wiley interscience tools and environments for parallel and distributed computing phần 8 potx

Moreover, although we are able to define theterm Grid approach, we need to recognize that, similar to the gestalt approach in psychology, we face different responses by the community to t

part of the overhead Second, the DCOM implementation uses the concept of

moniker for obtaining object reference This is achieved by converting the moniker into a string and writing the string into a moniker file, which could

later be read by the client program to obtain the reference

In the case of matrix-by-vector multiplication, the client passes the matrixand vector objects by references to the central server The central server then

looks up the available processor objects by reading the moniker file

corre-sponding to the processor object and then performs the computation This

reading of the moniker file is an I/O activity, which very much stands as

ratio-COMPARISON OF THE THREE PARADIGMS 145 Table 4.4 Comparison Based on Support for Additional Features

Enforces the creation of The CORBA Security DCOM supports robust

a RMISecurityManager Service supports the security by allowing object This ensures that identification, users to specify user- downloaded class code authentication, level authentication and for any object passed authorization, and access-level rights

to the client does not access control of the (through access control access the system principles It also list) over objects.

auditing.

Distributed garbage Distributed garbage Distributed garbage collection is handled by collection is not collection is activated by

detects whether clients are connected.

Asynchronous call-back Deferred synchronous Call-back interfaces are routines are supported calls allow clients to supported in DCOM where in a server can poll on a delayed

call back a method on response from the

any of its clients server Event service

allows consumers to either request events or

be notified of events.

TABLE 4.5 Comparison Based on Performance

Matrix-by-vector By reference 6781.155 1546.716 123,305.330 multiplication

nale for the slow performance of DCOM in the matrix-by-vector

multiplica-tion experiment However, in the ping experiment, as the moniker file was read

before the object was passed-by-value, the result shows a reasonably lowercomputation time

4.5 CONCLUSIONS

As evident from Section 4.4, each model has strengths and weaknesses Eachperforms better under some conditions, while the performance degrades insome other situations Hence the question “Which approach is better?” doesnot have a unique answer Instead, the open nature of the future distributedsystems will need the creation of a comprehensive metaobject model, whichwill seamlessly encompass the objects adhering to different models, therebypromoting a conglomeration of heterogeneous objects UMM (the UnifiedMeta-object Model) [25] is one such proposed metamodel being developedfor providing solutions to the software development of future open systems.UMM is based on an amalgamation of three concepts: objects, service, and col-laboration More details about UMM are available in [25]

11 K Brockschmidt, Inside OLe (Microsoft Programming), Microsoft Press,

16 R Orfali and D Harkey, Client/Server Programming with JAVA and CORBA,

Wiley, New York, 1998.

17 K Keahey, A brief tutorial on Corba,

21 CORBA basics, http://ootips.org/corba-basics.html.

22 Microsoft Corporation, http://www.microsoft.com/java.

23 Linar Ltd., J-Integra, pure Java–COM bridge, www.linar.com.

24 G S Raj, A detailed comparison of CORBA, DCOM and Java/RMI,

http://www.execpc.com/~gopalan/misc/compare.html.

25 R R Raje, UMM: unified meta-object model for open distributed systems, ceedings of the 4th IEEE International Conference on Algorithms and Architecture for Parallel Processing, Word Scientific Publishing Company, Singapore, 2000.

Pro-26 J-Integra, http://j-integra.intrinsyc.com.

REFERENCES 147

Argonne National Laboratory, Argonne, IL

and Illinois Institute of Technology, Chicago, IL

5.1 INTRODUCTION

The Grid approach is an important development in the discipline of computer

science and engineering Rapid progress is being made on several levels,including the definition of terminology, the design of an architecture andframework, the application in the scientific problem-solving process, and thecreation of physical instantiations of Grids on a production level In thischapter we provide an overview of important influences, developments, andtechnologies that are shaping state-of-the-art Grid computing In particular,

we address the following questions:

• What motivates the Grid approach? (see Section 5.1.1)

• What is the architecture of a Grid? (see Section 5.3)

• Which Grid research activities are performed? (see Section 5.5)

• How do researchers use a Grid? (see Section 5.7.7)

• What will the future bring? (see Section 5.8)Before we begin our discussion, we start with an observation that leads us

to the title of this chapter A strong overlap between past, current, and futureresearch in other disciplines influences this new area and makes answers to

149

Tools and Environments for Parallel and Distributed Computing, Edited by Salim Hariri

and Manish Parashar

ISBN 0-471-33288-7 Copyright © 2004 John Wiley & Sons, Inc.

some of the questions complex Moreover, although we are able to define the

term Grid approach, we need to recognize that, similar to the gestalt approach

in psychology, we face different responses by the community to this evolvingfield of research Based on the gestalt approach, which hypothesizes that aperson’s perception of stimuli has an effect on his response, we will see avariety of stimuli on the Grid approach that influence current and futureresearch directions

We close this introductory section with a famous pictureused in early psychology experiments If we examine thedrawing in detail, it will be rather difficult to decide whatthe different components represent in each of the inter-pretations Although hat, feather, and ear are identifiable

in the figure, one’s interpretation (Is it an old woman or ayoung girl?) is based instead on “perceptual evidence.”This figure should remind us to be open to individual per-ceptions about Grids and to be aware of the multifaceted

aspects that constitute the gestalt of the Grid.

