State-machine replication for planet-scale systems

Online applications now routinely replicate their data at multiple sites around the world. In this paper we present Atlas, the first state-machine replication protocol tailored for such planet-scale systems. Atlas does not rely on a distinguished leader, so clients enjoy the same quality of service independently of their geographical locations. Furthermore, client-perceived latency improves as we add sites closer to clients. To achieve this, Atlas minimizes the size of its quorums using an observation that concurrent data center failures are rare. It also processes a high percentage of accesses in a single round trip, even when these conflict. We experimentally demonstrate that Atlas consistently outperforms state-of-The-Art protocols in planet-scale scenarios. In particular, Atlas is up to two times faster than Flexible Paxos with identical failure assumptions, and more than doubles the performance of Egalitarian Paxos in the YCSB benchmark.H2020 - Horizon 2020 Framework Programme(825184

Performance comparison of clustered and replicated information retrieval systems

The amount of information available over the Internet is increasing daily as well as the importance and magnitude of Web search engines. Systems based on a single centralised index present several problems (such as lack of scalability), which lead to the use of distributed information retrieval systems to effectively search for and locate the required information. A distributed retrieval system can be clustered and/or replicated. In this paper, using simulations, we present a detailed performance analysis, both in terms of throughput and response time, of a clustered system compared to a replicated system. In addition, we consider the effect of changes in the query topics over time. We show that the performance obtained for a clustered system does not improve the performance obtained by the best replicated system. Indeed, the main advantage of a clustered system is the reduction of network traffic. However, the use of a switched network eliminates the bottleneck in the network, markedly improving the performance of the replicated systems. Moreover, we illustrate the negative performance effect of the changes over time in the query topics when a distributed clustered system is used. On the contrary, the performance of a distributed replicated system is query independent

Space exploration: The interstellar goal and Titan demonstration

Automated interstellar space exploration is reviewed. The Titan demonstration mission is discussed. Remote sensing and automated modeling are considered. Nuclear electric propulsion, main orbiting spacecraft, lander/rover, subsatellites, atmospheric probes, powered air vehicles, and a surface science network comprise mission component concepts. Machine, intelligence in space exploration is discussed

IDEA: An Infrastructure for Detection-based Adaptive Consistency Control in Replicated Services

In Internet-scale distributed systems, replication-based scheme has been widely deployed to increase the availability and efficiency of services. Hence, consistency maintenance among replicas becomes an important research issue because poor consistency results in poor QoS or even monetary loss. Recent research in this area focuses on enforcing a certain consistency level, instead of perfect consistency, to strike a balance between consistency guarantee and system’s scalability. In this paper, we argue that, besides balancing consistency and scalability, it is equally, if not more, important to achieve adaptability of consistency maintenance. I.e., the system adjusts its consistency level on the fly to suit applications’ ongoing need. This paper then presents the design, implementation, and evaluation of IDEA (an Infrastructure for DEtection-based Adaptive consistency control), which adaptively controls consistency in replicated services by utilizing an inconsistency detection framework that detects inconsistency among nodes in a timely manner. Besides, IDEA achieves high performance of inconsistency resolution in terms of resolution delay. Through two emulated distribution application on Planet-Lab, IDEA is evaluated from two aspects: its adaptive interface and its performance of inconsistency resolution. According the experimentation, IDEA achieves adaptability by adjusting the consistency level according to users’ preference on-demand. As for performance, IDEA achieves low inconsistency resolution delay and communication cost

The Local and the Global: Hokusai's Great Wave in Contemporary Product Design

This article examines the impact and significance of Hokusai’s so-called The Great Wave in contemporary product promotion and design. Arguably Japan’s first global brand, this influential 19th-century woodcut has been widely adopted to style and advertise a wide range of merchandise, most of it neither manufactured in Japan nor primarily dependent on the commodification of the Japanese aesthetic or locale. Interpretation of the varied contexts in which the distinctive cresting wave appears challenges essentialising narratives that see the modern adoption of such traditional non-Western motifs as expressions of Japonisme or Orientalism. Taking an interdisciplinary approach that brings to bear design and global studies theory, Guth instead focuses on how this highly adaptive motif, with its connotations of being both nowhere and everywhere, serves to mediate between the local and the global. Despite the ubiquity of The Great Wave in the commercial realm, to date there have been no studies of its cross-cultural significance. To carry out this project, Guth conducted extensive research into the merchandise on offer in museum shops and online websites, and among global brands such as Patagonia that have made use of the motif. Guth also interviewed designers and users of the products to assess the rationale for the choice of this form of branding and the degree to which awareness of its origins influenced purchases. Guth was invited to present this new research on the global commercial impact of Hokusai’s The Great Wave at an international conference on ‘Hokusai in Context’ in Berlin in 2011. The conference paper and resulting published essay were developed to form a chapter in a book-length investigation into the global iconicity of Hokusai’s wave from its creation to the present day. The book, Hokusai’s Great Wave: Biography of a global icon, will be published by University of Hawai’i Press in 2014

Economics and Engineering for Preserving Digital Content

Progress towards practical long-term preservation seems to be stalled. Preservationists cannot afford specially developed technology, but must exploit what is created for the marketplace. Economic and technical facts suggest that most preservation ork should be shifted from repository institutions to information producers and consumers. Prior publications describe solutions for all known conceptual challenges of preserving a single digital object, but do not deal with software development or scaling to large collections. Much of the document handling software needed is available. It has, however, not yet been selected, adapted, integrated, or deployed for digital preservation. The daily tools of both information producers and information consumers can be extended to embed preservation packaging without much burdening these users. We describe a practical strategy for detailed design and implementation. Document handling is intrinsically complicated because of human sensitivity to communication nuances. Our engineering section therefore starts by discussing how project managers can master the many pertinent details.

Designing a Planetary-Scale IMAP Service with Conflict-free Replicated Data Types

Modern geo-replicated software serving millions of users across the globe faces the consequences of the CAP dilemma, i.e., the inevitable conflicts that arise when multiple nodes accept writes on shared state. The underlying problem is commonly known as fault-tolerant multi-leader replica- tion; actively researched in the distributed systems and database communities. As a more recent theoretical framework, Conflict-free Replicated Data Types (CRDTs) propose a solution to this problem by offering a set of always converging primitives. However, modeling non-trivial system state with CRDT primitives is a challenging and error-prone task. In this work, we propose a solution for a geo-replicated online service with fault-tolerant multi-leader replication based on CRDTs. We chose IMAP as use case due to its prevalence and simplicity. Therefore, we modeled an IMAP-CRDT and verified its correctness with the interactive theorem prover Isabelle/HOL. In order to bridge the gap between theory and practice, we implemented an open-source proto- type pluto and an IMAP benchmark for write-intensive workloads. We evaluated our prototype against the standard IMAP server Dovecot on a multi-continent public cloud. The results ex- pose the limitations of Dovecot with respect to response time performance and replication lag. Our prototype was able to leverage its conceptual advantages and outperformed Dovecot. We find that our approach is promising when facing the multitude of potential concurrency bugs in development of systems at planetary scale