Auflistung nach Autor:in "Schaarschmidt, Michael"
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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.
- 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.