49,917 research outputs found
A metaobject architecture for fault-tolerant distributed systems : the FRIENDS approach
The FRIENDS system developed at LAAS-CNRS is a metalevel architecture providing libraries of metaobjects for fault
tolerance, secure communication, and group-based distributed applications. The use of metaobjects provides a nice separation of concerns between mechanisms and applications. Metaobjects can be used transparently by applications and can be composed according to the needs of a given application, a given architecture, and its underlying properties. In FRIENDS, metaobjects are used recursively to add new properties to applications. They are designed using an object oriented design method and implemented on top of basic system services. This paper describes the FRIENDS software-based architecture, the object-oriented development of metaobjects, the experiments that we have done, and summarizes the advantages and drawbacks of a metaobject approach for building fault-tolerant system
A smart end-effector for assembly of space truss structures
A unique facility, the Automated Structures Research Laboratory, is being used to investigate robotic assembly of truss structures. A special-purpose end-effector is used to assemble structural elements into an eight meter diameter structure. To expand the capabilities of the facility to include construction of structures with curved surfaces from straight structural elements of different lengths, a new end-effector has been designed and fabricated. This end-effector contains an integrated microprocessor to monitor actuator operations through sensor feedback. This paper provides an overview of the automated assembly tasks required by this end-effector and a description of the new end-effector's hardware and control software
Middleware-based Database Replication: The Gaps between Theory and Practice
The need for high availability and performance in data management systems has
been fueling a long running interest in database replication from both academia
and industry. However, academic groups often attack replication problems in
isolation, overlooking the need for completeness in their solutions, while
commercial teams take a holistic approach that often misses opportunities for
fundamental innovation. This has created over time a gap between academic
research and industrial practice.
This paper aims to characterize the gap along three axes: performance,
availability, and administration. We build on our own experience developing and
deploying replication systems in commercial and academic settings, as well as
on a large body of prior related work. We sift through representative examples
from the last decade of open-source, academic, and commercial database
replication systems and combine this material with case studies from real
systems deployed at Fortune 500 customers. We propose two agendas, one for
academic research and one for industrial R&D, which we believe can bridge the
gap within 5-10 years. This way, we hope to both motivate and help researchers
in making the theory and practice of middleware-based database replication more
relevant to each other.Comment: 14 pages. Appears in Proc. ACM SIGMOD International Conference on
Management of Data, Vancouver, Canada, June 200
Evolving NoSQL Databases Without Downtime
NoSQL databases like Redis, Cassandra, and MongoDB are increasingly popular
because they are flexible, lightweight, and easy to work with. Applications
that use these databases will evolve over time, sometimes necessitating (or
preferring) a change to the format or organization of the data. The problem we
address in this paper is: How can we support the evolution of high-availability
applications and their NoSQL data online, without excessive delays or
interruptions, even in the presence of backward-incompatible data format
changes?
We present KVolve, an extension to the popular Redis NoSQL database, as a
solution to this problem. KVolve permits a developer to submit an upgrade
specification that defines how to transform existing data to the newest
version. This transformation is applied lazily as applications interact with
the database, thus avoiding long pause times. We demonstrate that KVolve is
expressive enough to support substantial practical updates, including format
changes to RedisFS, a Redis-backed file system, while imposing essentially no
overhead in general use and minimal pause times during updates.Comment: Update to writing/structur
A database management capability for Ada
The data requirements of mission critical defense systems have been increasing dramatically. Command and control, intelligence, logistics, and even weapons systems are being required to integrate, process, and share ever increasing volumes of information. To meet this need, systems are now being specified that incorporate data base management subsystems for handling storage and retrieval of information. It is expected that a large number of the next generation of mission critical systems will contain embedded data base management systems. Since the use of Ada has been mandated for most of these systems, it is important to address the issues of providing data base management capabilities that can be closely coupled with Ada. A comprehensive distributed data base management project has been investigated. The key deliverables of this project are three closely related prototype systems implemented in Ada. These three systems are discussed
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