4.2 Analysis Knowledge Management
4.2.5 Knowledge application
Este trabalho apresenta a metodologia e resultados do projeto de pesquisa 468835/2014– 8 do Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) denominado “Uma plataforma distribuída para a modelagem colaborativa, simulação de alto desempenho e
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CacheSIM: A Web Cache Simulator Tool Based on
Coloured Petri Nets and Java Programming
C. G. Furtado Júnior, J. M. Soares and G. C. Barroso Abstract— Efficient policies should be applied in order to
decrease the document retrieval time on distributed systems, the network traffic, admission and content replacement for cache systems. Usually, proposed simulators that aim to select better policies have limitation. As an example, it’s difficult to create scenarios with multiple cache systems. Besides, frequently those simulators present a lack of extensibility resources for both custom policies as to include new mechanisms for measuring performance. To address these issues, we developed CacheSIM. It is an extensible platform for simulating distributed cache systems. Using CacheSIM, we can conceive different scenarios based on a hierarchical Coloured Petri Net (CPN) model. We are able to define one replacement policy of fifteen available and one admission policy of two possible ones. Moreover, we can program custom policies and choose them. This paper presents the architecture and native resources of CacheSIM. We have evaluated its extensibility by including two replacement policies based on semantics found in works of the state of the art. We reproduced scenarios and results of those works, as well as we compared to those obtained using native policies. Thus, we can demonstrate the potential of CacheSIM as a simulation tool.
1Keywords— Coloured Petri Nets, Extensibility, Replacement Policy, Admission Policy, Caches
I. INTRODUÇÃO
AUMENTO expressivo na demanda por serviços e aplicações da Word Wide Web (WWW) gera sobrecarga nos enlaces de comunicação e servidores da Internet [1], percebida sob forma de latência de acesso a documentos.
Web caches são técnicas capazes de reduzir o atraso de acesso e a quantidade de tráfego que é transportado sobre as redes de longa distância, mantendo os documentos próximos aos clientes [2], configurando-se como uma solução eficiente para o problema da latência.
Os Proxies são computadores com capacidade de armazenamento limitada, que se comportam como depósitos de documentos da Web e que disponibilizam um serviço de cache compartilhado com um grupo de usuários, local em que são mantidos os arquivos mais frequentemente acessados. Sempre que o espaço de armazenamento de um proxy está esgotado e é necessário abrigar um novo documento, este deve decidir qual conteúdo será excluído para acomodar um novo. As regras de seleção de documentos para a exclusão são
1C. G. Furtado, Instituto Federal do Ceará (IFCE), Ceará, Brasil, [email protected]
J. M. Soares, Universidade Federal do Ceará (UFC), Ceará, Brasil [email protected]
G. C. Barroso, Universidade Federal do Ceará (UFC), Ceará, Brasil [email protected]
denominadas políticas de substituição.
Outros fatores, como tamanho do documento, distância e largura de banda entre o proxy e o servidor de documentos da Internet, influenciam diretamente no tempo de acesso percebido pelo usuário a um recurso da Web.
Considerando essas restrições, o desenvolvimento de um ambiente de web caches constitui-se em um desafio particular, visto que configurações e políticas precisam ser avaliadas e validadas para diferentes perfis de uso e cenários distintos. Para tanto, duas abordagens de validação são utilizadas [3]: na primeira, funcionalidades do sistema são avaliadas e suas características mensuradas durante o processo de operação em um testbed; na segunda, o comportamento do sistema deve ser reproduzido e avaliado antes de seu efetivo desenvolvimento com o apoio de ferramentas de modelagem e simulação. A primeira situação pode ser inadequada para muitos casos porque o custo de elaboração e configuração de um sistema real é, em geral, elevado, principalmente considerando-se a potencial necessidade de escalabilidade, de configuração e/ou de modificações de módulos implantados em elementos de rede. Entretanto, no segundo caso, com o uso de modelos e simulações, é possível testar e depurar as funcionalidades do sistema antes de seu efetivo desenvolvimento.
