Distributed computing systems
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Distributed Computing Systems CSCI 6900/4900 Review Design goals Resource availability to users Transparency Openness Scalability Security and privacy Hardware concepts Multiprocessors Vs. Multicomputers Bus-based Vs. Switch-based Homogenous Vs. Heterogenous Software Concepts

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Presentation Transcript

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Review

  • Design goals

    • Resource availability to users

    • Transparency

    • Openness

    • Scalability

    • Security and privacy

  • Hardware concepts

    • Multiprocessors Vs. Multicomputers

    • Bus-based Vs. Switch-based

    • Homogenous Vs. Heterogenous


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Software Concepts

  • Functionalities

    • Resource managers

    • Hiding intricacies and heterogeneity

  • Two kinds of operating systems

    • Tightly coupled (distributed operating system)

    • Loosely coupled (network operating system)

  • Middleware

    • Providing transparency for loosely coupled systems



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Uniprocessor Operating Systems

  • Virtualize physical devices (manages devices, protects users)

  • Two modes (User, Kernel)

  • Two kinds (Monolithic, microkernel)

1.11

  • Separating applications from operating system code through

  • a microkernel.


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Multiprocessor Operating Systems

  • Similar in many aspects to uni-processor systems

  • Main extension is how shared memory access is handled

    • Guard against simultaneous access to provide consistency

  • Two primitives

    • Semaphores

      • Two atomic primitives (UP and DOWN)

    • Monitors


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Monitors

monitor Counter {

private:

int count = 0;

public:

int value() { return count;}

void incr () { count = count + 1;}

void decr() { count = count – 1;}

}

  • Borrowed from programming languages

  • Has data and procedures

  • One process can execute at any point of time


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Monitors (2)

monitor Counter {

private:

int count = 0;

int blocked_procs = 0;

condition unblocked;

public:

int value () { return count;}

void incr () {

if (blocked_procs == 0)

count = count + 1;

else

signal (unblocked);

}

void decr() {

if (count ==0) {

blocked_procs = blocked_procs + 1;

wait (unblocked);

blocked_procs = blocked_procs – 1;

}

else

count = count – 1;

}

}

  • Monitors can be used to conditionally block processes

  • Producers/consumers scenario


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Multicomputer Operating Systems

1.14

  • Communication is only through message passing

  • Layer on top of local kernels for coordination and management of remote resources


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Multicomputer Operating Systems (2)

1.15

  • Two buffering places

  • Four blocking points for sender (S1, S2, S3, S4)

  • One blocking point for receiver (S3)


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Communication Reliability & Synchronization

  • Message passing semantics also depends upon reliability of communication


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Distributed Shared Memory Systems (1)

  • Programming harder without the notion of shared address space

  • DSM emulates shared memory using message passing primitives

  • 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


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Effect of Page Size on DSM Performance

1.18

  • Cost of page transfer is dominated by setup costs

  • False sharing results in unnecessary data transfers


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Network Operating System

1-19

  • Collection of heterogeneous systems

  • Facilitates users to access services on specific machines (rlogin, rcp, etc.)


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Network Operating System (2)

1-20

  • Global file systems facilitate convenient data sharing

  • File servers execute requests and send replies


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Global File Systems

1.21

  • Different clients may mount the servers in different places.


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DOS Vs. NOS

  • DOS

    • Transparency

    • Ease of use & security

  • NOS

    • Scalability

    • Openness

  • Can we have best of both worlds?


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Middleware

  • Layer on top of Network OS services

  • Hide heterogeneity

  • Doesn’t manage individual nodes

  • Provides complete set of services


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Middleware Models & Services

  • Models

    • File model

    • Distributed file systems

    • Remote procedure calls

    • Distributed objects

    • Distributed document systems

  • Services

    • Communication facilities

    • Naming

    • Persistence

    • Transactions


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Middleware and Openness

  • Common protocols

  • Common interfaces

  • Completeness


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Comparison between Systems

  • A comparison between multiprocessor operating systems, multicomputer operating systems, network operating systems, and middleware based distributed systems.


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