5.1.1 Motivation

To define the term Grid we first identify what motivates its development We

provide an example from weather forecasting and modeling that includes auser community with strong influence on the newest trends of computerscience over the past several decades L F Richardson [68,72] expressed thefirst modern vision of numerical weather prediction in 1922 Within twodecades, the first prototype of a prediction system had been implemented byvon Neumann, Charney, and others on the first generation of computers [70].With the increased power of computers, numerical weather prediction became

a reality in the 1960s and initiated a revolution in the field that we are stillexperiencing In contrast to these early weather prediction models, today thescientific community understands that complex chemical processes and theirinteractions with land, sea, and atmosphere have to be considered

Several factors make this effort challenging Massive amounts of data must

be gathered worldwide; those data must be incorporated into sophisticatedmodels; the results must be analyzed; feedback must be provided to the mod-elers; and predictions must be supplied to consumers (Figure 5.1)

Analyzing this process further, we observe that the data needed as input

to the models based on observations and measurements of weather andclimate variables are still incomplete, and sophisticated sensor networks must be put in place to improve this situation The complexity of these systemshas reached a level where it is no longer possible for a single scientist tomanage the entire process; the era of the lonely scientist working in seclusion

is coming to an end Today, accurate weather models are derived by sharing the intellectual property within a community of interdisciplinaryresearchers

This increase in the complexity on the numerical methods and amount ofdata required, along with the factor of community access, requires access

to massive amounts of computational and storage resources Although today’ssupercomputers offer enormous power, accurate climate and weather modeling requires access to even larger resources that may be integrated from resources at dispersed locations Therefore, weather prediction promotesmore than just a focus on making compute resources available as part of a networked environment We have identified the need for an infrastructure to

be created from a dynamic, dispersed set of sensor, data, compute, tion, and delivery networks Clearly, weather forecasting is a complex processthat requires flexible, secure, coordinated sharing of a wide variety ofresources

calculate collaborate

Fig 5.1 Weather forecasting is a complex process that requires a complex infrastructure.

experts to believe that the network speed doubles every nine months At thesame time, the cost of production for network and computer hardware isdecreasing.

We also observe a change in modality of computer operation The first

gen-eration of supercomputers comprised high-end mainframes, vector processors,and parallel computers Access to this expensive infrastructure was providedand controlled as part of a single institution within a single administrativedomain With the advent of network technologies, promoting connectivitybetween computers, and the creation of the Internet, promoting connectivitybetween different organizations, a new trend arose, leading away from the cen-tralized computing center to a decentralized environment As part of thistrend, it was natural to collect geographically dispersed and possibly hetero-geneous computer resources, typically as networks of workstations or super-computers The first connections between high-end computers used to solve a

problem in parallel on these machines were termed a metacomputer (The term

is believed to have originated as part of a gigabit testbed [60].)

Thus, increases in capacity, capability, and modality are enabling a new way

of doing distributed science Additionally, technology once viewed as

special-ized infrastructure is becoming a commodity technology, making it possible toaccess resources, for example through the use of the Internet [68], more easily.This vision, which has become clearer over the past few decades, now applies

to many other disciplines that will provide commercial viability in the nearfuture It has had, and will continue to have, a profound impact on several scientific disciplines, including computer science

5.2 DEFINITIONS

In this section we provide the most elementary definition of the term Grid and

its use within the community As we have seen, the Grid approach has beenguided by a complex and diverse set of requirements but at the same time pro-vides us with a vision for an infrastructure that promotes sophisticated inter-national scientific and business-oriented collaborations Much research in thisarea, some of which is mentioned in this chapter, has been influential in

shaping what we now term the Grid approach:

Definition: Grid Approach A strategy that promotes a vision for cated international scientific and business-oriented collaborations

sophisti-The term Grid is an analogy to the electric power grid that allows

perva-sive access to electric power In a similar fashion, computational Grids provideaccess to collections of compute-related resources and services As early as

1965, the designers of the Multics operating system envisioned and namedrequirements for a computer facility operating “like a power company or

water company” [80], and others envisioned Grid-like scenarios [59] However,

we emphasize that our current understanding of the Grid approach goes farbeyond simply sharing compute resources in a distributed fashion Besidessupercomputer and compute pools, Grids include access to informationresources (such as large-scale databases) and access to knowledge resources(such as collaborative interactions between colleagues) Essential is that theseresources may be at geographically dispersed locations and may be controlled

by different organizations Thus, the following definition for a Grid is appropriate:

