713 research outputs found
The Case for Reconfiguration without Consensus: Comparing Algorithms for Atomic Storage
No full textWe compare different algorithms for reconfigurable atomic storage in the data-centric model. We present the first experimental evaluation of two recently proposed algorithms for reconfiguration without consensus and compare them to established algorithms for reconfiguration both with and without consensus.
Our evaluation reveals that the new algorithms offer a significant improvement in terms of latency and overhead for reconfiguration without consensus. Our evaluation also shows that reconfiguration without consensus, can obtain similar results to that of consensus-based reconfiguration, which relies on a stable leader. Moreover, the new algorithms also substantially reduces the overhead compared to consensus-based reconfiguration without a leader.
While our analysis confirms our intuition that batching reconfiguration requests serves to reduce the overhead of reconfigurations, our evaluation also shows that it is equally important to separate reconfigurations from read and write operations. Specifically, we found that using read and write operations to assist in completing concurrent reconfigurations is in fact detrimental to the reconfiguration performance
Space, Time, and Oil: The Global Petroleumscape
No full textIn addition to explaining the context in which this book emerged, Carola Hein introduces the concept of the petroleumscape, a layered physical and social landscape that reinforces itself over time through human action. The petroleumscape includes different types of interconnected spaces—industrial, administrative, retail, and infrastructural—that are usually considered separately. Hein makes clear why this volume’s case studies pay careful attention to what has been highlighted, downplayed, and hidden as corporate, state, and other relevant actors have attempted to shape perceptions of petroleum and the landscape of which it is a part. Hein also outlines five key stages in the petroleumscape’s development, beginning with the innovations in obtaining petroleum that took place in Pennsylvania in 1859, when petroleum served primarily as a source of lighting fluid, and ending with recent attempts to overcome petroleum dependence.History, Form & Aesthetic
Brief announcement: When you don't trust clients: Byzantine proposer fast Paxos
No full textState machine replication is a general approach for constructing fault-tolerant services, and a key protocol underlying state machine replication is consensus. The set of Byzantine failures is so large that it has been applied for masking the effects of compromised systems, and so Byzantine-tolerant consensus has been used to construct systems that are meant to ameliorate the effect of compromise (see [1] among others). In the Byzantine model, there is no trust among processes: any process can behave in an arbitrarily faulty manner. However, in multi-site systems, processes in the same administrative domain typically have a measure of mutual trust. This is because such processes share fate: for example, if a process in a domain is compromised, then other processes-perhaps all of them-can be compromised as well, and the local services they rely upon may be compromised. In [4], this observation was used to argue for the Mutually Suspicious Domain (MSD) model, in which there is mutual trust between processes in a domain, but no trust for inter-domain communication, i.e., processes within a domain must protect itself from possible uncivil behavior from processes in other domains. © 2011 Springer-Verlag
When you don't trust clients: Byzantine proposer fast Paxos
No full textWe derive a consensus protocol for a hybrid failure model. In this model, clients are Byzantine faulty and servers are crash faulty. We argue that this model is well suited to environments where the servers run within one administrative domain, and the clients run outside of this domain. Our consensus protocol, which is derived from crash Paxos, provides low latency for client requests, tolerates any number of (Byzantine) faulty clients, up to 1/3 (crash) faulty servers, and does not rely on computing costly signatures in the common case. It can be used to build state machine replication that provides a highly available service. © 2012 IEEE
The global petroleumscape of the Rotterdam/The Hague area: As a model for further research
No full textFlows of petroleum have shaped the built environment of industrial, retail, administrative, and ancillary spaces, of infrastructures and buildings, as well as their representation. Carola Hein analyses the spatial impact of petroleum on the sea-land continuum through the lens of the port city region of Rotterdam/The Hague.History, Form & Aesthetic
The What, Why, and How of Planning History
No full textThis introduction presents an overview of the key concepts discussed in the subsequent chapters of this book. The book investigates the history of planning since its emergence as a discipline in the mid-19th century. Planning is a complex discipline, with more than one body of terminology, multiple interpretations, and manifold applications through space and over time, and historians have commented on it from a variety of perspectives. The book focuses on English-language sources, and develops novel interdisciplinary, transcultural, and postcolonial approaches. It examines sites, dynamics, and typologies, and explores the state of the field—its achievements and shortcomings and future challenges. The book analyzes planning histories and historiographies while acknowledging the difficulties of comparing planning in a global setting. It explores spatial traditions and cultural landscapes—imagine folding and unfolding the world anew, as in the Dymaxion map made by the American architect Buckminster Fuller.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.OLD History of Architecture & Urban Plannin
Idioms of Japanese Planning Historiography
No full textIn this chapter, the authors highlight three important strands of interpretation in Japanese planning history—one studying planning as a part of a general urban or architectural history, one focusing on planning as a discipline, and another emphasizing urban design. These strands of history writing speak to the difficulties of studying a country with a very different language, plus a long-standing and original culture. The authors aim to position the planning history writing on Japan in the context of global networks of planning historiography. Exploring the planning history writing inside and outside of Japan, they see different idioms that are related to specific interpretations, terminologies, and representations or perceptions of planning, but also to the use of planning primary materials, written and in imagery. The different perceptions of the role of planning are embedded in, and effectively partly result from, different idioms, both in words and visualizations.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.History, Form & Aesthetic
Blankness: The Architectural Void of North Sea Energy Logistics
No full textEnergy logistics have contributed to the gradual transformation of the North Sea into an industrial void. Referring to the concept of blankness articulated by Roberto Mangabiera Unger and Jeffrey Kipnis, Nancy Couling and Carola Hein call for imaginative architectural interventions that respond to the potential of logistic spaces lodged within the volume of the sea.History, Form & Aesthetic
Improving Data Availability in Decentralized Storage Systems
No full textPhD thesis in Information technologyPreserving knowledge for future generations has been a primary concern for humanity since the dawn of civilization. State-of-the-art methods have included stone carvings, papyrus scrolls, and paper books. With each advance in technology, it has become easier to record knowledge. In the current digital age, humanity may preserve enormous amounts of knowledge on hard drives with the click of a button.