Tendo em vista as vantagens das abordagens baseadas em simulação, esse trabalho apresenta o CacheSIM, uma ferramenta baseada no uso de Coloured Petri Nets (CPN) e linguagem de programação Java, cujo objetivo é a disponibilização de uma plataforma para modelagem, configuração e uso de políticas de substituição em cache da WWW. O uso do CacheSIM permite, dentre outras coisas, verificar a eficiência das diversas políticas de admissão e substituição existentes, além de disponibilizar uma interface especial para programação de extensões em Java, o que permite a implementação e a análise de novas políticas de caching. A função de uma política de controle de admissão é decidir se um documento tem de ser armazenado na cache ou não. Tal divisão se dá em virtude da probabilidade de um conteúdo ser referenciado novamente ou do tamanho do documento causar um grande número de exclusões em cache [1].
Ao final de cada simulação, dados estatísticos e gráficos pré-determinados são fornecidos pelo CacheSIM. A interface de extensão pode ser especializada para captura de dados estatísticos particulares e montagens de gráficos personalizados. Para a validação da ferramenta, os cenários discutidos em [4] e [5] foram reproduzidos e os resultados obtidos foram comparados aos dos trabalhos originais. Demonstra-se, assim, o poder de simulação da ferramenta que, além de possibilitar a modelagem e configuração de múltiplos
O
A Petri net-based decision-making framework for assessing cloud
services adoption: The use of spot instances for cost reduction
Maristella Ribas1,a,n, C.G. Furtado2,b, José Neuman de Souza3,c,
Giovanni Cordeiro Barroso4,c, Antão Moura5,d, Alberto S. Lima6,c, Flávio R.C. Sousa7,c aTechne Engenharia e Sistemas, São Paulo, Brazil
bFederal Institute of Ceará (IFCE), Fortaleza, Brazil cFederal University of Ceará, Fortaleza, Brazil
dFederal University of Campina Grande, C. Grande, Brazil
a r t i c l e i n f o
Article history:
Received 20 February 2015 Received in revised form 25 May 2015
Accepted 3 July 2015 Available online 13 July 2015 Keywords: Cloud computing Spot instances BDIM AHP Petri nets a b s t r a c t
Cloud services are widely used nowadays, especially in Infrastructure as a service (IaaS), with vendors offering several purchasing options and expanding the range of services offered on almost a daily basis. Cost reduction is a major factor promoting the adoption of cloud services among enterprises. However, qualitative factors need to be evaluated as well, thus rendering the decision regarding the adoption of cloud services among enterprises a non-trivial task for Information Technology (IT) managers. In this paper, we propose a place/transition or Petri net-based multi-criteria decision-making (MCDM) frame- work to assess a cloud service in comparison with a similar on-premises service. The framework helps IT managers choose between two such options, and can be used for any type of cloud service: Infrastructure as a Service (IaaS), Platform as a service (PaaS), Software as a service (SaaS), etc. Because its low cost is among the most important reasons for adopting cloud services, we also propose a Petri net to model cost savings using the spot instances purchasing option in public clouds. Through simulation of several scenarios, we conclude that spot instances present a very interesting cost-saving option in the auto-scaling process, even for simple business applications using few servers.
&2015 Elsevier Ltd. All rights reserved.
1. Introduction
Cloud computing is defined by the National Institute of Stan- dard and Technology (National Institute of Standards and
Technology, 2009) as a “model for enabling on-demand network
access to a shared pool of configurable computing resources (e.g., networks, servers, storage, applications, and services) that can be rapidly provisioned and released with minimal management effort or service provider interaction.”
Infrastructure as a service (IaaS), Platform as a service (PaaS), and Software as a service (SaaS) are the classical categories of cloud services, although there are other proposed categories such as Database as a Service (DBaaS), Cache as a Service (CaaS), Unified Communications as a Service (UCaaS). In fact, cloud services are becoming so popular that some authors mention the category Everything as a Service (XaaS).
One of the many difficult decisions facing Information Technol- ogy (IT) managers nowadays is to choose between adopting an IT service in its cloud model and having the service hosted according to the conventional, on-premises model. The manager has to consider a large number of criteria, with cost being possibly the most important one. Cloud services are attractive because of the low-initial investment involved. However, if a cloud service is adopted by an organization, its IT department will no longer have any control over the infrastructure, and will completely rely upon the fulfillment of the Service-level Agreement (SLA) clauses in the contract to obtain the required service.
