Chap 01

Definition of a Distributed System (1) ,[object Object],[object Object]

Definition of a Distributed System (2) A distributed system organized as middleware. Note that the middleware layer extends over multiple machines. 1.1

Transparency in a Distributed System Different forms of transparency in a distributed system. Hide whether a (software) resource is in memory or on disk Persistence Hide the failure and recovery of a resource Failure Hide that a resource may be shared by several competitive users Concurrency Hide that a resource may be shared by several competitive users Replication Hide that a resource may be moved to another location while in use Relocation Hide that a resource may move to another location Migration Hide where a resource is located Location Hide differences in data representation and how a resource is accessed Access Description Transparency

Scalability Problems Examples of scalability limitations. Doing routing based on complete information Centralized algorithms A single on-line telephone book Centralized data A single server for all users Centralized services Example Concept

Scaling Techniques (1) 1.4 ,[object Object],[object Object],[object Object]

Scaling Techniques (2) 1.5 An example of dividing the DNS name space into zones.

Hardware Concepts 1.6 Different basic organizations and memories in distributed computer systems

Multiprocessors (1) ,[object Object],1.7

Multiprocessors (2) ,[object Object],[object Object],1.8

Homogeneous Multicomputer Systems ,[object Object],[object Object],1-9

Software Concepts ,[object Object],[object Object],[object Object],[object Object],Provide distribution transparency Additional layer atop of NOS implementing general-purpose services Middleware Offer local services to remote clients Loosely-coupled operating system for heterogeneous multicomputers (LAN and WAN) NOS Hide and manage hardware resources Tightly-coupled operating system for multi-processors and homogeneous multicomputers DOS Main Goal Description System

Uniprocessor Operating Systems ,[object Object],[object Object],1.11

Multiprocessor Operating Systems (1) ,[object Object],monitor Counter { private: int count = 0; public: int value() { return count;} void incr () { count = count + 1;} void decr() { count = count – 1;} }

Multiprocessor Operating Systems (2) ,[object Object],[object Object],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; } }

Multicomputer Operating Systems (1) ,[object Object],1.14

Multicomputer Operating Systems (2) ,[object Object],1.15

Multicomputer Operating Systems (3) ,[object Object],Necessary No Block sender until message delivered Necessary No Block sender until message received Not necessary No Block sender until message sent Not necessary Yes Block sender until buffer not full Reliable comm. guaranteed? Send buffer Synchronization point

Distributed Shared Memory Systems (1) ,[object Object],[object Object],[object Object]

Distributed Shared Memory Systems (2) ,[object Object],1.18

Network Operating System (1) ,[object Object],1-19

Network Operating System (2) ,[object Object],1-20

Network Operating System (3) ,[object Object],1.21

Positioning Middleware ,[object Object],1-22

Middleware and Openness ,[object Object],1.23

Comparison between Systems ,[object Object],Open Open Closed Closed Openness Varies Yes Moderately No Scalability Per node Per node Global, distributed Global, central Resource management Model specific Files Messages Shared memory Basis for communication N N N 1 Number of copies of OS No No Yes Yes Same OS on all nodes High Low High Very High Degree of transparency Multicomp. Multiproc. Middleware-based OS Network OS Distributed OS Item

Clients and Servers ,[object Object],1.25

An Example Client and Server (1) ,[object Object]

An Example Client and Server (2) ,[object Object]

An Example Client and Server (3) ,[object Object],1-27 b

Processing Level ,[object Object],1-28

Multitiered Architectures (1) ,[object Object],1-29

Multitiered Architectures (2) ,[object Object],1-30

Modern Architectures ,[object Object],1-31

Chap 01

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Chap 01