Design of efficient and elastic storage in the cloud

Ph.DDOCTOR OF PHILOSOPH

Study of fault-tolerant software technology

Presented is an overview of the current state of the art of fault-tolerant software and an analysis of quantitative techniques and models developed to assess its impact. It examines research efforts as well as experience gained from commercial application of these techniques. The paper also addresses the computer architecture and design implications on hardware, operating systems and programming languages (including Ada) of using fault-tolerant software in real-time aerospace applications. It concludes that fault-tolerant software has progressed beyond the pure research state. The paper also finds that, although not perfectly matched, newer architectural and language capabilities provide many of the notations and functions needed to effectively and efficiently implement software fault-tolerance

Atomic Broadcast in Heterogeneous Distributed Systems

Communication services have long been recognized as possessing a dominant effect on both performance and robustness of distributed systems. Distributed applications rely on a multitude of protocols for the support of these services. Of crucial importance are multicast protocols. Reliable multicast protocols enhance the efficiency and robustness of distributed systems. Numerous reliable multicast protocols have been proposed, each differing in the set of assumptions adopted, especially for the communication network. These assumptions make each protocol suitable for a specific environment. The presence of different distributed applications that run on different LANs and single distributed applications that span different LANs mandate interaction between protocols on these LANs. This interaction is driven by the necessity of cooperation between individual applications. The state of the art in reliable multicast protocols renders itself inadequate for multicasting in interconnected LANs. The progress in development methodology for efficient and robust LAN software has not been matched by similar advances for WANs. A high-latency, a lower bandwidth, a higher probability of partitions, and a frequent loss of messages are the main restrictive barriers. In our work, we propose a global standard protocol that orchestrates cooperation between the different reliable broadcast protocols that run on different LANs. Our objective is to support a reliable ordered delivery service for inter-LAN messages and achieve the utmost utilization of the underlying local communication services. Our protocol suite accommodates the existence of LANs managed by autonomous authorities. To uphold this autonomy (as a defacto condition), LANs under different authorities must be able to adopt different ordering criteria for group multicasting. The developed suite assumes an environment in which multicasting groups can have members that belong to different LANs; each group can adopt either total or causal order for message delivery to its members. We also recognize the need for interaction between different reliable multicasting protocols. This interaction is a necessity in an autonomous environment in which each local authority selects a protocol that is suitable to its individual needs. Our protocols are capable of interacting with any reliable protocol that achieves a causal order as well as with all timestamp-based total-order protocols. Our protocols can also be used as a medium for interaction between existing reliable multicasting protocols. This feature opens new avenues in interactability between reliable multicasting protocols. Finally, our protocol suite enjoys a communication structure that can be aligned with the actual routing topology, which largely minimizes the necessary protocol messages

Proceedings Work-In-Progress Session of the 13th Real-Time and Embedded Technology and Applications Symposium

The Work-In-Progress session of the 13th IEEE Real-Time and Embedded Technology and Applications Symposium (RTAS\u2707) presents papers describing contributions both to state of the art and state of the practice in the broad field of real-time and embedded systems. The 17 accepted papers were selected from 19 submissions. This proceedings is also available as Washington University in St. Louis Technical Report WUCSE-2007-17, at http://www.cse.seas.wustl.edu/Research/FileDownload.asp?733. Special thanks go to the General Chairs – Steve Goddard and Steve Liu and Program Chairs - Scott Brandt and Frank Mueller for their support and guidance

Attribute-Level Versioning: A Relational Mechanism for Version Storage and Retrieval

Data analysts today have at their disposal a seemingly endless supply of data and repositories hence, datasets from which to draw. New datasets become available daily thus making the choice of which dataset to use difficult. Furthermore, traditional data analysis has been conducted using structured data repositories such as relational database management systems (RDBMS). These systems, by their nature and design, prohibit duplication for indexed collections forcing analysts to choose one value for each of the available attributes for an item in the collection. Often analysts discover two or more datasets with information about the same entity. When combining this data and transforming it into a form that is usable in an RDBMS, analysts are forced to deconflict the collisions and choose a single value for each duplicated attribute containing differing values. This deconfliction is the source of a considerable amount of guesswork and speculation on the part of the analyst in the absence of professional intuition. One must consider what is lost by discarding those alternative values. Are there relationships between the conflicting datasets that have meaning? Is each dataset presenting a different and valid view of the entity or are the alternate values erroneous? If so, which values are erroneous? Is there a historical significance of the variances? The analysis of modern datasets requires the use of specialized algorithms and storage and retrieval mechanisms to identify, deconflict, and assimilate variances of attributes for each entity encountered. These variances, or versions of attribute values, contribute meaning to the evolution and analysis of the entity and its relationship to other entities. A new, distinct storage and retrieval mechanism will enable analysts to efficiently store, analyze, and retrieve the attribute versions without unnecessary complexity or additional alterations of the original or derived dataset schemas. This paper presents technologies and innovations that assist data analysts in discovering meaning within their data and preserving all of the original data for every entity in the RDBMS