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Distributed Systems CS 654 Lecture 3 September 11 th , 2006 Basic Categories Uniprocessor Operating Systems 1.11 Microkernel design What does a monolithic design look like? What does a SMP OS look like? Multicomputer Operating Systems 1.14 Is the middle layer in kernel mode?

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distributed systems

Distributed Systems

CS 654Lecture 3September 11th, 2006

uniprocessor operating systems
Uniprocessor Operating Systems

1.11

  • Microkernel design
  • What does a monolithic design look like?
  • What does a SMP OS look like?
multicomputer operating systems
Multicomputer Operating Systems

1.14

  • Is the middle layer in kernel mode?
communications
Communications
  • Fundamentally, how is communication done on SMP vs. a cluster (multicomputer)?
  • From the programming point of view, what are the two fundamental ways to communicate?
  • Is it possible to communicate using the network within an SMP?
  • Is it possible to provide a shared memory model on cluster?
slide6
DSM
  • What is virtual memory?
  • Where are the page frames stored when paged (swapped) out?
distributed shared memory systems 1
Distributed Shared Memory Systems (1)
  • Pages of address space distributed among four machines
  • Situation after CPU 1 references page 10
  • Situation if page 10 is read only and replication is used
  • What kinds of bad things can happen?
    • Using to communicate would be bad.
distributed shared memory systems 2
Distributed Shared Memory Systems (2)

1.18

  • False sharing of a page between two independent processes.
examples of dos
Examples of DOS?
  • DSM can be considered a failure.
    • MPI is the norm.
network operating system 1
Network Operating System (1)
  • General structure of a network operating system.
    • Generally, services are not in the kernel.
  • Services are remote login, file access, etc.
network operating system 2
Network Operating System (2)

1-20

  • Two clients and a server in a network operating system.
network operating system 3
Network Operating System (3)

1.21

  • Different clients may mount the servers in different places.
  • Examples of NOS?
middleware
Middleware
  • What is middleware?
  • What is its function?
  • Where is it located?
  • Why does it exist?
positioning middleware
Positioning Middleware
  • General structure of a distributed system as middleware.
figure 2 1 software and hardware service layers in distributed systems
Figure 2.1Software and hardware service layers in distributed systems

Instructor’s Guide for Coulouris, Dollimore and Kindberg Distributed Systems: Concepts and Design Edn. 4 © Pearson Education 2005

middleware and openness
Middleware and Openness
  • In an open middleware-based distributed system, the protocols used by each middleware layer should be the same, as well as the interfaces they offer to applications.
  • Why should they be open? Why should they not be open?

1.23

typical middleware services
Typical Middleware Services
  • Communication
  • Naming
  • Persistence
  • Distributed transactions
  • Security
middleware models
Middleware Models
  • Distributed files
    • Examples?
  • Remote procedure call
    • Examples?
  • Distributed objects
    • Examples?
  • Distributed documents
    • Examples?
  • Others?
    • Message-oriented middleware (MOM)
    • Service oriented architecture (SOA)
    • Document-oriented
dos vs nos vs middleware discussion
DOS vs. NOS vs. Middleware Discussion
  • What is good/bad about DOS?
    • Transparency
    • Other issues have reduced success.
    • Problems are often socio-technological.
  • What is good/bad about NOS?
    • Simple.
    • Decoupled, easy to add/remove.
    • Lack of transparency.
  • What is good/bad about middleware?
    • Easy to make multiplatform.
    • Easy to start something new.
      • But this can also be bad.
example
Example
  • A user wants to access a file on a cluster. How should we design this?
  • Issues?
    • Transparency
    • Fault tolerance
  • Possibilities:
    • SAN
      • Shared?
      • GFS
    • NFS
    • Middleware?
  • What should we do differently if it is on a WAN?
example22
Example
  • A process is started on a cluster via the fork system call. How should we design this?
  • Issues
    • Load balancing
    • Transparency, networking
  • Possibilities
    • Do nothing.
    • User picks machine, uses ssh.
    • System call.
      • Disadvantages?
    • Library function.
      • Transparency?
discussion
Discussion
  • Have NOS been successful?
  • Have DOS been successful? Why or why not?
    • An abstraction that is too leaky?
  • Has middleware been successful?
leaky abstractions
“Leaky” Abstractions
  • What is an abstraction?
  • What is encapsulation?
  • How well does this work in practice?
    • High-level languages
    • TCP/IP, reliable byte sequence
      • Packet size?
      • Ignore packet loss?
      • Reliability?
figure 1 1 a typical portion of the internet

intranet

%

%

ISP

%

%

backbone

satellite link

desktop computer:

server:

network link:

Figure 1.1A typical portion of the Internet

Instructor’s Guide for Coulouris, Dollimore and Kindberg Distributed Systems: Concepts and Design Edn. 4 © Pearson Education 2005

figure 1 2 a typical intranet
Figure 1.2A typical intranet

Instructor’s Guide for Coulouris, Dollimore and Kindberg Distributed Systems: Concepts and Design Edn. 4 © Pearson Education 2005

figure 1 3 portable and handheld devices in a distributed system
Figure 1.3Portable and handheld devices in a distributed system

