분산 시스템 시험 문제

흠냐.. 교수님이 뽑아 주신 문제 들입니다. 문제 근처에 있는 번호는 관련된 PPT 페이지 번호죠. 저는 지금 부터 저 PPT에 있는 내용을 외워야 합니다. 공부하기 전에 써봅니다.

공부 좀 해야겠네요.

정리 끝~ 워드로 4장 반 분량이네요. 요걸 외우면 시험 잘 본다는거..
[#M_ more.. | less.. |

분산시스템 정의: A collection of independent computers that appears to its users as a
single coherent system.

 

미들웨어의 위치와 정의:  Middleware : organized by means of a layer of software that is
logically placed between a higher-level layer consisting of users and
applications

 

분산 시스템의 예: 학교 시스템, 주문
처리 정보 시스템, WWW

 

분산 시스템 목적: Connecting Users and Resources, Transparency,
Openness, Scalability

 

투명성이 무엇이냐: To hide the fact that its
processes and resources are physically distributed across multiple computers

 

투명성 예:

 

개방성이 무엇이고 무엇을 하기 위해 필요한 것이 무엇인가?

다른 시스템에서 제공하는 서비스를 서로 사용할 수 있도록 하는 것. Portability,
Flexibility, Extensibility 를 고려해야 한다.

 

확장성 이란? 시스템을 확장할 때 비용이 적게 들고 퍼포먼스가 좋아질수록
확장성이 좋다.

 

 

 

Three techniques for scaling

n  Hiding communication latencies

n 
Asynchronous communication

n 
More or less independent tasks
can be scheduled for execution while another task is waiting for communication
to complete.

n  Distribution : Decomposition

n 
Taking a component, splitting
it into smaller parts and subsequently spreading those parts across the system.

n  Replication of Components

n 
Replicate components across a
distributed system

하드웨어 구조

멀티 프로세서, 멀티 컴퓨터

 

멀티 프로세서의 문제: coherent memory -> 버스가
과다 사용(overload)되기 때문에 성능이 저하 된다 -> 버스와
메모리 사이에 캐시를 사용한다(자주 사용하는 정보를 가지고 있는다.).

그러나.. Cache coherent problem 발생 = 제한된 Scalability로 인해 병목 현상 발생한다. -> 메모리를 모듈별로 쪼개서 크로스바 스위치 사용 -> 그러나
크로스바 스위치의 문제 발생 = 크로스바 스위치 비용이 크다.
=> 오메가 스위치 사용 => 스위치 비용 줄여야 한다 => Hierarchical systems = 몇몇 메모리를 CPU에
담당 시킨 것. => Homogeneous Multicomputer Systems(Bus-based
multicomputer => Switch-based multicomputer)

 

 

Network Operating System

n  Advantage

n  Scalability

n  Openness

n  Disadvantage

n  Transparency

n  Usability

 

Middleware

n  Consider the definition of distributed system

n  Independent computers => NOS

n 
Scalability and Openness

n  Single System Image => DOS

n 
Transparency and Usability

n  Middleware

n  An additional layer of software between applications and NOS

n 
is used in NOS to more or less
hide the heterogeneity of the collection of underlying platforms

n 
also to improve distribution
transparency and advanced communication facilities and to provide various
services

 

Middleware Model

n  Distributed File System

n  All resources are treated as files

n  No difference between local and remote files

n  Remote Procedure Call    

n  Emphasis on hiding network communication by allowing a process to
call a procedure of which an implementation is located on a remote machine

n  Distributed Object

n  Each object implements an interface that hides all the internal
details of the object from its users

n  The Web Model

n  Extremely simplifies the use of network resources (distributed
documents model)

 

Middleware Model

n  Distributed File System

n  All resources are treated as files

n  No difference between local and remote files

n  Remote Procedure Call    

n  Emphasis on hiding network communication by allowing a process to
call a procedure of which an implementation is located on a remote machine

n  Distributed Object

n  Each object implements an interface that hides all the internal
details of the object from its users

n  The Web Model

n  Extremely simplifies the use of network resources (distributed
documents model)

 

Middleware Services

n  Access Transparency

n  RPC, remote invocation, distributed file systems, distribute
database

n  Naming

n  Name services allow entities to be shared and looked up (as in
directories)

n  URL

n  Persistency

n  Distributed Transaction

n 
Allows multiple read and write
operations to occur atomically

n  Atomicity

n  Security

n  Combined with the need for extensibility, security has turned out to
be one of the hardest services to implement in DSs

 

Application Layering

n  User-Interface Level

n  Processing Level

n  Data Level

 

2-Tier vs. 3-Tier Client/Server

n  2-tier client/server system

n  the application logic is either inside the user interface on the
client or within the Database on the server (or both)

n  Ex) file server, database server with stored procedures

n  3-tier client/server system

n  the application logic lives in the middle-tier

n  In theory, 3-tier systems are more scalable, robust, and flexible.

n  The can integrate data from multiple sources on heterogeneous
systems

n  Ex) TP Monitors, Distributed Objects, and the Web

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