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Distributed computing(1).pptx unit 1 3CSE DEPARTMENTAL ELECTIVE
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- 2. Distributed computing A distributedsystem is a collection of independent computers, interconnected via a network, capable of collaborating on a task. Distributed comput0ing is computing performed in a distributed system.
- 3. The definition ofdistributed systems deals with two aspects that: • Deals with hardware: The machines linked in a distributed system are autonomous. • Deals with software: A distributed system gives an impression to the users that they are dealing with a single system.
- 4. Features of DistributedSystems: • No common physical clock - refers to a system or scenario where different components (e.g., devices, subsystems, or processors) are not synchronized by a single, shared clock signal. In other words, each component or part of the system operates independently, with its own internal clock or timing mechanism. This is an important assumption because it introduces the element of “distribution” in the system and gives rise to the inherent asynchrony amongst the processors.
- 5. • No sharedmemory - refers to a system or architecture in which different components (such as processors, cores, or nodes) do not have access to a common memory space. Each component has its own private memory, and there is no direct, centralized memory that can be accessed by multiple components simultaneously. This concept is relevant in computer architecture, parallel computing, and distributed systems.
- 6. • Autonomy: • Autonomyrefers to the ability of a system or component to operate independently and make decisions without needing to rely on a central authority or other components. In the context of distributed systems, autonomy means that each component (such as a node, agent, or processor) has the ability to function on its own, without constant coordination or supervision from a central system.
- 7. • Heterogeneity: • Heterogeneityrefers to the diversity or difference in the components, technologies, or resources within a system. In computing, this usually refers to the presence of different types of hardware, software, or networks that coexist and interact within the same system. Systems that are heterogeneous consist of a variety of different entities that might have different architectures, operating systems, hardware platforms, or protocols.
- 8. Issues in distributedsystems Heterogeneity • Openness • Security • Scalability • Failure handling • Concurrency • Transparency • Quality of service
- 9. QOS parameters (Qualityof Service) • The distributed systems must offer the following QOS: • ➢ Performance • ➢ Reliability • ➢ Availability • ➢ Security
- 10. Differences between centralizedand distributed systems • Centralized Systems • In Centralized Systems, several jobs are done on a particular central processing unit(CPU) • They have shared memory and shared variables. • Clocking is present.
- 11. Distributed Systems • InDistributed Systems, jobs are distributed among several processors. The Processor are interconnected by a computer network • They have no global state (i.e.) no shared memory and no shared variables. • No global clock.
- 12. 1.2 Relation toComputer System Components
- 13. • As shownin Fig 1.1, Each computer has a memory-processing unit and the computers are connected by a communication network. Each system connected to the distributed networks hosts distributed software which is a middleware technology. This drives the Distributed System (DS) at the same time preserves the heterogeneity of the DS. The term computation or run in a distributed system is the execution of processes to achieve a common goal.
- 14. 1.3 Motivation • •Inherently distributed computations: DS can process the computations at geographically remote locations. • • Resource sharing: The hardware, databases, special libraries can be shared between systems without owning a dedicated copy or a replica. This is cost effective and reliable. • Access to geographically remote data and resources: As mentioned previously, computations may happen at remote locations. Resources such as centralized servers can also be accessed from distant locations.
- 15. • •• Enhancedreliability: DS provides enhanced reliability, since they run on multiple copies of resources. The distribution of resources at distant locations makes them less susceptible for faults. The term reliability comprises of: • 1. Availability:the resource/ service provided by the resource should be accessible at all times • 2. Integrity: the value/state of the resource should be correct and consistent. • 3. Fault-Tolerance:the ability to recover from system failures
- 16. • • Increasedperformance/cost ratio: The resource sharing and remote access features of DS naturally increase the performance / cost ratio. • • Scalable: The number of systems operating in a distributed environment can be increased as the demand increases.
- 17. 1.5 MESSAGE-PASSING SYSTEMSVERSUS SHARED MEMORY SYSTEMS • Message passing systems: • • This allows multiple processes to read and write data to the message queue without being connected to each other. • Messages are stored on the queue until their recipient retrieves them. Message queues are quite useful for interprocess communication and are used by most operating systems.
- 18. Shared memory systems: •The shared memory is the memory that can be simultaneously accessed by multiple processes. This is done so that the processes can communicate with each other. • Communication among processors takes place through shared data variables, and control variables for synchronization among the processors. • Semaphores and monitors are common synchronization mechanisms on shared memory systems. • When shared memory model is implemented in a distributed environment, it is termed as distributed shared memory.
- 19. a) Message PassingModel b) Shared Memory Model
- 22. 1.6 PRIMITIVES FORDISTRIBUTED COMMUNICATION • 1.6.1 Blocking / Non blocking / Synchronous / Asynchronous
- 28. Processor Synchrony • Processorsynchrony indicates that all the processors execute in lock- step with their clocks synchronized.
- 29. SYNCHRONOUS VS ASYNCHRONOUS EXECUTIONS •The execution of process in distributed systems may be synchronous or asynchronous. • Asynchronous Execution: A communication among processes is considered asynchronous, when every communicating process can have a different observation of the order of the messages being exchanged. • In an asynchronous execution: there is no processor synchrony and there is no bound on the drift rate of processor clocks • • message delays are finite but unbounded • • no upper bound on the time taken by a process
- 30. Synchronous Execution: • Acommunication among processes is considered synchronous when every process observes the same order of messages within the system. • In the same manner,the execution is considered synchronous, when every individual process in the system observes the same total order of all the processes which happen within it. • In an synchronous execution: • • processors are synchronized and the clock drift rate between any two processors is • bounded • • message delivery times are such that theyoccur in one logical step or round • • upper boundon the time taken by a process to execute a step.
- 31. DESIGN ISSUES ANDCHALLENGES IN DISTRIBUTED SYSTEMS • The design of distributed systems has numerous challenges. • They can be categorized into: • • Issues related to system and operating systems design • • Issues related to algorithm design • • Issues arising due to emerging technologies • The above three classes are not mutually exclusive
- 32. Issues related tosystem and operating systems design