Instructor’s Guide for Coulouris, Dollimore and Kindberg Distributed Systems: Concepts and Design Edn. 4 © Pearson Education 2005

what are typical latencies and bandwidths
What are typical latencies and bandwidths?
  • WAN?
    • Millisecs
    • Anywhere from Mbps to Gbps
  • LAN?
    • Microsecs
    • Anywhere from Mbps to Gbps
  • Mobile?
    • Microsecs to days
    • Anywhere from Mbps to Kbps
figure 1 4 web servers and web browsers

http://www.google.comlsearch?q=kindberg

www.google.com

Browsers

Web servers

Internet

www.cdk3.net

http://www.cdk3.net/

www.w3c.org

http://www.w3c.org/Protocols/Activity.html

File system of

Protocols

www.w3c.org

Activity.html

Figure 1.4Web servers and web browsers

Instructor’s Guide for Coulouris, Dollimore and Kindberg Distributed Systems: Concepts and Design Edn. 4 © Pearson Education 2005

figure 1 5 computers in the internet

Computers

Date

Web servers

188

0

1979, Dec.

1989, July

130,000

0

1999, July

56,218,000

5,560,866

2003, Jan.

171,638,297

35,424,956

Figure 1.5Computers in the Internet

Instructor’s Guide for Coulouris, Dollimore and Kindberg Distributed Systems: Concepts and Design Edn. 4 © Pearson Education 2005

figure 1 6 computers vs web servers in the internet
Figure 1.6Computers vs. Web servers in the Internet

Date

Computers

Web servers

Percentage

1,776,000

130

0.008

1993, July

1995, July

6,642,000

23,500

0.4

1997, July

19,540,000

1,203,096

6

1999, July

56,218,000

6,598,697

12

2001, July

125,888,197

31,299,592

25

42,298,371

Instructor’s Guide for Coulouris, Dollimore and Kindberg Distributed Systems: Concepts and Design Edn. 4 © Pearson Education 2005

why did the web succeed
Why Did the Web Succeed?
  • Timing
    • Need a critical mass of
      • Internet
      • Users with PCs
  • Technology
    • Provided enough functionality, without providing too much
      • What would have been the wrong design?
  • How good is HTTP?
    • Connections are expensive to set-up/tear-down.
    • No pipelining
    • No chunking
client server
Client-Server
  • What is a client?
  • What is a server?
  • What would be the alternative?
  • Can something be both client and server?
figure 2 2 clients invoke individual servers
Figure 2.2Clients invoke individual servers

Instructor’s Guide for Coulouris, Dollimore and Kindberg Distributed Systems: Concepts and Design Edn. 4 © Pearson Education 2005

clients and servers
Clients and Servers
  • General interaction between a client and a server.
an example client and server 1
An Example Client and Server (1)
  • The header.h file used by the client and server.
an example client and server 3
An Example Client and Server (3)

1-27 b

  • A client using the server to copy a file.
layering
Layering
  • Why layer?
    • Flexible
      • You can add functionality without changing underlaying layers.
    • Reuse
      • Many applications can use Java jars, for example.
    • Helps you solve the problem.
      • Too hard to hold everything in your head at once.
buying an airline ticket
Buying an airline ticket
  • How would you design the system?
    • A terminal on one end, write a single program on the other end.
    • A single program at the agent end. All things are broadcast to everyone.
3 tier architectures
3-Tier Architectures
  • Interface
  • (Business) logic
  • Database
processing level
Processing Level
  • The general organization of an Internet search engine into three different layers

1-28

multitiered architectures 2
Multitiered Architectures (2)
  • An example of a server acting as a client.

1-30

peer to peer
Peer-to-Peer
  • How does it differ from previous?
  • Can all apps be done as P2P?
figure 2 3 a distributed application based on peer processes
Figure 2.3A distributed application based on peer processes

Instructor’s Guide for Coulouris, Dollimore and Kindberg Distributed Systems: Concepts and Design Edn. 4 © Pearson Education 2005

modern architectures
Modern Architectures
  • An example of horizontal distribution of a Web service.

1-31

figure 2 4 a service provided by multiple servers
Figure 2.4A service provided by multiple servers

Instructor’s Guide for Coulouris, Dollimore and Kindberg Distributed Systems: Concepts and Design Edn. 4 © Pearson Education 2005

figure 2 5 web proxy server
Figure 2.5Web proxy server

Instructor’s Guide for Coulouris, Dollimore and Kindberg Distributed Systems: Concepts and Design Edn. 4 © Pearson Education 2005

figure 2 6 web applets
Figure 2.6Web applets

Instructor’s Guide for Coulouris, Dollimore and Kindberg Distributed Systems: Concepts and Design Edn. 4 © Pearson Education 2005

figure 2 7 thin clients and compute servers
Figure 2.7Thin clients and compute servers

Compute server

Network computer or PC

Application

network

Thin

Process

Client

Instructor’s Guide for Coulouris, Dollimore and Kindberg Distributed Systems: Concepts and Design Edn. 4 © Pearson Education 2005