In this paper, we aim to shed some light on the business management problem of identifying the factors and parameters to determine the advantages and disadvantages of using cloud services in comparison with on-premises solutions for enterprise business applications. Furthermore, we focus on modeling and journal homepage:www.elsevier.com/locate/jnca
Journal of Network and Computer Applications
http://dx.doi.org/10.1016/j.jnca.2015.07.002
1084-8045/& 2015 Elsevier Ltd. All rights reserved. n
Corresponding author.
E-mail addresses:[email protected](M. Ribas),
[email protected](C.G. Furtado),[email protected](J.N. de Souza),
gcb@fisica.ufc.br(G.C. Barroso),[email protected](A. Moura),
[email protected](A.S. Lima),fl[email protected](F.R.C. Sousa). 1Rua Francisco Teixeira Alcantara, 500, Fortaleza CEP 60182360, Brazil. 2Rua Juvenal Galeno, 722, Benfica CEP 60015-340, Brazil.
3UFC-DC-Campus do Pici, Bloco 910, 60440-504 Fortaleza, CE, Brazil. 4Rua Princesa Isabel, 1618/101, Fortaleza CEP 60.015-061, CE, Brazil. 5Av. Aprigio Velloso 882 Bloco CN Sala 210 CEP 58429-140 Campina Grande, PB, Brazil.
6Rua Bento Albuquerque, 550 Apto 300, Coco, Fortaleza Cep 60192-060, –Ceara, Brazil.
7Rua Bento Albuquerque, 550 Apto 550, Coco, Fortaleza Cep 60192-060, –Ceara, Brazil.
A case study using distributed caches
Corneli G. F. Júnior*, L. C. Marques VasconcelosϮ, G. C. Barroso♯, J. M. SoaresϮ, L. F. LeiteϮ * Federal Institute of Ceará, Department of Telematics
Email: [email protected]
Ϯ Federal University of Ceará, Department of Teleinformatic
Email: [email protected], [email protected], [email protected]
♯ Federal University of Ceará, Department of Physics
Email: [email protected]
Abstract — A typical problem when executing simulation of
large and complex Coloured Petri Nets (CPN) is the excessive demand for computational resources. In some cases, slowness is the major problem, but in extreme situations, simulation can abort before completion. In addition, to analyze and extract results from large simulation models can be quite complex. An alternative way to deal with these problems is to fragment large CPN models into smaller nets and conceive models as distributed systems (DS). In this work, we present the Distributed Fusion Places (DFP), one new node to compose distributed CPN, which support communication and interaction between geographically dispersed subnets, which together make up a larger, unique and coherent model. In this way, different processes execute subparts of a single model, processing part of the computational effort needed to simulate the global model. Results obtained from distinct parts of the model can be analyzed individually or consolidated to represent the overall system operation. To demonstrate and validate this approach, we have introduced CacheSIM, a simulator conceived to analyze file admission and substitution policies in systems with distributed caches.
Keywords - Distributed Fusion Places, Coloured Petri Nets, Distributed Simulations.
I. INTRODUCTION
Real world systems are normally composed of several parts that present autonomous behaviors and occasionally communicate and cooperate among themselves. To handle the complexity in the design, analysis and development of this type of distributed system (DS), and aiming at minimizing design flaws, modeling and simulation must be used.
Coloured Petri Nets (CPN) can easily model the characteristics of DS, which include concurrence, synchronization, sequence, and conflict among others. There are several commercial tools available for building models and providing simulations of CPN that represent distributed solutions as blocks of a single model, centralized. However, in DS, where the complexity of representation and development is greater than systems with a shared memory, represent DS as a single model can hinder the analysis and reuse of model- specific parts, degrade performance in the simulations, as well as increase the cost of system specification.
An alternative way to deal with this problem is to build simulation models as part of a DS. The idea is to have different processes concurrently simulating different parts of a model.
Each process performs part of the necessary processing of the overall model, and finally, the results can be consolidated to allow a full system analysis or analyzed promptly, for example, inferring the performance of a set of components or parts of a DS in the macro system.
However, because of the interdependence between events