15665141
An incremental genetic algorithm approach to multiprocessor scheduling
We have developed a genetic algorithm (GA) approach to the problem of task scheduling for multiprocessor systems. Our approach requires minimal problem specific information and no problem specific operators or repair mechanisms. Key features of our system include a flexible, adaptive problem representation and an incremental fitness function. Comparison with traditional scheduling methods indicates that the GA is competitive in terms of solution quality if it has sufficient resources to perform its search. Studies in a nonstationary environment show the GA is able to automatically adapt to changing targets.
16013631
Populating Genomes in a Dynamic Grid
We study the behavior of a spatially distributed GA (Collins and Jefferson 1991) that has several unique features. First, individuals are allowed to move within a two dimensional grid over time. Such movement results in a continual change in the local environment in which each individual interacts. Second, selection is directly based on an individual’s energy value and indirectly based on fitness. The fitness of an individual determines its initial energy level, but an individual’s energy level at any point during a run reflects a combination of its fitness and its interactions in the environment. Third, the population size can change dynamically throughout a run.
10203274
Adaptation of Length in a Nonstationary Environment
In this paper, we examine the behavior of a variable length GA in a nonstationary problem environment. Results indicate that a variable length GA is better able to adapt to changes than a fixed length GA. Closer examination of the evolutionary dynamics reveals that a variable length GA can in fact take advantage of its variable length representation to exploit good quality building blocks after a change in the problem environment.
5492949
Resource Matching and a Matchmaking Service for an Intelligent Grid
We discuss the application of matching in the area of resource discovery and resource allocation in grid computing. We present a formal definition of matchmaking, overview algorithms to evaluate different matchmaking expressions, and develop a matchmaking service for an intelligent grid environment. Keywords—Grid, Matchmaking, Ontology
28810285
Workflow management and resource discovery for an intelligent grid
A computational grid provides coordinated and transparent access to computing resources for grid users. Workflow management and resource discovery are two important functions of an intelligent grid. Workflow management refers to automatic workflow creation and coordinated workflow execution, and resource discovery facilitates resource allocation and claiming. In this paper we discuss workflow management and resource discovery in an intelligent grid environment.
18463797
Planning with Recursive Subgoals
In this paper, we introduce an effective strategy for subgoal division and ordering based upon recursive subgoals and combine this strategy with a genetic-based planning approach. This strategy can be applied to domains with conjunctive goals. The main idea is to recursively decompose a goal into a set of serializable subgoals and to specify a strict ordering among the subgoals. Empirical results show that the recursive subgoal strategy reduces the size of the search space and improves the quality of solutions to planning problems.
120152362
Graph matching using spectral embedding and alignment
This paper describes how graph-spectral methods can be used to transform the node correspondence problem into one of point-set alignment. We commence by using the ISOMAP algorithm to embed the nodes of a graph in a low-dimensional Euclidean space. With the nodes in the graph transformed to points in a metric space, we can recast the problem of graph matching into that of aligning the points. Here, we use a variant of the Scott and Longuet-Higgins algorithm to find point correspondences. We experiment with the resulting algorithm on a number of real-world problems.
26402360
Signed quorum systems
With n servers that independently fail with probability of p < 0.5, it is well known that the majority quorum system achieves the best availability among all quorum systems. However, even this optimal construction requires (n+1)/2 functioning servers out of n. Furthermore, the number of probes needed to acquire a quorum is also lower bounded by (n+1)/2.Motivated by the need for a highly available and low probe complexity quorum system in the Internet, this paper proposes signed quorum systems (SQS) that can be available as long as any O(1) servers are available, and simultaneously have O(1) probe complexity. SQS provides probabilistic intersection guarantees and exploits the property of independent mismatches in today’s Internet. Such key property has been validated previously under multiple Internet measurement traces. This paper then extensively studies the availability, probe complexity, and load of SQS, derives lower bounds for all three metrics, and constructs matching upper bounds. We show that in addition to the qualitatively superior availability and probe complexity, SQS also decouples availability from load and probe complexity, so that optimal availability can be achieved under most probe complexity and load values.
2617895
Overcoming the Majority Barrier in Large-Scale Systems
In asynchronous environments, the majority barrier prevents us from achieving consensus when more than half of the nodes fail. We argue that the majority barrier significantly limits the availability of practical systems such as peer-to-peer systems. To overcome the barrier realistically, this paper proposes a witness model that probabilistically strengthens the traditional asynchronous model for large-scale systems. The model is motivated by the prevalence of fuzzy partitions in today’s Internet, namely, reachability is far from transitive. Our assumptions in the model are strictly weaker than those in previous approaches. To show that the model is realistic, we carefully use real Internet measurements to validate our strengthening assumptions. On the other hand, we design three consensus protocols under the witness model that can tolerate n-1 failures, showing that the model is strong enough to overcome the majority barrier.
7603120
Defragmenting DHT-based Distributed File Systems
Existing DHT-based file systems use consistent hashing to assign file blocks to random machines. As a result, a user task accessing an entire file or multiple files needs to retrieve blocks from many different machines. This paper demonstrates that significant availability and performance gains can be achieved if instead, users are able to retrieve all the data needed for a given task from only a few DHT nodes. We explore the design and implications of such a "defragmented" DHT-based distributed file system, called D2, that also maintains important DHT properties like storage load balance. We show using real-world file system traces that a simple key encoding scheme is sufficient to maintain good defragmentation for most user tasks. Using both simulation and an actual 1,000 node deployment, we show that D2 increases availability by over an order of magnitude and improves user-perceived latency by 30- 100% compared to a traditional design.
5638908
Invalidation Clues for Database Scalability Services
For their scalability needs, data-intensive Web applications can use a database scalability service (DBSS), which caches applications' query results and answers queries on their behalf. One way for applications to address their security/privacy concerns when using a DBSS is to encrypt all data that passes through the DBSS. Doing so, however, causes the DBSS to invalidate large regions of its cache when data updates occur. To invalidate more precisely, the DBSS needs help in order to know which results to invalidate; such help inevitably reveals some properties about the data. In this paper, we present invalidation clues, a general technique that enables applications to reveal little data to the DBSS, yet limit the number of unnecessary invalidations. Compared with previous approaches, invalidation clues provide applications significantly improved tradeoffs between security/privacy and scalability. Our experiments using three Web application benchmarks, on a prototype DBSS we have built, confirm that invalidation clues are indeed a low-overhead, effective, and general technique for applications to balance their privacy and scalability needs.