Definition: Grid An infrastructure that allows for flexible, secure, nated resource sharing among dynamic collections of individuals, resources,and organizations

coordi-So far we have used the term Grid rather abstract manner To distinguish

the concept of a Grid from an actual instantiation of a Grid as a real,

avail-able infrastructure, we use the term production Grid Such production Grids

are typically shared among a set of users The analogy in the electrical powerGrid would be a power company or agglomerate of companies that maintaintheir own Grid while providing persistent services to the user community.Thus, the following definition is introduced:

Definition: Production Grid An instantiaion of a Grid that manifests itself

by including a set of resources to be accessed by Grid users

Additionally, we expect that multiple production Grids will exist and be supported by multiple organizations Fundamental to the Grid is the idea

of sharing Naturally, it should be possible to connect such Grids with each

other so as to share resources Thus, it is important to define a set of mentary standards that assist to provide interoperability between productionGrids

ele-Some production Grids are created based on the need to support a ular community Although the resources within such a community are usuallycontrolled in different administrative domains, they can be accessed as part of

partic-a community production Grid Expartic-amples of production partic-and community

pro-duction Grids are introduced in Section 5.5.1

Definition: Community Production Grid A production Grid in which ation and maintenance are performed by a community of users, developers,and administrators

cre-The management of a community production Grid is usually handled by a

virtual organization [46], which defines the rules that guide membership and

use of resources

DEFINITIONS 153

Definition: Virtual Organization An organization that defines rules thatguide membership and use of individuals, resources, and institutions within acommunity production Grid.

A typical Grid will contain a number of high-end resources such as computers or data storage facilities As these resources can be consumed byusers, we term them in analogy to electrical power plants as follows:

super-Definition: Grid Plane A high-end resource that is integrated in a virtualorganization and can be shared by its users

The user, on the other hand, is able to access these resources through a specific device such as a computer, handheld device, or cell phone

user-Definition: Grid Appliance A device that can be integrated into a Grid whileproviding the user with a service that uses resources accessible through the Grid.Grid appliances provide a portal that enables easy access, utilization, andcontrol of resources available through a Grid by the user We define the term

Grid portal in more detail in Section 5.7.

One important concept that was originally not sufficiently addressed withinthe Grid community was the acknowledgment of sporadic and ad hoc Gridsthat promote the creation of time-limited services This concept was first for-mulated as part of an initial Grid application to conduct structural biology andcomputed microtomography experiments at Argonne National Laboratory’sAdvanced Photon Source (APS) In these applications, it was not possible toinstall, on long-term basis, Grid-related middleware on the resources, because

of policy and security considerations Hence, besides the provision for a vasive infrastructure, we require Grid middleware to enable sporadic and adhoc Grids that provide services with limited lifetime Furthermore, the admin-istrative overhead of installing such services must be small, to allow the instal-lation and maintenance to be conducted by the nonexpert with few systemprivileges

per-5.3 MULTIFACETED GRID ARCHITECTURE

A review of the literature about existing Grid research projects shows thatthree different architectural representations are commonly used Each ofthese architectural views attempts to present a particular aspect of Grids Thus,

we believe it is important recognize that the architecture of the Grid is multifaceted and an architectural abstraction should be chosen that fits best

to describe the given aspect of the Grid research Nevertheless, in each caseone needs to consider the distributed nature and unique security aspects Next

we describe these common architectural views in more detail

5.3.1 N-Tiered Grid Architecture

The N-tiered application architecture (Figure 5.2) provides a model for Grid

developers to create flexible and reusable Grid applications Decomposing aGrid application into tiers allows developers to modify or add only to a spe-cific layer rather than to focus on the reimplementation of all parts of the

application N-tiered application architectures are common within and are

most often represented as part of layer 7 of the OSI model [64] Many

Grid projects provide an N-tiered architecture The advantage of an N-tiered

architecture is its familiarity and its applicability to many conceptual Gridproblems that try to separate issues between the application and the physicallayer

5.3.2 Role-Based Grid Architecture

The secure access to a collectively controlled set of physical resources reused

by applications motivates a role-based layered architecture [46,47] Within thisarchitecture, it is easy to identify fundamental system components, specify thepurpose and function of these components, and indicate how these compo-nents interact with one another This architecture classifies protocols, services,application programming interfaces, and software development kits according

to their roles in enabling resource sharing It identifies five layers: fabric,connectivity, resource, collective, and application layer (Figure 5.3) Inter-operability is preserved by using a small standard set of protocols assisting inthe secure exchange of information and data among single resources Theseresources are managed by collective services in order provide the illusion of

a single resource to application designers and users

The layers within the architecture are defined as follows:

• The fabric layer contains protocols, application interfaces, and toolkits

that allow development of services and components to access locally trolled resources, such as computers, storage resources, networks, andsensors

con-MULTIFACETED GRID ARCHITECTURE 155

Grid

Advanced

Fig 5.2 N-tiered Grid architecture based on an application user’s point of view.