – now commonly referred to as NoSQL data stores – make it increasingly di cult to select the most appropriate system for a given application. Therefore, these systems are frequently combined in polyglot persistence architectures to leverage each system in its respective sweet spot. This tutorial gives an in-depth survey of the most relevant NoSQL databases to provide comparative classification and highlight open challenges. To this end, we analyze the approach of each system to derive its scalability, availability, consistency, data modeling and querying characteristics. We present how each system’s design is governed by a central set of trade-o s over irreconcilable system properties. We then cover recent research results in distributed data management to illustrate that some shortcomings of NoSQL systems could already be solved in practice, whereas other NoSQL data management problems pose interesting and unsolved research challenges. In addition to earlier tutorials, we explicitly address how the quickly emerging topic of processing and storing massive amounts of data in real-time can be solved by di erent types real-time data management systems.
- KonferenzbeitragSkalierbare NoSQL- und Cloud-Datenbanken in Forschung und Praxis(Datenbanksysteme für Business, Technologie und Web (BTW 2015) - Workshopband, 2015) Gessert, Felix; Ritter, NorbertDie rasante Entwicklung nicht-relationaler, verteilter NoSQL Datenbanksysteme hat in den letzten Jahren einen beispiellosen Aufschwung erlebt. Zwei zentrale Probleme haben diesen Prozess angestoßen: die gewaltigen Mengen von User- ” generated-Content“ in modernen Anwendungen und die damit einhergehenden An- fragelasten und Datenvolumnia, sowie der Ruf von Entwicklern nach problemspezifischen Datenmodellen und Schemaflexibilität. Das Tutorium Skalierbare NoSQL- und ” Cloud-Datenbanken in Forschung und Praxis“ bietet einen umfassenden Überblick über die Konzepte und Techniken der relevantesten NoSQL- und Cloud-Datenbanken, mit einem besonderen Fokus auf Trade-Offs im Bereich Skalierbarkeit, Konsistenz und Anfragemächtigkeit. Es werden sowohl zugrundeliegende theoretische Konzepte, bahnbrechende wissenschaftliche Beiträge, als auch praktische Aspekte wie APIs, Lizenzund Pricingmodelle sowie Architekturen diskutiert.
- KonferenzbeitragTowards a scalable and unified REST API for cloud data stores(Informatik 2014, 2014) Gessert, Felix; Friedrich, Steffen; Wingerath, Wolfram; Schaarschmidt, Michael; Ritter, NorbertIn the last years, many database-as-a-service (DBaaS) systems have started to offer their functionalities through REST APIs. Examples are record stores like DynamoDB and Azure Tables, object stores such as Amazon S3 as well as many NoSQL database systems, for instance Riak, CouchDB and ElasticSearch. Yet today, there has been no systematic effort on deriving a unified REST interface which takes into account the different data models, schemas, consistency concepts, transactions, access-control mechanisms and query languages to expose cloud data stores through a common interface without restricting their functionality. This work motivates the design of such a REST API as well as the challenges of providing it in an extensible, scalable and highly-available fashion. To this end, we propose the REST middleware ORESTES that consists of an independently scalable tier of HTTP servers that map the unified REST API to aggregate-oriented (NoSQL) data stores. It extracts a wide range of DBaaS concerns (e.g. schema management and access control) and provides them in a modular, database-independent fashion at the middleware-level. To tackle the latency problem of cloud-based web applications we introduce the Bloom filter-bounded staleness cache consistency algorithm. It leverages the global web caching infrastructure for geo-replication to allow consistent low latency reads. We furthermore show the first steps towards a Polyglot Persistence Mediator that exploits the decoupling of the REST API from the data store to route data and operations based on SLAs.
- KonferenzbeitragTowards Automated Polyglot Persistence(Datenbanksysteme für Business, Technologie und Web (BTW 2015), 2015) Schaarschmidt, Michael; Gessert, Felix; Ritter, NorbertIn this paper, we present an innovative solution for providing automated polyglot persistence based on service level agreements defined over functional and non-functional requirements of database systems. Complex applications require polyglot persistence to deal with a wide range of database related needs. Until now, the overhead and the required know-how to manage multiple database systems prevents many applications from employing efficient polyglot persistence solutions. Instead, developers are often forced to implement one-size-fits-all solutions that do not scale well and cannot easily be upgraded. Therefore, we introduce the concept for a Polyglot Persistence Mediator (PPM), which allows for runtime decisions on routing data to different backends according to schema-based annotations. This enables applications to either employ polyglot persistence right from the beginning or employ new systems at any point with minimal overhead. We have implemented and evaluated the concept of automated polyglot persistence for a REST-based Database-as-a-Service setting. Evaluations were performed on various EC2 setups, showing a scalable writeperformance increase of 50-100\% for a typical polyglot persistence scenario as well as drastically reduced latencies for reads and queries.