[Show abstract][Hide abstract] ABSTRACT: Stream grids are wide-area grid computing environments that are fed by a set of stream data sources, and Queries arrive at the grid from users and applications external to the system. The kind of queries considered in this work is long-running continuous LRC queries, which are neither short-lived nor infinitely long lived. The queries are "open" from the grid perspective as the grid cannot control or predict the arrival of a query with time, location, required data and query revocations. Query optimization in such an environment has two major challenges, i.e., optimizing in a multi-query environment and continuous optimization, due to new query arrivals and revocations. As generating a globally optimal query plan is an intractable problem, this work explores the idea of emergent optimization where globally optimal query plans emerge as a result of local autonomous decisions taken by the grid nodes. Drawing concepts from evolutionary game theory, grid nodes are modeled as autonomous agents that seek to maximize a self-interest function using one of a set of different strategies. Grid nodes change strategies in response to variations in query arrival and revocation patterns, which is also autonomously decided by each grid node.
[Show abstract][Hide abstract] ABSTRACT: Stream grids are wide-area grid computing environments that are fed by a set of stream data sources. Such grids are becoming more wide-spread due to the large scale deployment of sensor networks for a wide range of applications, from monitoring geophysical activities to supply chain management coupled with applications like network monitoring. Queries external to the system arrive on any node in the grid seeking data from one or more data streams. The kind of queries considered in this work are (1) lifetime queries and (2) long running queries where new query arrivals and query revocations are infrequent. From the system perspective, computing the optimal query plan for the set of queries incident on the grid would ensure minimal system-wide resource usage, thereby maximizing the number of concurrent queries that can be supported. The key challenge in such a system is multi-query optimization. In this work, we analyze the complexity of multi-query optimization for select, project and join queries in isolation and propose algorithms for computing optimal query plans if polynomial time algorithms exist. 1
[Show abstract][Hide abstract] ABSTRACT: The role of a distributed index from the perspective of an individual actor (node) is to minimize its separation from all other actors (nodes). From a systemwide perspective, an optimal distributed index is one that minimizes the diameter of the index graph. We tackle this optimization problem in an evolutionary fashion by performing a series of topology crossovers and fitness-based selections. A set of constraints regulate the fitness function. Different classes of topologies such as star, circle, and skip lists emerge as diameter-optimal structures under different constraints. Knowledge of the optimal topology class in a given context provides strategic information for distributed agents to (re)construct a global index structure based on local information. We also investigate a deterministic approach called polygon embedding, to build topologies with similar properties to that of the evolved topologies.
[Show abstract][Hide abstract] ABSTRACT: Multi-stream interactive systems can be seen as \hidden adversary" systems (HAS), where the observable behaviour on any interaction channel is afiected by interactions happening on other channels. One way of modelling HAS is in the form of a multi-process I/O automata, where each interacting process appears as a token in a shared state space. Constraints in the state space specify how the dynamics of one process afiects other processes. We deflne the \liveness criterion" of each process as the end objective to be achieved by the process. The problem now for each process is to achieve this objective in the face of unforeseen interferences from other processes. In an earlier paper, it was proposed that this uncertainty can be mitigated by collaboration among the disparate processes. Two types of collaboration philosophies were also suggested: altruistic collaboration and pragmatic collaboration. This paper addresses the HAS validation problem where processes collaborate altruistically.
Full-text · Article · May 2008 · Electronic Notes in Theoretical Computer Science
[Show abstract][Hide abstract] ABSTRACT: WAND is a P2P meta-data management system providing a file-system tree interface. Users are able to share files on the global
file-system tree. The file system tree is robust and maintains its structure even when nodes enter and leave the network.
The key ideas that make the file-system tree robust are a concept of virtual folders and a novel algorithm to handle network partitioning.
[Show abstract][Hide abstract] ABSTRACT: Query optimization in sensor grids have two major challenges: (a) optimizing in a multi-query environment, and (b) continuous re-optimization occurring due to new query registrations and de-queries, i.e. queries being stopped unexpectedly. Addressing this problem continuously on a system-wide basis is an infeasible option. In this work called EstuaryDB, we propose a notion of emergent optimization, where globally optimal configurations emerge as a result of a number of local autonomous decisions carried out in self-interest. Grid nodes act as self-interested autonomous agents that continuously seek to maximize their "wealth." The agents are unaware of system-wide issues such as when do queries arrive, what are they asking for, or when are they revoked. Every query brings with it a certain amount of wealth, and each agent continuously tries to save as much of the wealth as possible. The amount of latent wealth in the system at any time gives a quantitative measure of the efficiency achieved over naive stream retrieval.
[Show abstract][Hide abstract] ABSTRACT: Large information systems (IS) comprise of several independent applications that share a common set of resources and data. Usually, there are implicit and subtle dependencies across these applications that are not specifically captured. This is especially so if the applications are bought off the shelf or are developed by independent third parties. Dependencies or global semantic constraints are difficult to discern and incorporate into the design of individual software components. Global constraints may change over time and it is usually expensive or infeasible to change individual application logic in every such situation. In order to address such an issue, we propose LogicFence, a framework that accepts a definition of global constraints and translates these constraints into primitives that are embedded into the run-time environments of application programs (currently, into the JVM of Java applications). LogicFence monitors the state of application programs and prevents the disparate instances to collectively form a globally inconsistent state
[Show abstract][Hide abstract] ABSTRACT: A new architecture for scheduling an open-ended set of medical post processing applications in clusters is described in this work. The scheduler takes into consideration the characteristics of the set of currently executing applications as well as the incoming request to ensure optimal application performance. The approach uses a feedback mechanism to learn the resource requirements of an application and is non-intrusive. The scheduler is not tightly coupled with the applications and therefore can schedule an open-ended set of applications.
[Show abstract][Hide abstract] ABSTRACT: WAND is a meta-data management system that provides a file-system tree for users of an internet based P2P network. The tree is robust and retains its structure even when nodes (peers) enter and leave the network. The robustness is based on a concept of virtual folders that are automatically created to retain paths to lower level folders whenever a node hosting a higher-level folder moves away. Other contributions of the WAND system include its novel approach towards managing root directory information and handling network partitions.