The aggregation of several hard drives into a computer forms the basis for a storage system. Traditionally, large storage systems have comprised many distinct computers operated by a single administrative entity.
With the rise in popularity of blockchain and cryptocurrencies, a new type of storage system has emerged. This new type of storage system is fully decentralized and comprises a network of untrusted peers cooperating to act as a single storage system. During upload, files are split into chunks and distributed across a network of peers. These storage systems encode files using Merkle trees, a hierarchical data structure that provides integrity verification and lookup services.
While decentralized storage systems are popular and have a user base in the millions, many technical aspects are still in their infancy. As such, they have yet to prove themselves viable alternatives to traditional centralized storage systems.
In this thesis, we contribute to the technical aspects of decentralized storage systems by proposing novel techniques and protocols. We make significant contributions with the design of three practical protocols that each improve data availability in different ways.
Our first contribution is Snarl and entangled Merkle trees. Entangled Merkle trees are resilient data structures that decrease the impact hierarchical dependencies have on data availability. Whenever a chunk loss is detected, Snarl uses the entangled Merkle trees to find parity chunks to repair the lost chunk. Our results show that by encoding data as an entangled Merkle tree and using Snarl’s repair algorithm, the storage utilization in current systems could be improved by over five times, with improved data availability.
Second, we propose SNIPS, a protocol that efficiently synchronizes the data stored on peers to ensure that all peers have the same data. We designed a Proof of Storage-like construction using a Minimal Perfect Hash Function. Each peer uses the PoS-like construction to create a storage proof for those chunks it wants to synchronize. Peers exchange storage proofs and use them to efficiently determine which chunks they are missing. The evaluation shows that by using SNIPS, the amount of synchronization data can be reduced by three orders of magnitude in current systems.
Lastly, in our third contribution, we propose SUP, a protocol that uses cryptographic proofs to check if a chunk is already stored in the network before doing wasteful uploads. We show that SUP may reduce the amount of data transferred by up to 94 % in current systems.
The protocols may be deployed independently or in combination to create a decentralized storage system that is more robust to major outages. Each of the protocols has been implemented and evaluated on a large cluster of 1,000 peers
A Privacy-Preserving and Transparent Certification System for Digital Credentials
No full textA certification system is responsible for issuing digital credentials, which attest claims about a subject, e.g., an academic diploma. Such credentials are valuable for individuals and society, and widespread adoption requires a trusted certification system. Trust can be gained by being transparent when issuing and verifying digital credentials. However, there is a fundamental tradeoff between privacy and transparency. For instance, admitting a student to an academic program must preserve the student’s privacy, i.e., the student’s grades must not be revealed to unauthorized parties. At the same time, other applicants may demand transparency to ensure fairness in the admission process. Thus, building a certification system with the right balance between privacy and transparency is challenging.
This paper proposes a novel design for a certification system that provides sufficient transparency and preserves privacy through selective disclosure of claims such that authorized parties can verify them. Moreover, unauthorized parties can also verify the correctness of the certification process without compromising privacy. We achieve this using an incremental Merkle tree of cryptographic commitments to users' credentials. The commitments are added to the tree based on verifying zero-knowledge issuance proofs. Users store credentials off-chain and can prove the ownership and authenticity of credentials without revealing their commitments. Further, our approach enables users to prove statements about the credential’s claims in zero-knowledge. Our design offers a cost-efficient solution, reducing the amount of linkable on-chain data by up to 79% per credential compared to prior work, while maintaining transparency
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